BACKGROUND

Refrigeration systems absorb thermal energy from heat sources operating at temperatures below the temperature of the surrounding environment and discharge thermal energy into the surrounding environment. Heat sources operating at temperatures above the surrounding environment can be naturally cooled by the surrounding if there is direct contact between the source and the environment.

Conventional refrigeration systems include a compressor, a heat rejection exchanger (i.e., a condenser), a receiver, an expansion device, and a heat absorption exchanger (i.e., an evaporator). Such systems can be used to maintain operating temperature set points for a wide variety of cooled heat sources (loads, processes, equipment, systems) thermally interacting with the evaporator. Closed-circuit refrigeration systems may pump significant amounts of absorbed thermal energy from heat sources into the surrounding environment.

In closed-circuit systems, compressors are used to compress vapor from an evaporating pressure the evaporator and to a condensing pressure in the condensers and condense the compressed vapor converting the vapor into a liquid at a temperature higher than the surrounding environment temperature. The combination of condensers and compressors can add a significant amount of weight and can consume relatively large amounts of electrical power. In general, the larger amount of absorbed thermal energy that the system is designed to handle, the heavier the refrigeration system and the larger amount of power consumed during operation, even when cooling of a heat source occurs over relatively short time periods.

In some cases the surrounding environment temperature can appear below the heat source temperature. The refrigeration system provides a contact via refrigerant. There may be no need to compress vapor from the evaporating to condensing pressure since condensation can happen at a pressure slightly higher or even below the evaporating pressure. SUMMARY

This disclosure describes techniques related to systems and methods for thermal management. In an example implementation, a heat transfer apparatus includes a plurality of “n” number of control valves, each of the plurality of “n” number of control valves including a control valve inlet and a control valve outlet; a like plurality of “n” number of evaporator sections, each of the like plurality of “n” number of evaporator sections including an evaporator section inlet and an evaporator section outlet, each evaporator section inlet fluidly coupled to a corresponding one of the plurality of “n” number of control valve outlets, each evaporator section configured to extract heat from at least one heat load that is in thermal conductive or convective contact or proximate to the evaporator section; a refrigerant fluid inlet fluidly coupled to the like plurality of evaporator sections; and a refrigerant fluid outlet fluidly coupled to the like plurality of evaporator sections.

In an aspect combinable with the example implementation, the plurality of “n” number of control valves are fluidly coupled between the refrigerant fluid inlet and the evaporator outlets.

In another aspect combinable with any of the previous aspects, each of the plurality of “n” number of control valves is configured to receive a control signal.

In another aspect combinable with any of the previous aspects, the refrigerant fluid inlet includes an inlet distributor having a plurality of outlets, with each of the plurality of outlets being coupled to the inlet of a corresponding one of the plurality of “n” number of control valves.

In another aspect combinable with any of the previous aspects, the refrigerant fluid outlet includes an outlet collector having a plurality of inlets, with each of the plurality of inlets being coupled to the evaporator section outlet of a corresponding one of the like plurality of evaporator sections.

In another aspect combinable with any of the previous aspects, the plurality of “n” number of control valves are configured to selectively expand a refrigerant fluid to generate a refrigerant fluid mixture including liquid refrigerant fluid and refrigerant fluid vapor; and direct the refrigerant fluid mixture into the corresponding like plurality of evaporator sections.

In another aspect combinable with any of the previous aspects, the plurality of “n” number of control valves include expansion valves that are further configured to selectively stop a refrigerant fluid flow through the expansion valves.

In another example implementation, a method of cooling at least one heat load includes providing a flow of a refrigerant fluid to a refrigerant fluid inlet of a heat transfer device; providing the flow of the refrigerant fluid from the refrigerant fluid inlet to a plurality of “n” number of control valves, each of the plurality of “n” number of control valves including a control valve inlet and a control valve outlet; providing the flow of the refrigerant fluid from the refrigerant fluid inlet to a like plurality of “n” number of evaporator sections, each of the like plurality of “n” number of evaporator sections including an evaporator section inlet and an evaporator section outlet, each evaporator section inlet fluidly coupled to a corresponding one of the plurality of “n” number of control valve outlets; extracting heat, with at least one evaporator section, from at least one heat load that is in thermal conductive or convective contact or proximate to the evaporator section; and providing the flow of the refrigerant fluid through a refrigerant fluid outlet fluidly coupled to the like plurality of evaporator sections.

An aspect combinable with the example implementation further includes expanding, in at least one of the a plurality of “n” number of control valves, the refrigerant fluid to generate a refrigerant fluid mixture including liquid refrigerant fluid and refrigerant fluid vapor; and directing the refrigerant fluid mixture into the corresponding at least one evaporator section.

Another aspect combinable with any of the previous aspects further includes selectively stopping the flow of the refrigerant fluid through the heat transfer device with the control valves.

Another aspect combinable with any of the previous aspects further includes directing the refrigerant fluid to enter a first set of “n”-”x” number of the plurality of evaporator sections over a first interval, while inhibiting the refrigerant fluid to enter a second, different set of “x” number of the plurality of evaporator sections over the first interval, where “n” is a total number of the plurality of evaporator sections.

Another aspect combinable with any of the previous aspects further includes switching the refrigerant fluid to direct the transported refrigerant fluid that enters the gated evaporator to contact a third, different set of “n”-”x”’ number of the plurality of evaporator sections over a second, subsequent interval, while inhibiting the refrigerant fluid to enter a fourth, different set of “x”’ number of the plurality of evaporator sections over the second interval.

In another example implementation, a thermal management system includes an open-circuit refrigeration system (OCRS), an exhaust line, and a flow control device. The OCRS includes a receiver configured to store a refrigerant fluid and at least one gated evaporator. The gated evaporator is configured to extract heat from a plurality of heat loads when the plurality of heat loads are in thermal conductive or convective contact or proximate to the gated evaporator. The gated evaporator includes a plurality of “n” number of control valves. Each of the plurality of “n” number of control valves includes a control valve inlet and a control valve outlet. The gated evaporator further includes a like plurality of evaporator sections. Each of the like plurality of evaporator sections includes an evaporator section inlet and an evaporator section outlet. Each evaporator section inlet is coupled to a corresponding one of the plurality of “n” number of control valve outlets. The flow control device includes an inlet and an outlet, with the outlet coupled to an exhaust line. The flow control device is configured to control a refrigerant fluid pressure upstream of the flow control device. The receiver, the gated evaporator, the flow control device, and the exhaust line are fluidly coupled to form an open-circuit refrigerant fluid flow path.

An aspect combinable with the example implementation further includes an inlet distributor coupled to the outlet of the receiver, and having a plurality of outlets, with each of the plurality of outlets being coupled to the inlet of a corresponding one of the plurality of “n” number of control valves.

Another aspect combinable with any of the previous aspects further includes an outlet collector having a plurality of inlets with each of the plurality of inlets being coupled to the evaporator section outlet of a corresponding one of the like plurality of evaporator sections, and having an outlet coupled to the inlet of the flow control device.

In another aspect combinable with any of the previous aspects, the plurality of “n” number of control valves are configured to selectively expand the refrigerant fluid to generate a refrigerant fluid mixture including liquid refrigerant fluid and refrigerant fluid vapor; and direct the refrigerant fluid mixture into the corresponding like plurality of evaporator sections.

In another aspect combinable with any of the previous aspects, the plurality of “n” number of control valves are expansion valves that are further configured to selectively stop refrigerant fluid flow through the expansion valves.

In another aspect combinable with any of the previous aspects, the plurality of “n” number of control valves are expansion valves that are not configured to stop refrigerant fluid flow through the expansion valves, with the system further including a plurality of solenoid control valves coupled to the expansion valves, the plurality of solenoid valves configured to selectively stop the refrigerant fluid flow through the expansion valves.

In another aspect combinable with any of the previous aspects, the plurality of “n” number of control valves are configured to selectively perform a constant- enthalpy expansion of a liquid refrigerant fluid to generate a refrigerant fluid mixture for the like plurality of evaporator sections.

In another aspect combinable with any of the previous aspects, the refrigerant fluid includes ammonia.

In another aspect combinable with any of the previous aspects, the plurality of “n” number of control valves are further configured to control temperatures of the plurality of heat loads.

In another aspect combinable with any of the previous aspects, the flow control device includes a back-pressure regulator connected downstream from the evaporator along the open-circuit refrigerant fluid flow path. In another aspect combinable with any of the previous aspects, the backpressure regulator is configurable to receive refrigerant fluid vapor generated in the gated evaporator and to regulate the pressure of the refrigerant fluid upstream from the back-pressure regulator along the refrigerant fluid flow path.

In another aspect combinable with any of the previous aspects, the backpressure regulator is configurable to discharge the refrigerant vapor through the exhaust line, without returning the refrigerant vapor to the receiver.

In another aspect combinable with any of the previous aspects, the refrigerant fluid from the exhaust line is discharged so that the discharged refrigerant fluid is not returned to the receiver.

Another aspect combinable with any of the previous aspects further includes a control system configured to respond to signals from at least one sensor to control operation of the plurality of “n” number of control valves.

In another aspect combinable with any of the previous aspects, the control system is configured to process the signals from the at least one sensor to switch “x” number of the plurality of “n” number of control valves to inhibit refrigerant flow through the “x” number of the plurality of “n” number of control valves during a period, with “x” having a value that is at least one less than “n”.”

In another aspect combinable with any of the previous aspects, the control system is configured to process signals that are time period signals to indicate that “x” number of uncooled evaporator sections have reached a maximum time period for a heat load operation, with “x” having a value that is at least one less than “n.”

In another aspect combinable with any of the previous aspects, the control system is configured to process signals that are temperature signals to indicate that “x” number of the uncooled evaporator sections have reached the maximum heat load temperature rise during a heat load operation, with “x” having a value that is at least one less than “n.”

In another aspect combinable with any of the previous aspects, the control system is configured to process signals that are temperature signals to indicate that “x” number of uncooled evaporator sections have reached a maximum evaporator section temperature rise during a heat load operation, with “x” having a value that is at least one less than “n.”

In another aspect combinable with any of the previous aspects, the flow control device is a first flow control device, and the system further includes a second flow control device coupled between the receiver outlet and the inlet to the flow distributer, with the second flow control device configured to control vapor quality at the outlet of the gated evaporator.

Another aspect combinable with any of the previous aspects further includes a closed-circuit refrigeration system (CCRS) integrated with the OCRS.

Another aspect combinable with any of the previous aspects further includes a liquid separator having an inlet, a vapor-side outlet, and a liquid-side outlet.

In another aspect combinable with any of the previous aspects, the CCRS includes a compressor having a compressor inlet fluidly coupled to the vapor-side outlet and having a compressor outlet; and a condenser having a condenser inlet fluidly coupled to the compressor outlet and having a condenser outlet coupled to an inlet of the receiver to condense a superheated refrigerant vapor at the condenser inlet by removing heat from the refrigerant fluid.

Another aspect combinable with any of the previous aspects further includes a junction having an inlet fluidly coupled to the vapor-side outlet of the liquid separator and first and second outlets fluidly coupled to the compressor inlet and the inlet of the flow control device.

Another aspect combinable with any of the previous aspects further includes an electronically controllable expansion valve; a sensor disposed downstream of the gated evaporator to generate a sensor signal that directly or indirectly controls the electronically controllable expansion valve.

Another aspect combinable with any of the previous aspects further includes a recuperative heat exchanger that has a first fluid path that receives the refrigerant fluid from the receiver and a second fluid path that receives refrigerant vapor from the vapor-side outlet, with the second fluid path providing thermal contact between the refrigerant fluid leaving the receiver and the refrigerant vapor passing through the recuperative heat exchanger.

In another aspect combinable with any of the previous aspects, the recuperative heat exchanger evaporates any remaining liquid prior to being fed to the inlet of the compressor.

Another aspect combinable with any of the previous aspects further includes an electronically controllable expansion valve; a sensor disposed downstream of the gated evaporator to generate a sensor signal that directly or indirectly controls the electronically controllable expansion valve, with the electronically controlled expansion valve operated with the sensor to maintain a superheat at an outlet of the recuperative heat exchanger.

In another aspect combinable with any of the previous aspects, the recuperative heat exchanger is configured to transfer heat energy from the refrigerant fluid emerging from liquid separator to refrigerant fluid upstream from the electronically controllable expansion valve.

Another aspect combinable with any of the previous aspects further includes an ejector having a primary inlet, a secondary inlet, and an outlet, with the primary inlet fluidly coupled to receive refrigerant from the receiver, and the secondary inlet fluidly coupled to receive refrigerant fluid from the liquid-side outlet of the liquid separator.

In another aspect combinable with any of the previous aspects, the ejector is configured to pump a secondary refrigerant fluid flow received at the secondary inlet from the liquid side outlet using energy of a primary refrigerant flow from the receiver outlet.

Another aspect combinable with any of the previous aspects further includes a pump having an inlet and an outlet, with the inlet fluidly coupled to the liquid-side outlet of the liquid separator and the outlet fluidly coupled to an inlet of the gated evaporator. In another aspect combinable with any of the previous aspects, the pump is configured to circulate a refrigerant fluid flow received from the liquid-side outlet of the liquid separator to the inlet of the gated evaporator.

Another aspect combinable with any of the previous aspects further includes a control system configured to control operation of the gated evaporator, the control system including a processor device, memory and storage operatively connected.

In another aspect combinable with any of the previous aspects, the control system is configured to produce a first control signal to direct transported refrigerant fluid to enter a first set of fewer than the like plurality of evaporator sections over a first interval, and inhibits the refrigerant fluid to enter a second, different set of the fewer than the like plurality of evaporator sections over the first interval; and produce a second control signal to direct the transported refrigerant fluid that enters the gated evaporator to contact a third, different set of the evaporator sections over a second, subsequent interval, and inhibits the refrigerant fluid to enter a fourth, different set of the fewer than the plural evaporator sections over the second interval.

In another example implementation, a thermal management method includes transporting a refrigerant fluid from a receiver, through a gated evaporator having a plurality of evaporator sections configured to extract heat from a plurality of heat loads when the plurality of heat loads are in thermal conductive or convective contact or are in proximity to the gated evaporator, through a flow control device to control to control refrigerant fluid pressure upstream of the flow control device, and to an exhaust line of an open-circuit refrigeration system. The method further includes directing the transported refrigerant fluid to enter a first set of “n”-”x” number of the plurality of evaporator sections over a first interval, while inhibiting the refrigerant fluid to enter a second, different set of “x” number of the plurality of evaporator sections over the first interval, where “n” is a total number of the plurality of evaporator sections. The method further includes switching the refrigerant fluid to direct the transported refrigerant fluid that enters the gated evaporator to contact a third, different set of “n”-”x”’ number of the plurality of evaporator sections over a second, subsequent interval, while inhibiting the refrigerant fluid to enter a fourth, different set of “x”’ number of the plurality of evaporator sections over the second interval. The method further includes discharging refrigerant vapor that is generated by the plurality of heat loads from the exhaust line so that the discharged refrigerant vapor is not returned to the receiver.

In an aspect combinable with the example implementation, the flow control device is a first flow control device, and the method further includes controlling a vapor quality of the refrigerant fluid at an outlet of the gated evaporator by operation of a second flow control device.

In another aspect combinable with any of the previous aspects, switching occurs by controlling operation of a plurality of control valves coupled to a plurality of outlets of an inlet distributor of the gated evaporator, with the plurality of outlets being coupled to inlets of the plurality of evaporator sections.

Another aspect combinable with any of the previous aspects further includes collecting refrigerant flows by an outlet collector having a plurality of inlets coupled to evaporator section outlets.

Another aspect combinable with any of the previous aspects further includes expanding, by the plurality of control valves, the refrigerant fluid to generate a refrigerant fluid mixture including liquid refrigerant and refrigerant vapor; and directing the refrigerant fluid mixture into the corresponding evaporator sections.

In another aspect combinable with any of the previous aspects, the plurality of control valves are expansion valves that are configured to selectively stop refrigerant fluid through the expansion valves.

In another aspect combinable with any of the previous aspects, the plurality of “n” number of control valves are expansion valves that are not configured to stop refrigerant fluid through the expansion valves, and the method further includes operating a plurality of solenoid control valves fluidly coupled to the expansion valves to selectively stop the refrigerant fluid through the expansion valves.

In another aspect combinable with any of the previous aspects, the plurality of control valves are configured to selectively perform a constant-enthalpy expansion of the liquid refrigerant fluid to generate the refrigerant fluid mixture for the evaporator sections.

In another aspect combinable with any of the previous aspects, the refrigerant fluid includes ammonia.

In another aspect combinable with any of the previous aspects, the plurality of control valves are configured to control temperatures of the heat loads.

In another aspect combinable with any of the previous aspects, discharging includes discharging the refrigerant vapor through a back-pressure regulator.

In another aspect combinable with any of the previous aspects, the backpressure regulator is configured to receive refrigerant vapor generated in the gated evaporator and to regulate the pressure of the refrigerant fluid upstream from the back-pressure regulator.

In another aspect combinable with any of the previous aspects, the backpressure regulator is configured to discharge the refrigerant vapor through the exhaust line without returning the refrigerant vapor to the receiver.

In another aspect combinable with any of the previous aspects, the refrigerant fluid from the exhaust line is discharged so that the discharged refrigerant vapor is not returned to the receiver.

Another aspect combinable with any of the previous aspects further includes operating a control system to respond to signals from sensors to control operation of the plurality of control valves; and process the signals from the sensor to switch “x” number of the plurality of control valves to inhibit refrigerant flow through the “x” number of the plurality of control valves during the first interval, with “x” having a value that is at least one less than “n.”

Another aspect combinable with any of the previous aspects further includes operating the control system to process the signals as time period signals to indicate that “x” number of uncooled evaporator sections have reached a maximum time period for proper heat load operation, with “x” having a value that is at least one less than “n”. Another aspect combinable with any of the previous aspects further includes operating the control system to process the signals as temperature signals to indicate that “x” number of the uncooled evaporator sections have reached the maximum heat load temperature rise during the heat load operation, with “x” having a value that is at least one less than “n.”

Another aspect combinable with any of the previous aspects further includes operating the control system to process the signals as temperature signals to indicate that “x” number of uncooled evaporator sections have reached a maximum evaporator section temperature rise during the heat load operation, with “x” having a value that is at least one less than “n.”

In another aspect combinable with any of the previous aspects, the flow control device is a first flow control device, and the method further includes controlling vapor quality at the outlet of the gated evaporator with a second flow control device fluidly coupled between the receiver outlet and the inlet to the flow distributer.

In another aspect combinable with any of the previous aspects, transporting the refrigerant fluid includes transporting the refrigerant fluid through a closed-circuit refrigeration system that is integrated with the open-circuit refrigeration system.

Another aspect combinable with any of the previous aspects further includes transporting the refrigerant fluid through a liquid separator having an inlet, a vapor- side outlet, and a liquid-side outlet.

Another aspect combinable with any of the previous aspects further includes transporting the refrigerant fluid to a compressor of the closed-circuit refrigeration system, the compressor having a compressor inlet coupled to the vapor-side outlet and having a compressor outlet; and transporting the refrigerant fluid to a condenser having a condenser inlet coupled to the compressor outlet and having a condenser outlet coupled to an inlet of the receiver to condense a superheated vapor at the condenser inlet by removing heat from the refrigerant fluid.

Another aspect combinable with any of the previous aspects further includes receiving refrigerant fluid from the receiver by a recuperative heat exchanger that has a first fluid path that receives the refrigerant fluid from the receiver and a second fluid path that receives refrigerant vapor from the vapor-side outlet, with the second fluid path providing thermal contact between the refrigerant fluid leaving the receiver and refrigerant vapor passing through the recuperative heat exchanger.

Another aspect combinable with any of the previous aspects further includes evaporating any remaining refrigerant liquid in the recuperative heat exchanger prior to the inlet of the compressor.

Another aspect combinable with any of the previous aspects further includes transporting refrigerant fluid from the liquid side outlet of the liquid separator to a secondary inlet of an ejector that further has a primary inlet and an outlet, with the primary inlet fluidly coupled to receive refrigerant from the receiver, and the outlet fluidly coupled to deliver refrigerant fluid to the inlet of the liquid separator.

Another aspect combinable with any of the previous aspects further includes pumping, with the ejector, a secondary refrigerant fluid flow received by the secondary inlet from the liquid side outlet using energy of a primary refrigerant flow from the receiver outlet.

Another aspect combinable with any of the previous aspects further includes pumping, with a pump, refrigerant liquid from the liquid-side outlet of the liquid separator to an inlet of the gated evaporator.

The above aspects or other aspects of the disclosed aspects may include one or more of the following advantages.

The aspects enable cooling of large loads and high heat loads that are also highly temperature sensitive with an undersized cooling system, i.e., a cooling system that has a cooling capacity that is less than the expected cooling capacity for all of the heat loads, and yet which still overcomes some of the problems associated with the conventional closed-cycle refrigeration systems. This undersized cooling system can comprise an open-circuit refrigeration system or a closed-circuit refrigeration system or an open-circuit refrigeration system integrated with a closed-circuit refrigeration system. The details of one or more embodiments are set forth in accompanying drawings and the description below. Other features and advantages will be apparent from the description, drawings, and claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an example of a thermal management system (TMS) that includes an open-circuit refrigeration system (OCRS) according to the present disclosure.

FIG. 2 is a schematic diagram of an example implementation of a gated evaporator implemented in example embodiments of a TMS according to the present disclosure.

FIGS. 3 A and 3B are flow diagrams of cooling initiation processes for a gated evaporator according to the present disclosure.

FIGS. 4-6 are schematic diagrams of example implementations of a TMS that includes at least one of an OCRS and a closed-circuit refrigeration system (CCRS) according to the present disclosure.

FIG. 7 is a block diagram of an example control system (or controller) for a TMS according to the present disclosure.

FIG. 8 is a schematic diagram of an example of a TMS that includes a power generation apparatus.

FIG. 9 is a schematic diagram of an example of directed energy system that includes a TMS.

DETAILED DESCRIPTION

Cooling of large loads and high heat loads that are also highly temperature sensitive can present a number of challenges. On one hand, such loads generate significant quantities of heat that is extracted during cooling. In conventional closed- cycle refrigeration systems, cooling high heat loads typically involves circulating refrigerant fluid at a relatively high mass flow rate. However, closed-cycle system components that are used for refrigerant fluid circulation - including large compressors to compress vapor at a low pressure to vapor at a high pressure and condensers to remove heat from the compressed vapor at the high pressure and convert to a liquid- are heavy and consume significant power. As a result, many closed-cycle systems are not well suited for deployment in mobile platforms - such as on small vehicles or in space - where size and weight constraints may make the use of large compressors and condensers impractical.

On the other hand, temperature sensitive loads such as electronic components and devices may require temperature regulation within a relatively narrow range of operating temperatures. Maintaining the temperature of such a load to within a small tolerance of a temperature set point can be challenging when a single-phase refrigerant fluid is used for heat extraction, since the refrigerant fluid itself will increase in temperature as heat is absorbed from the load.

Directed energy systems that are mounted to mobile vehicles, such as trucks, or that exist in space may present many of the foregoing operating challenges, as such systems may include high heat loads and temperature sensitive components that require precise cooling during operation in a relatively short time. The thermal management systems disclosed herein, while generally applicable to the cooling of a wide variety of heat loads, are particularly well suited for operation with such directed energy systems.

In some cases, the TMS may be specified to cool two different kinds of heat loads - high heat loads (e.g., highly temperature sensitive components) operative for short periods of time and low heat loads (relative to the high heat loads) operative continuously or for relatively long periods (relative to the high heat loads). However, to specify a refrigeration system for the high heat load may result in a relatively large and heavy refrigeration system with a concomitant need for a large and heavy power system to sustain operation of the refrigeration system.

For cooling of large heat loads and high heat loads that are also highly temperature sensitive using conventional refrigeration systems would require use of closed-cycle system components such as relatively large and heavy compressors to compress vapor at a low pressure to vapor at a high pressure and relatively large and heavy condensers to remove heat from the compressed vapor. In addition to being large and heavy, these components typically consume significant amounts of electrical power.

At the same time, the disclosed TMS may be undersized for the given application. That is, the refrigerant flow rate is less than the required refrigerant for a given amount of refrigeration over a specified period of operation. Whereas conventional refrigeration systems would be designed for the maximum flow rate needed for refrigeration, the systems and methods disclosed herein use modified evaporator designed, coupled with refrigerant switching to provide refrigeration for heat loads to maintain temperature of those heat loads with defined temperature ranges.

In some aspects, “refrigeration” as used in the present disclosure can mean a system (or multiple systems fluidly coupled) that operates to generate a purposeful change of a characteristic of a coolant (e.g., a refrigerant fluid) to effectuate or increase heat transfer between two mediums (one of which can be the coolant). The purposeful change of the characteristic can be, for example, a change in pressure (e.g., depressurization) of a pressurized coolant though an expansion valve. In some embodiments, the change in pressure can include a phase change of the coolant, such as a liquid-to-gas phase change (e.g., endothermic vaporization). In some embodiments, pressurization of the refrigerant can be performed by a powered (e.g., electrically or otherwise) component, such as (but not limited to) a compressor. In some embodiments, pressurization can be performed as part of the refrigeration cycle (e.g., a closed-cycle refrigeration process in which gaseous refrigerant is substantially or completely recycled and compressed into a liquid state) or prior to use (e.g., storing pre-compressed liquid refrigerant for later use in an open-cycle refrigeration process in which a reserve of liquid refrigerant is used but substantially not recycled). In some embodiments, the phase change can be driven by heating a liquid refrigerant with a very low boiling point (e.g., ammonia as used in an absorption-type refrigeration cycle).

Referring now to FIG. 1, a thermal management system (TMS) 100 includes an open circuit refrigeration system (OCRS) 5 that utilizes one or more a gated (i.e., Gatling-type) evaporators 116 (herein referred to as an “evaporator 116” unless otherwise noted) to cool one or more heat loads 118. The OCRS 5 includes a receiver 110 having a receiver inlet 109 and receiver outlet 111 and storing a refrigerant fluid 1, an optional solenoid valve 112 having an inlet 113 and an outlet 115, a flow control device 114 (e.g., an expansion valve 114), the evaporator 116 having an inlet 121 and an outlet 123, and a solenoid valve 16 having an inlet 17 and an outlet 19. The aforementioned components of OCRS 5 are interconnected by one or more conduit sections to form an open circuit refrigerant fluid path. An optional flow control device 12 having inlet 13 and outlet 15 and optional check valve 14 are positioned along the gas flow path between the optional gas receiver 10 and the receiver 110.

As will be discussed below in FIG. 2, the gated or “Gatling-type” evaporator 116 is an evaporator that has multiple evaporator sections, and the TMS 100 controls which evaporator sections, and hence, heat loads, receive refrigerant fluid 1 at a given interval of time. For a TMS 100 such as in FIG. 1, the gated or Gatling type evaporator 116 can be used for cooling high heat loads 118 when there are more high heat loads 118 available for powering than a total amount of available power. Generally, the OCRS 5 will deliver as much refrigerant fluid 1 as needed to cool the designed-for-total number of high heat loads 118 for the TMS 100.

However, when the power requirements of the total number of high heat loads 118, ‘g,’ is higher than available power, the TMS 100 is configured to cool ‘g - k’ powered heat loads 118, where ‘g’ is the total number of high heat loads 118 and ‘k’ is a number of high heat loads 118 that are off, i.e., not powered nor outputting heat. Thus, one or more of the high heat loads 118 thermally coupled to evaporator 116 are unpowered high heat loads and remaining ones of the heat loads 118 are powered high heat loads.

The evaporator 116 is referred to as a Gatling evaporator because its principal of operation is somewhat analogous or reminiscent of a Gatling gun. The Gatling gun's operation centered on a cyclic multi-barrel design which facilitated cooling and synchronized the firing-reloading sequence. As the hand wheel is cranked, the barrels rotate clockwise and each barrel sequentially loads a single cartridge from a top- mounted magazine, fires off the shot when it reaches a set position (usually at 4 o'clock), then ejects the spent casing out of the left side at the bottom, after which the barrel is empty and allowed to cool until rotated back to the top position and gravity- fed another new round. This configuration eliminated the need for a single reciprocating bolt design and allowed higher rates of fire to be achieved without the barrels overheating quickly.

The gated or Gatling type evaporator 116 operates in a somewhat analogous or similar manner, by distributing the inlet refrigerant stream over fewer than the total number of evaporator sections that comprise the gated evaporator 116 as discussed in FIG. 2. Evaporator 116 can be implemented in a variety of ways. In general, evaporator 116 functions as a heat exchanger, providing thermal conductive and/or convective contact between the refrigerant fluid 1 and the high heat loads 118 (and/or other heat loads as described herein). Typically, evaporator 116 allows streams of refrigerant fluid 1 to flow through the evaporator 116 and absorb heat from the heat loads 118.

In this example, one or more heat loads 118 can be considered high heat loads that are in thermal conductive and/or convective contact or in proximity with the evaporator section 116. OCRS 5 optionally includes gas receiver 10 with the outlet 11 fluidly coupled to the inlet 109 of the receiver 110 via conduit, such that a gas flow path extends between the gas receiver 10 and the receiver 110 (that stores the refrigerant fluid 1). The optional flow control device 12 having inlet 13 and outlet 15, as well as the optional check valve 14 are positioned along the gas flow path between the optional gas receiver 10 and the receiver 110.

Receiver 110 is typically implemented as an insulated vessel that stores a refrigerant fluid at relatively high pressure. When ambient temperature is very low and, as a result, pressure in the receiver 110 is low and insufficient to drive refrigerant fluid flow through the TMS 100, gas from gas receiver 10 can be directed into receiver 110. The gas compresses liquid refrigerant fluid 1 in receiver 110, maintaining the liquid refrigerant fluid 1 in a sub-cooled state, even when ambient temperature and the temperature of the liquid refrigerant fluid are relatively high. Receiver 110 can also include insulation applied around the receiver 110 and a heater to reduce thermal losses.

In some aspects, receiver 110 includes the inlet 109 and the outlet 111, and may include an optional pressure relief valve. To charge receiver 110, refrigerant fluid is typically introduced into receiver 110 via the inlet 109, and this can be done, for example, at service locations. Operating in the field the refrigerant exits receiver 110 through outlet 111 that is connected to conduit. In case of emergency, if the fluid pressure within receiver 110 exceeds a pressure limit value, a pressure relief valve opens to allow a portion of the refrigerant fluid to escape through valve to reduce the fluid pressure within receiver 110. Receiver 110 is typically implemented as an insulated vessel that stores a refrigerant fluid at relatively high pressure. Receiver 110 can also include insulation applied around the receiver to reduce thermal losses.

In general, receiver 110 can have a variety of different shapes. In some embodiments, for example, the receiver is cylindrical. Examples of other possible shapes include, but are not limited to, rectangular prismatic, cubic, and conical. In certain embodiments, receiver 110 can be oriented such that outlet 111 is positioned at the bottom of the receiver 110. In this manner, the liquid portion of the refrigerant fluid 1 within receiver 110 is discharged first through outlet 111, prior to discharge of refrigerant vapor. In certain embodiments, the refrigerant fluid 1 can be an ammonia- based mixture that includes ammonia and one or more other substances. For example, mixtures can include one or more additives that facilitate ammonia absorption or ammonia burning.

During operation of OCRS 5, cooling can be initiated by a variety of different mechanisms. In some embodiments, for example, OCRS 5 includes a temperature sensor attached to heat load 22 (as will be discussed subsequently) or to certain of heat loads 118. When the temperature of heat load 22 exceeds a certain temperature set point (i.e., threshold value), a control system 999 (described in additional detail below) connected to the temperature sensor can initiate cooling of heat load 22. Alternatively, in certain embodiments, OCRS 5 operates essentially continuously - provided that the pressure within receiver 110 is sufficient - to cool heat loads 118. As soon as receiver 110 is charged with refrigerant fluid, refrigerant fluid is ready to be directed into evaporator 116 to cool heat loads 118. In general, cooling is initiated when a user of the system or the heat load issues a cooling demand.

The TMS 100, as all disclosed embodiments, may also include a control system (or controller) 999 (see FIG. 7 for an exemplary embodiment) that produces control signals (based on sensed thermodynamic properties) to control operation of one or more of the various devices, e.g., optional solenoid control valve 112, expansion valve 114, etc., as needed, as well as to control operation of a motor of a compressor 104, a fan 108, or other components in other example implementations of a TMS. Control system 999 may receive signals, process received signals and send signals (as appropriate) from/to the sensors and control devices to operate the TMS 100.

The term “control system,” as used herein, can refer to an overall system that provides control signals and receives feedback data from unit controllers, such as unit controllers (e.g., programmable logic controllers, motor controllers, variable frequency drives, actuators). In some aspects, the control system includes the overall system and the unit controllers. In some aspects, a control system simply refers to as a single unit controller or a network of two or more individual unit controllers that communicate directly with each other (rather than with an overall system.

The process streams (e.g., refrigerant flows, ambient airflows, other heat exchange fluid flows) in a TMS according to the present disclosure, as well as process streams within any downstream processes with which the TMS is fluidly coupled, can be flowed using one or more flow control systems (e.g., that include the control system 999) implemented throughout the system. A flow control system can include one or more flow pumps, fans, blowers, or solids conveyors to move the process streams, one or more flow pipes through which the process streams are flowed and one or more valves to regulate the flow of streams through the pipes, whether shown in the exemplary figures or not. Each of the configurations described herein can include at least one variable frequency drive (VFD) coupled to a respective pump or fan that is capable of controlling at least one fluid flow rate. In some implementations, liquid flow rates are controlled by at least one flow control valve.

In some embodiments, a flow control system can be operated manually. For example, an operator can set a flow rate for each pump or transfer device and set valve open or close positions to regulate the flow of the process streams through the pipes in the flow control system. Once the operator has set the flow rates and the valve open or close positions for all flow control systems distributed across the system, the flow control system can flow the streams under constant flow conditions, for example, constant volumetric rate or other flow conditions. To change the flow conditions, the operator can manually operate the flow control system, for example, by changing the pump flow rate or the valve open or close position.

In some embodiments, a flow control system can be operated automatically. For example, the flow control system can be connected to a computer or control system (e.g., control system 999) to operate the flow control system. The control system can include a computer-readable medium storing instructions (such as flow control instructions and other instructions) executable by one or more processors to perform operations (such as flow control operations). An operator can set the flow rates and the valve open or close positions for all flow control systems distributed across the facility using the control system. In such embodiments, the operator can manually change the flow conditions by providing inputs through the control system. Also, in such embodiments, the control system can automatically (that is, without manual intervention) control one or more of the flow control systems, for example, using feedback systems connected to the control system. For example, a sensor (such as a pressure sensor, temperature sensor or other sensor) can be connected to a pipe through which a fluid flows. The sensor can monitor and provide a flow condition (such as a pressure, temperature, or other flow condition) of the process stream to the control system. In response to the flow condition exceeding a threshold (such as a threshold pressure value, a threshold temperature value, or other threshold value), the control system can automatically perform operations. For example, if the pressure or temperature in the pipe exceeds the threshold pressure value or the threshold temperature value, respectively, the control system can provide a signal to the pump to decrease a flow rate, a signal to open a valve to relieve the pressure, a signal to shut down process stream flow, or other signals.

Upon initiation of a cooling operation, refrigerant fluid 1 from receiver 110 is discharged from the receiver outlet 111 and through optional solenoid valve 112 if present. As discussed above, the driving force for the transport of refrigerant fluid 1 through OCRS 5 is the pressure within receiver 110. Refrigerant fluid is transported through conduit to expansion valve 114, which directly or indirectly controls vapor quality (see discussion below) at the evaporator outlet 123. It should be understood that more generally, expansion valve 114 can be implemented as any component or device that performs the functional steps described below and provides for vapor quality control at the evaporator outlet 123.

Once inside the expansion valve 114, the refrigerant fluid 1 undergoes constant enthalpy expansion from an initial pressure pr (i.e., the receiver pressure) to an evaporation pressure p _e at the outlet 119 of the expansion valve 114. In general, the evaporation pressure p _e depends on a variety of factors, most notably the desired temperature set point value (i.e., the target temperature) at which each of the heat loads 118 are to be maintained and the heat input generated by the heat loads 118.

The initial pressure in the receiver 110 tends to be in equilibrium with the surrounding temperature and is different for different refrigerant fluids. The pressure in the evaporator 116 depends on the evaporating temperature, which is lower than the heat load temperature and is defined during design of the system. The TMS 100 is operational as long the receiver-to-evaporator pressure difference is sufficient to drive adequate refrigerant fluid flow through the expansion valve 114.

After undergoing constant enthalpy expansion in the expansion valve 114, the liquid refrigerant fluid is converted to a mixture of liquid and vapor phases at the temperature of the fluid and evaporation pressure p _e . This two-phase refrigerant fluid mixture is transported to evaporator 116.

When the two-phase mixture of refrigerant fluid is directed into evaporator 116, the liquid phase absorbs heat from heat loads 118, driving a phase transition of the liquid refrigerant fluid into the vapor phase. Because this phase transition occurs at (nominally) constant temperature, the temperature of the refrigerant fluid mixture within evaporator 116 remains unchanged, provided at least some liquid refrigerant fluid remains in evaporator 116 to absorb heat.

Further, the constant temperature of the refrigerant fluid mixture within evaporator 116 can be controlled by adjusting the pressure p _e of the refrigerant fluid, since adjustment of p _e changes the boiling temperature of the refrigerant fluid. Thus, by regulating the refrigerant fluid pressure p _e upstream from evaporator 116 (e.g., using flow control device 16), the temperature of the two-phase refrigerant fluid mixture within evaporator 116 (and, nominally, the temperature of heat loads 118) can be controlled to match a specific temperature set-point value for each of the heat loads 118, ensuring that each of the heat loads 118 is maintained at, or very near, its targeted temperature.

The pressure drop across the evaporator 116 causes drop of the temperature of the refrigerant mixture (which is the evaporating temperature), but still the evaporator 116 can be configured to maintain the heat loads temperatures within in set tolerances.

In some embodiments, for example, the evaporation pressure of the refrigerant fluid can be adjusted by flow control device 16 to ensure that the temperature of heat loads 118 is maintained to within ± 5 degrees C (e.g., to within ± 4 degrees C, to within ± 3 degrees C, to within ± 2 degrees C, to within ± 1 degree C) of the temperature set point value for heat loads 118.

As discussed above, within evaporator 116, a portion of the liquid refrigerant in the two-phase refrigerant fluid mixture is converted to refrigerant vapor by undergoing a phase change. As a result, the refrigerant fluid mixture that emerges from evaporator 116 has a higher vapor quality (i.e., the fraction of the vapor phase that exists in refrigerant fluid mixture) than the refrigerant fluid mixture that enters evaporator 116.

As the refrigerant fluid mixture emerges from evaporator 116, a portion of the refrigerant fluid can optionally be used to cool one or more additional thermal loads (not shown). Typically, for example, the refrigerant fluid that emerges from evaporator 116 is nearly in the vapor phase. The refrigerant fluid vapor (or, more precisely, high vapor quality fluid vapor) can be directed into a heat exchanger (not shown) coupled to another heat load, and can absorb heat from additional heat loads during propagation through the heat exchanger.

The two-phase refrigerant fluid mixture emerging from evaporator 116 is transported through conduit to flow control device 16, which directly or indirectly controls the upstream pressure, that is, the evaporating pressure p _e in the system.

After passing through flow control device 16, the vapor component of the two-phase refrigerant fluid mixture is discharged as exhaust through an exhaust line 20 of OCRS 5. Refrigerant vapor discharge can occur directly into the environment surrounding OCRS 5. Alternatively, in some embodiments, the refrigerant vapor can be further processed; various features and aspects of such processing are discussed below.

It should be noted that the foregoing steps, while discussed sequentially for purposes of clarity, occur simultaneously and continuously during cooling operations. In other words, refrigerant vapor is continuously being discharged from receiver 110, refrigerant fluid mixture undergoes continuous expansion in expansion valve 114, flowing continuously through evaporator 116 and flow control device 16, and being discharged from OCRS 5, while heat loads 118 are being cooled.

As discussed above, during operation of OCRS 5, as refrigerant fluid 1 is drawn from receiver 110 and used to cool heat loads 118, the pressure driving the refrigerant fluid in receiver 110 through the system can be maintained at a constant value for an extended period of operation by introducing gas from optional gas receiver 10 into receiver 110. In systems where a common receiver is charged with both refrigerant fluid 1 and gas (as described above) or when optional gas receiver 10 is undercharged initially with gas, the period during which constant pressure can be maintained in receiver 110 may be compromised.

If the pressure within receiver 110 falls sufficiently, the capacity of OCRS 5 to maintain a particular temperature set point value for heat loads 118 may be compromised. Therefore, the pressure in the receiver 110, in the optional gas receiver 10, or the pressure drop across the expansion valve 114 (or any related refrigerant fluid pressure or pressure drop in OCRS 5) can be measured and used to adjust operation of the expansion valve 114.

In addition, one or more measured pressure values can provide an indicator of the remaining operational time. An appropriate warning signal can be issued (e.g., by a control system 999) to indicate that in certain period of time, the system may no longer be able to maintain adequate cooling performance; operation of the system can even be halted if the pressure in receiver 110 (or any other measured pressure value in OCRS 5) reaches a low-end threshold value.

It should be noted that while in FIG. 1 only a single receiver 110 is shown, in some embodiments, OCRS 5 can include multiple receivers to allow for operation of the system over an extended time period. Each of the multiple receivers 110 can supply refrigerant fluid 1 to the system to extend to total operating time period. Some embodiments may include plurality of evaporators connected in parallel, which may or may not accompanied by plurality of expansion valves 114 and plurality of evaporators 116.

The expansion valve 114 functions as a flow control device. In general, expansion valve 114 can be implemented as any one or more of a variety of different mechanical and/or electronic devices. For example, in some embodiments, expansion valve 114 can be implemented as a fixed orifice, a capillary tube, and/or a mechanical or electronic expansion valve. In general, fixed orifices and capillary tubes are passive flow restriction elements which do not actively regulate refrigerant fluid flow. Mechanical expansion valves (usually called thermostatic or thermal expansion valves) are typically flow control devices that enthalpically expand a refrigerant fluid from a first pressure to an evaporating pressure, controlling the superheat at the evaporator exit. Mechanical expansion valves generally include an orifice, a moving seat that changes the cross-sectional area of the orifice and the refrigerant fluid volume and mass flow rates, a diaphragm moving the seat, and a bulb at the evaporator exit. The bulb is charged with a fluid and it hermetically fluidly communicates with a chamber above the diaphragm. The bulb senses the refrigerant fluid temperature at the evaporator exit (or another location) and the pressure of the fluid inside the bulb, transfers the pressure in the bulb through the chamber to the diaphragm, and moves the diaphragm and the seat to close or to open the orifice.

Typical electrical expansion valves include an orifice, a moving seat, a motor or actuator that changes the position of the seat with respect to the orifice, a controller, and pressure and temperature sensors at the evaporator exit. The controller calculates the superheat for the expanded refrigerant fluid based on pressure and temperature measurements at the evaporator exit. If the superheat is above a set-point value, the seat moves to increase the cross-sectional area and the refrigerant fluid volume and mass flow rates to match the superheat set-point value. If the superheat is below the set-point value the seat moves to decrease the cross-sectional area and the refrigerant fluid flow rates.

Examples of suitable commercially available expansion valves that can function as expansion valve 114 include, but are not limited to, thermostatic expansion valves available from the Sporlan Division of Parker Hannifin Corporation (Washington, MO) and from Danfoss (Syddanmark, Denmark).

The flow control device 16 generally functions to control the fluid pressure upstream of the flow control device 16. In OCRS 5, flow control device 16 controls the refrigerant fluid pressure upstream from the evaporator 116 and flow control device 16. In general, flow control device 16 can be implemented as a back-pressure regulator (i.e., back-pressure regulator 16) using a variety of different mechanical and electronic devices. Typically, for example, back-pressure regulator 16 is a device that regulates fluid pressure upstream from the regulator. In general, a wide range of different mechanical and electrical/electronic devices can be used as back-pressure regulator. Typically, mechanical back-pressure regulating devices have an orifice and a spring supporting the moving seat against the pressure of the refrigerant fluid stream. The moving seat adjusts the cross-sectional area of the orifice and the refrigerant fluid volume and mass flow rates.

Typical electrical back-pressure regulating devices include an orifice, a moving seat, a motor or actuator that changes the position of the seat in respect to the orifice, a controller, and a pressure sensor at the evaporator exit or at the valve inlet. If the refrigerant fluid pressure is above a set-point value, the seat moves to increase the cross-sectional area of the orifice and the refrigerant fluid volume and mass flow rates to re-establish the set-point pressure value. If the refrigerant fluid pressure is below the set-point value, the seat moves to decrease the cross-sectional area and the refrigerant fluid flow rates.

In general, back-pressure regulators are selected based on the refrigerant fluid volume flow rate, the pressure differential across the regulator, and the pressure and temperature at the regulator inlet. Examples of suitable commercially available backpressure regulators that can function as back-pressure regulator include, but are not limited to, valves available from the Sporlan Division of Parker Hannifin Corporation (Washington, MO) and from Danfoss (Syddanmark, Denmark).

Flow control device 12 is optional and is positioned between optional gas receiver 10 and receiver 110. Without the control device 12, during operation of OCRS 5, gas in optional gas receiver 10 is discharged from optional gas receiver 10 directly into receiver 110 via conduit. With flow control device 12 present in OCRS 5, flow control device 12 functions to regulate the pressure within receiver 110, downstream from the flow control device 12. During operation of OCRS 5, flow control device 12 effectively maintains the total pressure within receiver 110 at or above a target pressure value adequate to provide for sub-cooling of refrigerant fluid 1 in receiver 110, which maintains a particular refrigerant mass flow rate through expansion valve 114 and evaporator 116, and as a result, achieves a desired cooling capacity for one or more thermal loads connected to OCRS 5. If the pressure within receiver 110 falls below the target pressure value, flow control device 12 opens to allow additional gas from optional gas receiver 10 to enter receiver 110, thereby increasing the pressure within receiver 110.

Flow control device 12 effectively functions as a flow regulation device for the gas in optional gas receiver 10, and is implemented as any one or more of a variety of different mechanical and/or electronic devices. One example of such a device is a downstream pressure regulator (DPR), which is a device that regulates fluid pressure downstream from the regulator. Examples of suitable commercially available downstream pressure regulators that can function as flow control device 12 include, but are not limited to, regulators available from Emerson Electric (St. Louis, MO).

A variety of different gases can be introduced into optional gas receiver 31 to control the gas pressure in receiver 110. In general, gases that are used are inert (or relatively inert) with respect to the refrigerant fluid. As an example, when a refrigerant fluid such as ammonia is used, suitable gases that can be introduced into optional gas receiver 10 include, but are not limited to, one or more of nitrogen, argon, xenon, and helium.

Turning now to FIG. 2, and example implementation of evaporator 116 as a gated or Gatling evaporator 116 is shown. In some aspects, light weight and compactness are generally requirements for a TMS to cool electronic components that are, e.g. mobile or space based. In some cases, evaporator sections and/or heat loads are inherently heavy and can carry substantial amount of thermal inertia. The evaporator 116 discussed herein uses this built-in thermal inertia to increase TMS cooling effectiveness and maintain the temperature tolerances in the range when undersized cooling systems are used.

In this example, gated evaporator 116 includes an inlet distributor 206 that takes an inlet stream of refrigerant fluid 1, e.g., from the receiver 110 or expansion valve 114 and distributes the inlet stream over a plurality (i.e., “n”) of control valves 204a through 204n (each having an inlet 201 and an outlet 203) that feed a plurality of evaporator sections 202a through 202n (each having an inlet 205 and an outlet 207). Although shown as positioned upstream of evaporator sections 202a-202n, control valves 204a-204n can be positioned downstream (e.g., at outlets 207) of the corresponding evaporator sections 202a-202n. Gated evaporator 116 also includes an outlet collector 208 that collects the “n” refrigerant streams and combines the collected streams into a single outlet stream of refrigerant fluid 1. The evaporator 116 is configured into the plurality of evaporator sections 202a-202n at least some of which are loaded with individual sets of high heat loads 118 and/or low heat loads 120. Each evaporator section 202a-202n includes a corresponding one of control valves 204a-204b. Some of the evaporators sections 202a-202n include corresponding one or ones of high heat loads 118 and corresponding one or ones of low heat loads 120 attached to the corresponding evaporator section.

The control valves 204a-204n can be any valve that can be closed and opened. The control valves 204a-204n have inlets 201 coupled to outlets of the inlet distributor 81a. Examples of such control valves 204a-204n include expansion valves or any other valve that allows or inhibits refrigerant flow into refrigerant channels of the evaporator sections 202a-202n. The control valves 204a-204n are installed upstream of the evaporator sections 202a-202n in this example, with outlets 203 fluidly coupled to inlets 205 of the evaporator sections 202a-202n.

Each evaporator section 202a-202n further has outlets 207 coupled to inlets of the outlet distributor 208 that receives the “n” outlet refrigerant streams and collects the “n” outlet streams into one composite outlet stream that is fed to an inlet of the back-pressure regulator 16 (for example). In FIG. 2, during operation, the collector 208 can collect “x” less of the number of input steams “n” where “x” is in a range that is at least one and is less than or equal to two less than “n.”

The total cooling capacity of an undersized TMS is lower than the total load applied by all high heat loads 118 and low heat loads 120. If an undersized TMS, as defined herein, would conventionally cool the high heat loads 118 and the low heat loads 120, the heat load demand would exceed the undersized TMS cooling capacity. As a result, an excessive amount of vapor would be formed in refrigerant channels of an evaporator section. Over time of operation, the vapor in the refrigerant channels of the evaporator section would increase, and the heat transfer rates in the enlarged vapor region would abruptly degrade, and as a consequence, the heat transfer area interaction with the two-phase refrigerant would be reduced. The vapor in the channels will produce excessive refrigerant pressure drops, thus degrading the overall cooling capacity of the undersized TMS. If the evaporators 116 are configured to operate in the two-phase region below the critical vapor quality, the negative impact will be even greater. To obviate above problem, the described undersized TMS 100 (and other TMS as described herein) is configured to maintain temperatures of all heat loads within a temperature range. Prior to the engagement with the high heat loads 118 and low heat loads 120, all evaporator sections 202a-202n and all heat loads 118 and 120 are precooled to the low-end of the temperature range. The described, undersized TMS 100 is configured to adequately cool a reduced number (n-x) of the high heat loads 118 and low heat loads 120 and related evaporator sections 202a-202n. The reduced number is equal to the total number of heat loads/evaporator sections “n” minus “x” heat loads.

During engagement, the power input is applied to all high heat loads 118 and low heat loads 120 despite “x” number of evaporator sections 202a-202n not receiving refrigerant. The loads/evaporator sections that do not receive refrigerant will be heated up as much as the thermal inertia permits within the uncooled operational period. Then, at a certain moment, e.g., upon receipt of a control signal 212, the control valves 204a-204n redirect refrigerant flow to a different set of the reduced number of the evaporator sections 202a-202n. Again, the uncooled loads/evaporator sections will be heated up as much as the thermal inertia allows to do that within the uncooled operational period. This process continues during operation of the heat loads, and is periodically undated such that the temperature of the heat loads remains within allowed temperature range.

The purpose of redirecting refrigerant streams or switching sets of cooled/uncooled evaporator sections, is to maximize the time of operation of the heat loads. The switching philosophy is based on using at least one criterion that signals switching of the heat loads. Examples of criteria include determining that an uncooled evaporator section has reached a maximum time period for proper heat load operation. Another criterion is that the uncooled evaporator section has reached the maximum heat load temperature rise during the heat load operation. Another criterion is that the uncooled evaporator section has reaches the maximum evaporator section temperature rise during the heat load operation. Thus, the evaporator 116 can include a timer (not shown, but which can be provide by the control system 999) to measure the criterion of evaporator sections 202a-202n having reached a maximum time period for proper heat load operation or temperature sensors 210 that measure the criterion that the uncooled evaporator section has reached the maximum heat load temperature rise or the criterion that the uncooled evaporator section has reaches the maximum evaporator section temperature rise. Other criteria including combinations of above criteria are possible.

Evaporator sections 202a-202n can be implemented in a variety of ways. In general, an evaporator section functions as a heat exchanger, providing thermal contact between the refrigerant fluid 1 and high heat load(s) 118 and/or low high heat load(s) 120. Typically, an evaporator section includes one or more fluid transport channels extending internally between an inlet and an outlet of the evaporator section, allowing refrigerant fluid to flow through the evaporator section and absorb heat from heat load(s). A variety of different gated evaporators can be used in a TMS according to the present disclosure. In general, an evaporator section of the open-circuit refrigeration systems and the integrated open and closed refrigeration systems disclosed herein can accommodate any number of refrigerant fluid channels (including mini/micro-channel tubes), blocks of printed circuit heat exchanging structures, or more generally, any heat exchanging structures that are used to transport single-phase or two-phase fluids. The evaporator 116 and/or components thereof, such as fluid transport channels, can be attached to the heat loads mechanically, or can be welded, brazed, or bonded to the heat load in any manner. An evaporator section can be fabricated as part of a heat load(s) or otherwise integrated into one or more of the heat loads (e.g., with integrated refrigerant fluid channels). The portion of heat loads and refrigerant fluid channel(s) effectively functions as an evaporator section for an evaporator 116.

Referring now to FIG. 3 A, a flow diagram that depicts a process 300 of cooling high heat loads 118 is shown based on available power is shown. In some process 300 can be used, e.g., by or with the TMS 400 shown in FIG. 4. The process 300 causes (step 302) a precool cycle in which each of the evaporator sections 202a- 202n is precooled to a temperature value at the low end of the temperature range for the most temperature sensitive of the high heat loads 118. The process 300 applies (step 304) power to selected ones of the high heat loads 118 according to high heat load control signals “g” in proximity of the precooled evaporator sections 202a-202n, causing the powered high heat loads 118 to operate under normal circumstances.

However, the process 300 directs (step 306) refrigerant fluid 1 to a selected number (g - k) of the evaporator sections 202a-202n, by opening refrigerant flow to corresponding ones (g - k) of the control valves 204a-204n, while closing others (k) of the control valves 204a-204n and thus inhibiting refrigerant flow to those corresponding evaporator sections. That is, at least one less than the total number of control valves 204a-204n is inhibited from passing refrigerant flow into at least one less of the corresponding evaporator sections 202a-202n. The process 300 monitors each of the evaporator sections 204a-204n according to one or more of above criteria. When the criteria is met (step 308), the process 300 repeats by sending control signals 212 to control operation of a different set of the g - k powered high heat loads 118 (step 310).

Referring now to FIG. 3B, a flow diagram that depicts a process 350 of cooling heat loads 118 (e.g., in TMS 100) or high heat loads 118 and low heat loads 120 (e.g., in TMS 200) is shown. The process 350 causes (step 352) a precool cycle in which each of the evaporator sections 202a-202n is precooled to a temperature value at the low end of the temperature range for the most temperature sensitive of the high heat loads 118 and the low heat loads 120. The process 350 applies power (step 354 to send high heat load control signals and step 356 to apply power) to all of the high heat loads 118 and the low heat loads 120 in proximity of the precooled evaporator sections 202a-202n, causing the high heat loads 118 and the low heat loads 120 to operate under normal circumstances.

However, the process 350 directs refrigerant (step 358) to a selected number (n-x) of the evaporator sections 202a-202n, by opening refrigerant flow to corresponding ones (n-x) of the control valves 204a-204n, while closing “x” others of the control valves 204a-204n and thus inhibiting refrigerant flow to those corresponding evaporator sections. That is, at least one less than the total number of control valves 204a-204n is inhibited from passing refrigerant flow into at least one less of the corresponding evaporator sections 202a-202n. The process 350 monitors (step 360) each of the evaporator sections 202a-202n according to one or more of above criteria.

As an example, process 350 inhibits refrigerant fluid to an evaporator section that has a high heat load and a low heat load. As the heat loads operate, the heat loads will each begin to rise in temperature. However, due to the thermal inertia of the evaporator section, that heat rise will be somewhat delayed and inhibited. For heat loads and an evaporator section that is not receiving refrigerant, the process 350 determines (step 360) when at least one of above criteria has been met for that evaporator section 84a.

When the criterion has been met for the evaporator section, the process 350 will send (step 362) control signals to a different set of heat load(s) and direct (step 364) refrigerant to a different set of the n-x evaporator sections 202a-202n by causing the control valve and others of the control valves 204a-204n to open, while simultaneously causing one of the remaining control valves 204a-204n to close, by shutting “OFF” the corresponding control valve 204a-204n, and causing the process 350 to repeat (step 364 to step 360) for a different set of one or more control valves 204a-204n and heat loads. The repetition will ensure that each evaporator section is uncooled for no more than “i” sequential cycles, where i is typically one or two, but could be more.

Consider that a particular control valve is next to be shut “OFF” this will result in refrigerant being inhibited from flowing through that associated evaporator section. As a result, the heat loads for that associated evaporator section will begin to rise in temperature. However, due to the thermal inertia of that evaporator section, the heat rise will be somewhat delayed and inhibited. The process 350 continues to monitor each of the evaporator sections 202a-202n and for that evaporator section, the heat rise will be somewhat delayed and inhibited. For heat loads and that evaporator section that now is not receiving refrigerant, the process 350 determines whether at least one of above criteria (step 360) has been met for that evaporator section.

When the criterion has been met for that evaporator section, the process 350 will cause the control valve to open, while simultaneously causing one of the remaining control valves to close, by shutting “OFF” the corresponding, remaining control valve. This process 350 will continue until such time as needed. Any switching paradigm can be used, and will vary according to the nature of the heat loads 118 and 120. In addition, time periods and/or temperature ranges can be different for different ones of the heat loads 118 and 120.

Further still, while in the example above, the process 350 inhibited only one evaporator section from receiving refrigerant at a time, in other embodiments more than one evaporator section can be inhibited from receiving refrigerant at a time, depending on specific design requirements. Generally, when more than one evaporator section is shut off from receiving refrigerant at a time, as the process monitors for one or more criteria being met, the process 350 will direct (step 358) the refrigerant to a different set of ‘n-x’ evaporator sections 202a-202n, upon detecting one of the shutdown evaporator sections having satisfied one or more of the criteria.

The use of the evaporator 116 combined with the process 350 of FIG. 3B, effectively uses the built-in thermal inertia to increase the TMS cooling effectiveness and maintain the temperature tolerances in the range when a undersized cooling system is used.

Referring now to FIG. 4, an example implementation of a TMS 400 that includes an optional OCRS 44 fluidly coupled to a closed-circuit refrigeration system (CCRS) 40 and one or more evaporators 116 is shown. In this example, TMS 400 provides closed-circuit refrigeration for one or more low heat loads 120 over long time intervals and open-circuit refrigeration for refrigeration of one or more high heat loads 118 over short time intervals (relative to the interval of refrigeration of low heat load). More specifically, the TMS 400 includes open-circuit refrigeration system 44, without the optional gas receiver 10 and without the control devices 12 and 16, and further includes a closed-circuit refrigeration system (CCRS) 40.

Optional OCRS 44 includes an open circuit fluid circuit that includes a junction 410 as well as the components/devices of FIG. 1, that is the receiver 110, the optional solenoid valve 112, the expansion valve 114, the evaporator 116, backpressure regulator 16, exhaust 20, and associated conduit. The high heat load 118 is in thermal conductive and/or convective contact with the evaporator 116. The OCRS 44 also includes a suction accumulator 124 having an inlet 125 and a vapor-side outlet 127. In some embodiments of TMS discussed herein, the suction accumulator 124 is replaced by a liquid separator 124 that also includes a liquid-side outlet (described later) and other conventional features such as membranes, coalescing filters, or meshes, etc. (not shown).

The CCRS 40 (implemented within the TMS 400) includes the receiver 110 that includes inlet 109 and outlet 111, the optional solenoid valve 112, the expansion valve 114, the evaporator 116, the suction accumulator 124, a junction 410, a compressor 104 having a compressor inlet 101 and a compressor outlet 103, and a condenser 106 having a condenser inlet 105 and a condenser outlet 107, all of which are fluidly coupled via conduit. A fan 108 that generates a condenser airflow 126 (or pump 108 that generates a condenser liquid flow 126) cools refrigerant in the condenser 106. In this example, one or more low heat loads 120 are also in thermally conductive and/or convective contact with the evaporator 116. The optional solenoid valve 112 can be used when the expansion valve 114 is not configured to completely stop refrigerant flow when the TMS 400 is in an OFF state.

In some implementations of the CCRS 40, an oil is used for lubrication of the compressor 104 and the oil travels with the refrigerant in the closed-circuit portion of the TMS 400. The oil is removed from the refrigerant to be recirculated back to the compressor 104. While not expressly shown, the oil can be removed from the inlet 125 of the suction accumulator 124, within the suction accumulator 124, or elsewhere within the TMS 400. TMS 400 has a mechanism, e.g., a solenoid valve (not referenced) and an orifice, to return oil from the suction accumulator 124 (or a liquid separator), particularly, from the bottom of the suction accumulator 124 to the compressor 104. In addition, the CCRS 40 may include an oil separator (OS, as shown). The OS is disposed in an oil return path from the compressor outlet 103 to the compressor inlet 101.

TMS 400 cools heat loads 118 and 120 (shown with the evaporator 116). The low heat load 120 is a heat load that operates over long (or continuous) time intervals and are cooled by the CCRS 40, whereas the high heat load 118 is a heat load that operates over short intervals of time relative to the operating interval of the low heat load 120.

As shown in this example implementation, TMS 400 includes an optional sensor 408 in communication with the expansion valve 114. For example, the expansion valve 114 can be operated with sensor 408 that controls the expansion valve 114 either directly or through control system 999. The evaporator 116 can operate in two phase (liquid/gas) and superheated regions with controlled superheat. The electronically-controlled expansion valve 114 and the sensor 408 provide a mechanism to measure and control superheat.

As further shown in FIG. 4, TMS 400 can include an optional recuperative heat exchanger 402. In some aspects, implementations of the TMS 400 that include recuperative heat exchanger 402 can improve vapor quality at the evaporator 116 exit because of the presence of the recuperative heat exchanger 402 that evaporates any remaining liquid prior to being fed to the inlet 101 of the compressor 104. In some implementations, the presence of the recuperative heat exchanger 402 can eliminate the need for the suction accumulator 124.

The recuperative heat exchanger 402 is coupled in a first fluid path 404 between the outlet 111 and an inlet 401 and between the inlet 113 and an outlet 405. The recuperative heat exchanger 402 is also coupled in a second fluid path 406 between the outlet 123 and an inlet 403 and between an outlet 407 and the inlet 125 of the suction accumulator 124. The recuperative heat exchanger 402 transfers heat energy from the refrigerant fluid 1 flowing to the suction accumulator 124 to refrigerant fluid 1 upstream from the expansion valve 114. Inclusion of the recuperative heat exchanger 402 can reduce mass flow rate demand and allows operation of evaporator 116 within a threshold of vapor quality. In some examples, the recuperative heat exchanger 402 transfers heat energy from the refrigerant fluid emerging from evaporator 116, and the suction accumulator 124 is not needed. That is, the recuperative heat exchanger 402 obviates the need for the suction accumulator 124. Returning now to FIG. 4, operation of the OCRS 44 is described. When the low heat loads 120 are applied, the TMS 400 is configured to have the CCRS 40 provide refrigeration to ‘n-x’ of the low heat loads 120. In this instance, the control system 999 produces signals to cause the back-pressure regulator 16 to be placed in an OFF state (i.e., closed). With the back-pressure regulator 16 closed, the CCRS 40 provides cooling duty to handle ‘n-x’ of the low loads 120.

In the closed-circuit refrigeration configuration, circulating refrigerant enters the compressor 104 as a saturated or superheated vapor and is compressed to a higher pressure at a higher temperature (a superheated vapor). This superheated vapor is at a temperature and pressure at which it can be condensed in the condenser 106 by either cooling water 126 or cooling air 126 flowing across a coil or tubes in the condenser 106. At the condenser 106, the circulating refrigerant loses heat and thus removes heat from the system, which removed heat is carried away by either the water 126 or air 126 (whichever may be the case) flowing over the coil or tubes, providing a condensed liquid refrigerant.

The condensed and sub-cooled liquid refrigerant fluid 1 is routed into the receiver 110, exits the receiver 110, and enters the expansion valve 114 (if used). The refrigerant fluid is enthalpically expands in the expansion valve 114 and the high pressure sub-cooled liquid refrigerant turns into liquid-vapor mixture at a low pressure and temperature. The temperature of the liquid and vapor refrigerant mixture (evaporating temperature) is lower than the temperature of the low heat load 120. The mixture is routed through coils or tubes in ‘n-x’ of the evaporator sections 202a-202n of the evaporator 116. In the evaporator 116, at least “x” of the evaporator sections 202a-202n, is closed, by closing the corresponding the control valves 204a-204n, while refrigerant is permitted to flow though remaining evaporator sections 202a- 202n. Process 350, e.g., describes an operation of the evaporator sections 202a-202n in conjunction with the control valves 204a-204n.

The heat from the low heat loads 120 in contact with or proximate to the evaporator sections 202a-202n, partially or completely evaporates the liquid portion of the two-phase refrigerant mixture, and may superheat the mixture. The refrigerant leaves the evaporator 116 and enters the suction accumulator 124. The saturated or superheated vapor exits the suction accumulator 124 and enters the compressor 104. The evaporator 116 is where the circulating refrigerant absorbs and removes heat from applied low heat loads 120, which heat is subsequently rejected in the condenser 106 and transferred to an ambient by water 126 or air 126 in the condenser 106. To complete the refrigeration cycle, the refrigerant vapor from the evaporator 116 is stored in the suction accumulator 124 and again a saturated vapor portion of the refrigerant in the suction accumulator 124 is routed back into the compressor 104.

On the other hand, when a high heat loads 118 are applied, a mechanism such as the control system 999 causes the TMS 400 to operate in both a closed- and open- circuit configurations. The closed-circuit portion is similar to that described above, except that the evaporator 116 in this case operates within a threshold of a vapor quality, e.g., the evaporator 116 may operate with a superheat provided that the liquid separator captures incidental non-evaporated liquid, the suction accumulator 124 receives two-phase mixture, and the compressor 104 receives saturated vapor from the suction accumulator 124.

When the TMS 400 operates with the open cycle, this causes the control system 999 to be configured to cause the back-pressure regulator 16 to be placed in an ON position, thus opening the back-pressure regulator 16 to permit the back-pressure regulator 16 to exhaust vapor through the exhaust line 20. The back-pressure regulator 16 maintains a back pressure at an inlet to the back-pressure regulator 16, according to a set point pressure, while allowing the back-pressure regulator 16 to exhaust refrigerant vapor through the exhaust line 20.

The OCRS 44 can operate like a thermal energy storage (TES) system, increasing cooling capacity of the TMS 400 when a pulsing heat load is activated, but without a duty cycle cooling penalty commonly encountered with TES systems. The cooling duty is executed without the concomitant penalty of conventional TES systems provided that the receiver 110 has enough refrigerant charge and the refrigerant flow rate flowing through the evaporator 116 matches the rate needed by (n-x) of the high heat loads 118. The back-pressure regulator 16 exhausts the refrigerant vapor, less the refrigerant vapor recirculated by the compressor 104. The rate of exhaust of the refrigerant vapor through the exhaust line 20 is governed by the set point pressure used at the input to the back-pressure regulator 16. As noted, process 350 describes the operation of the evaporator sections 202a-202n in conjunction with the control valves 204a-204n.

When the high heat loads 118 are no longer in use or their temperatures are reduced, this occurrence is sensed by a sensor (not shown) and signals from the sensor (or otherwise, such as communicated directly by the high heat loads 118) are sent to the control system 999. The control system 999 is configured to partially or completely close the back-pressure regulator 16 by changing the set point pressure (or otherwise), partially or totally closing the exhaust line 38 to reduce or cut off exhaust refrigerant flow through the exhaust line 20. When the high heat load 118 reaches a desired temperature or is no longer being used, the back-pressure regulator 16 is placed in the OFF status and is thus closed, and OCRS 40 continues to operate as needed.

The provision of the OCRS 40 helps to reduce amount of exhausted refrigerant. Generally, the TMS 400 uses the compressor 104 to save, e.g., ammonia, and in general it may not be desirable to shut the compressor 104 off. For instance, the compressor 104 can help to keep a high pressure in the receiver 110 if a head pressure control valve is applied.

On the other hand, in some embodiments, the TMS 400 could be configured to operate in modes where the compressor 104 is turned off and the TMS 400 operates in open-circuit mode only (such as in fault conditions in the circuit or cooling requirements).

As noted, the TMS 400 includes the control system 999 that produces control signals (based on sensed thermodynamic properties) to control operation of the various ones of devices as needed, as well as the compressor 104 and back-pressure regulator 16. Control system 999 may receive signals, process received signals and send signals (as appropriate) from/to the expansion valve 114, the optional solenoid valve 112, and a motor of the compressor 104 changing its speed, shutting compressor 104 off or starting it, etc. As used herein the compressor 104 is, in general, a device that increases the pressure of a gas by reducing the gas’ volume. Usually, the term compressor refers to devices operating at and above ambient pressure, (some refrigerant compressors may operate inducing refrigerant at pressures below ambient pressure, e.g., desalination vapor compression systems employ compressors with suction and discharge pressures below ambient pressure)

Implementations of the TMS 400 that include recuperative heat exchanger 402 can adjust a vapor quality of the refrigerant fluid, as the recuperative heat exchanger 402 is configured to generate a sufficient superheat and is used with the suction accumulator 124. The vapor quality of the refrigerant fluid after passing through evaporator 116 can be controlled either directly or indirectly with respect to a vapor quality set point by the control system 999. The evaporator 116 may be configured to maintain exit vapor quality substantially below the critical vapor quality defined as

Vapor quality is the ratio of mass of vapor to mass of liquid + vapor and is generally kept in a range of approximately 0.5 to almost 1.0; more specifically 0.6 to 0.95; more specifically 0.75 to 0.9 more specifically 0.8 to 0.9 or more specifically about 0.8 to 0.85. “Vapor quality” is thus defined as mass of vapor/total mass (vapor + liquid). In this sense, vapor quality cannot exceed “1” or be equal to a value less than “0.” In practice vapor quality may be expressed as “equilibrium thermodynamic quality” that is calculated as follows:

X = (h - h’)/(h” - h’), where h is specific enthalpy, specific entropy or specific volume, h‘ is of saturated liquid and “ is of saturated vapor. In this case X can be mathematically below 0 or above 1, unless the calculation process is forced to operate differently. Either approach is acceptable.

During operation of the TMS 400, cooling can be initiated by a variety of different mechanisms. In some embodiments, for example, TMS 400 includes temperature sensors attached to heat loads 118 and 120 (as will be discussed subsequently). When the temperature of heat loads 118 and 120 exceeds a certain temperature set point (i.e., threshold value), the control system 999 connected to, e.g., temperature sensors 210, can initiate cooling of heat loads 118 and 120.

Alternatively, in certain embodiments, TMS 400 operates essentially continuously - provided that the refrigerant fluid pressure within receiver 110 is sufficient - to cool low heat loads 120 and a temperature sensor attached to high heat loads 118 will cause the control system 999 to switch in the OCRS 44 when the temperatures of high heat loads 118 exceed temperature set point (i.e., threshold value). As soon as receiver 110 is charged with refrigerant fluid 1, refrigerant fluid 1 is ready to be directed into evaporator 116 to cool heat loads 118 and 120. In general, cooling is initiated when a user of the system or the heat load issues a cooling demand.

Referring now to FIG. 5, an example implementation of a TMS 500 that includes an OCRS 54 fluidly coupled to a CCRS 50 with an ejector assist circuit 52 and one or more evaporators 116 is shown. TMS 500 can also implement the process 300 that applies power to all of the heat loads 118 and 120 in the precooled evaporator sections 202a-202n, causing the heat loads 118 and 120 to operate under normal circumstances. In some aspects, the use of the ejector assist circuit 52 can assist in reducing a power requirement of the TMS 500. Items illustrated and referenced, but not mentioned in the discussion below, are discussed and referenced in FIG. 1 and FIG. 4.

As shown in FIG. 5, the TMS 500 includes the OCRS 54 integrated with the CCRS 50. The OCRS 54 is an ejector assisted open circuit refrigeration system. The CCRS 50 generally, includes ejector assist circuit 52 and a liquid separator 124 with a vapor section 522 and a liquid section 524 rather than a suction accumulator. The CCRS 50 provides cooling for low heat load 120 over long time intervals while the OCRS 54 provides cooling for high heat load 118 over short time intervals, as generally discussed above.

TMS 500 includes the receiver 110 that is configured to store sub-cooled liquid refrigerant, as discussed above, and may include an optional solenoid valve 112 and optional expansion valve 114. Both, either or neither of the optional solenoid valve 112 and the optional expansion valve 114 can be used (i.e., or not used) in example embodiments of the TMS 500.

The TMS 500 includes an ejector 502. The ejector 502 has a primary inlet (i.e., high pressure inlet) 501 that is coupled to the receiver 110 (either directly or through the optional solenoid valve 112 and/or expansion valve 114). Outlet 505 of the ejector 502 is coupled to the inlet 125 of the liquid separator 124 (through a evaporator 116 in this example, as explained more hilly below). The ejector 502 also has a secondary inlet or low-pressure inlet 503 that is coupled to the liquid-side outlet 527 via the evaporator 116. The vapor-side outlet 127 of the liquid separator 124 is coupled to the junction 410 that is coupled to the back-pressure regulator 16. The back-pressure regulator 16 has an outlet (not referenced) that feeds exhaust line 20. The junction 410 is coupled to the inlet 101 of the compressor 104. The outlet 103 of the compressor 104 is coupled to the inlet 105 of the condenser 106.

In some aspects, ejector 502 includes a high-pressure motive nozzle or primary inlet 501, a suction or secondary inlet 503, a secondary nozzle that feeds a suction chamber, a mixing chamber for the primary flow of refrigerant and secondary flow of refrigerant to mix, and a diffuser. In one embodiment, the ejector 502 is passively controlled by built-in flow control. Also, optional flow control devices may be employed upstream of the ejector 502. Liquid refrigerant from the receiver 110 is the primary flow. In the motive nozzle, potential energy of the primary flow is converted into kinetic energy reducing the potential energy (the established static pressure) of the primary flow. The secondary flow from the outlet 123 of the evaporator 116 (or from the liquid outlet 527) has a pressure that is higher than the established static pressure in the suction chamber, and thus the secondary flow is entrained through the suction inlet 503 and the secondary nozzles internal to the ejector 502. The two streams (primary flow and secondary flow) mix together in the mixing chamber. In the diffuser section, the kinetic energy of the mixed streams is converted into potential energy elevating the pressure of the mixed flow liquid/vapor refrigerant that leaves the ejector 502 and is fed to the inlet 121 of the evaporator 116 (or liquid separator 124). In the context of open-circuit refrigeration systems, the use of the ejector 502 allows for recirculation of liquid refrigerant captured by the liquid separator 124 to increase the efficiency of the TMS 500. That is, by allowing for some recirculation of refrigerant, but without the need for a compressor or a condenser, this recirculation reduces the required amount of refrigerant needed for a given amount of cooling of ‘n-x’ high heat loads 118 over given periods of operation.

An evaporator 116 is coupled between the ejector outlet 505 of the ejector 502 and the inlet 125 of the liquid separator 124 in this example ejector assist circuit 52.

In this configuration, an evaporator 116 is coupled between the ejector outlet 505 and the liquid separator inlet 125. The flow control device 130 is coupled between the secondary inlet 503 of the ejector 502 and the liquid-side outlet 527 of the liquid separator 124. The recirculation rate in this example is equal to the vapor quality at the evaporator outlet. The flow control device 130 is optional, and when used, is a fixed orifice device. The expansion valve 114 or other control device can be built in the motive nozzle of the ejector 502 and provides active control of the thermodynamic parameters of refrigerant state at the outlet 123. By placing the evaporator 116 between the outlet 505 of the ejector 502 and the inlet 125 of the liquid separator 124, the necessity of having liquid refrigerant pass through the liquid separator 124 during the initial charging of the evaporator 116 with the liquid refrigerant is avoided. At the same time liquid trapped in the liquid separator 124 may be wasted after the TMS 500 shuts down.

In this example configuration, the recirculation rate is equal to the vapor quality at the outlet 123 of the evaporator 116. The flow control device 530 is optional, and when used, can be a fixed orifice device. The expansion valve 114 or other control device can be built in the motive nozzle of the ejector 502 and provides active control of the thermodynamic parameters of refrigerant state at the outlet 123 of the evaporator 116.

In an alternative example of the ejector assist circuit 52 of the TMS 500, the evaporator 116 can be fluidly coupled such that the inlet 121 is connected to liquid outlet 527 of the liquid separator (e.g., through junction 504) and the outlet 123 is fluidly coupled to the secondary inlet 503 of the ejector 502 (as shown in the dashed line representation of evaporator 116). For example, the evaporator 116 can be coupled to the secondary inlet 503 of the ejector 502 and to junction 504, such that the control device 130 and conduit couple the evaporator 116 to the liquid-side outlet 527 of the liquid separator 124.

During open circuit operation in such a configuration, the ejector 502 again acts as a “pump,” to “pump” a secondary fluid flow, e.g., liquid/vapor from the evaporator 116 using energy of the primary refrigerant flow from the receiver 110.

The evaporator 116 may be configured to maintain exit vapor quality below the critical vapor quality defined as “1 However, the higher the exit vapor quality the better it is for operation of the ejector 502. Vapor quality is the ratio of mass of vapor to mass of liquid + vapor and is generally kept in a range of approximately 0.5 to almost 1.0; more specifically 0.6 to 0.95; more specifically 0.75 to 0.9 more specifically 0.8 to 0.9 or more specifically about 0.8 to 0.85. In such a configuration, refrigerant from receiver 110 enters into the primary inlet 501 of the ejector 502 and through the ejector assist circuit 52, meaning that refrigerant flows from the ejector 502 into liquid separator 124 and flow from the liquid separator 124 is expanded by the flow control device 530 (as an expansion valve) into the evaporator 116, which cools the heat loads 118 and/or 120. The refrigerant is returned to the ejector 502 and to the liquid separator 124, while a vapor fraction of the refrigerant is fed to the compressor 104 and to the condenser 106. The liquid separator 124 is used to insure only vapor exists at the input to the compressor 104. In this embodiment, an optional sensor can be disposed at the outlet 123 of the evaporator 116 and communicably coupled to the flow control device 530 (as an expansion valve). The expansion valve 130 and sensor provide a mechanism to measure and control superheat. Closed circuit and open circuit operate as generally discussed for TMS 500, except for provision of the sensor 932 to measure and control superheat.

Further, in another alternative example of the ejector assist circuit 52 of the TMS 500, dual evaporators 116 can be installed in the ejector assist circuit 52 (i.e., with both the solid line and dashed line representations of the evaporator 116 in FIG.

5 included). In such an example, a evaporator 116 is coupled between outlet 505 of the ejector 502 and inlet 125 to the liquid separator 124 and another evaporator 116 is coupled between an outlet of the flow control device 130 and secondary inlet 503 to the ejector 502. Heat loads 118 and/or 120 are coupled to both evaporators 116. The cooling capacity of this configuration of TMS 500 may not be sensitive to recirculation rate (as compared to other example implementations), which may be beneficial when the heat loads may significantly reduce recirculation rate. An operating advantage of such a configuration is that by using dual evaporators 116, it is possible to run the evaporators 116 combining the features of the configurations mentioned above. Also, in this configuration, at least one evaporator 116 can operate with both high heat load 118 and low heat load 120 if those loads allow for operation in superheated regions.

Further, in another alternative example of the ejector assist circuit 52 of the TMS 500, the evaporator 116 can comprise a single evaporator 116 that is attached downstream from and upstream of the ejector 502.

In this example of the TMS 500, an optional evaporator circuit 56 is fluidly coupled at junction 504 to the ejector assist circuit 52 through optional flow control valve 530 (e.g., expansion valve 530). In this optional circuit 56, a conventional evaporator 516 (e.g., not a gating evaporator) is disposed within exhaust 528 with an inlet 521 coupled to the expansion valve 530 and an outlet 523 with a back-pressure regulator 526. The conventional evaporator 516 is in thermal conductive and/or convective contact with heat load 518. Optionally in the optional evaporator circuit 56 is a sensor communicably coupled to the flow control device 530 (as an expansion valve). The conventional evaporator 516 can operate in a superheated region with controlled superheat by the expansion valve 530, which has a control port that is fed from a sensor. The sensor controls the expansion valve 530 and provides a mechanism to measure and control superheat.

If the optional expansion valve and sensor are not included with the optional evaporator circuit 56, then the conventional evaporator 516 shares the same control device 530, i.e., an expansion valve, as the evaporator 116 (or evaporators 116 in the case of dual evaporators 116). The evaporator(s) 116 operates in two-phase (liquid/gas) and conventional evaporator 516 operates in a superheated region with controlled superheat. In some embodiments, refrigerant flow through the TMS 500 during open- circuit operation is controlled in the OCRS 54 either solely by the ejector 502 and back-pressure regulator 16 or by those components aided by either one or all of the optional solenoid valve 112 and expansion valve 114, depending on requirements of application, e.g., ranges of mass flow rates, cooling requirements, receiver capacity, ambient temperatures, heat load, etc. and the flow control device 530.

While both expansion valve 114 and solenoid valve 112 may not typically be used, in some implementations, either or both would be used and would function as a flow control device(s) to control refrigerant flow into the primary inlet 501 of the ejector 502. In some embodiments, the expansion valve 114 can be integrated with the ejector 502. In various embodiments of the TMS 500, the optional expansion valve 114 may be required under some circumstances where there are or can be significant changes in, e.g., an ambient temperature, which might impose additional control requirements on the TMS 500.

The back-pressure regulator 16 has an outlet (not referenced) that is disposed at the exhaust line 20, and further has an inlet (not referenced) coupled via junction 410 to the vapor-side outlet 127 of the liquid separator 124. The back-pressure regulator 16 functions to control the vapor pressure upstream of the back-pressure regulator 16. In TMS 500, the back-pressure regulator 16 is a control device that controls the refrigerant fluid vapor pressure from the liquid separator 124 and indirectly controls evaporating pressure/temperature when the TMS 500 is operating in open circuit mode. In general, back-pressure regulator 16 can be implemented using a variety of different mechanical and electronic flow regulation devices, as mentioned above. The back-pressure regulator 16 regulates fluid pressure upstream from the regulator, i.e., regulates the pressure at the inlet to the back-pressure regulator 16 according to a set pressure point value.

Regarding closed-circuit refrigeration, the CCRS 50 generally operates as discussed above in FIG. 4, with addition of the circuit 52 provided by the ejector 502, liquid separator 124, and evaporator 116. The CCRS 50 provides cooling for low heat loads 120 over long time intervals. The ejector 502 acts as a “pump,” to “pump” a secondary fluid flow, e.g., liquid/vapor from the evaporator 116 (or to the evaporator 116, or both) using energy of the primary refrigerant flow from the receiver 110.

In some embodiments, refrigerant flow through the ejector assist circuit 52 and OCRS 54, during open-circuit operation, is controlled either solely by the ejector 502 and back-pressure regulator 16 or by those components aided by either one or all of the solenoid valve 112 and expansion valve 114, depending on requirements of application, e.g., ranges of mass flow rates, cooling requirements, receiver capacity, ambient temperatures, thermal load, etc. and the flow control device 530.

While both expansion valve 114 and solenoid valve 112 may not typically be used, in some implementations, either or both would be used and would function as a flow control device(s) to control refrigerant flow into the primary inlet 66a of the ejector 502. In some embodiments, the expansion valve 114 is an expansion valve and can be integrated with the ejector 502. In various embodiments of the TMS 500, the optional expansion valve 530 may be required under some circumstances where there are or can be significant changes in, e.g., an ambient temperature, which might impose additional control requirements on the TMS 500.

The back-pressure regulator 16 has an outlet (not referenced) that is disposed at the exhaust line 20, and further has an inlet (not referenced) coupled via junction 410 to the vapor side outlet 127 of the liquid separator 124. The back-pressure regulator 16 functions to control the vapor pressure upstream of the back-pressure regulator 16.

Some loads require maintaining thermal contact between the loads 118 and evaporator 116 with the refrigerant being in the two-phase region (of a phase diagram for the refrigerant) and, therefore, the flow control device 530 maintains a proper vapor quality at the evaporator outlet 123. Alternatively, a sensor communicating with control system 999 may monitor pressure in the receiver 110, as well as a pressure differential across the expansion valve 114, a pressure drop across the evaporator 116, a liquid level in the liquid separator 124, and power input into electrically actuated heat loads, or a combination of above. In the configuration as shown (e.g., with only the evaporator 116 in solid line representation), the evaporator 116 is coupled between the ejector outlet 505 and the liquid separator inlet 125. The flow control device 530 is coupled between the secondary inlet 503 of the ejector 502 and the liquid side outlet 527 of the liquid separator 124. The evaporator 116 is configured to extract heat from the heat loads 118 and 120 that are in thermal conductive and/or convective contact or in proximity to the evaporator 116.

In TMS 500 in this configuration, the recirculation rate is equal to the vapor quality at the evaporator outlet 123. The flow control device 530 is optional, and when used, can be a fixed orifice device. The expansion valve 114 or other control device can be built in the motive nozzle of the ejector 502 and provides active control of the thermodynamic parameters of refrigerant state at the evaporator outlet 123.

This embodiment of the TMS 500 operates as follows, with the back-pressure regulator 16 in a closed or off position. Refrigerant fluid 1 from the receiver 110 is directed into the ejector 512 (optionally through valve 112 and expansion valve 114) and expands at a constant entropy in the ejector 502 (in an ideal case; in reality the nozzle is characterized by the ejector isentropic efficiency), and turns into a two- phase (gas/liquid) state. The refrigerant in the two-phase state enters the evaporator 116 that provides cooling duty (to ‘n-x’ of heat loads 118 and 120) and discharges the refrigerant in a two-phase state at an exit vapor quality (fraction of vapor to liquid) below a unit vapor quality (“1”). The discharged refrigerant is fed to the inlet 125 of the liquid separator 124, where the liquid separator 124 separates the discharge refrigerant with only or substantially only liquid exiting the liquid separator 124 at the liquid side outlet 527 and only or substantially only vapor exiting the separator 124 at the vapor side outlet 127. The vapor section 522 may contain some liquid droplets since the liquid separator 124 has a separation efficiency below a “unit” separation. The liquid stream exiting at outlet 527 (through junction 504) enters the suction or secondary inlet 505 of the ejector 502. The ejector 502 entrains the refrigerant flow exiting the expansion valve by the refrigerant from the receiver 110. In closed-circuit operation, back-pressure regulator 16 is turned off and vapor from the liquid separator 124 is fed to the compressor 104 and condenser 106, as generally discussed above. In open-circuit operation, back-pressure regulator 16 is turned on and a portion of the vapor is exhausted through exhaust line 20, as generally discussed above.

In TMS 500, by placing the evaporator 116 between the outlet 505 of the ejector 502 and the inlet 125 of the liquid separator 124, TMS 500 avoids the necessity of having liquid refrigerant pass through the liquid separator 124 during the initial charging of the evaporator 116 with the liquid refrigerant. At the same time, liquid trapped in the liquid separator 124 may be wasted after the TMS 500 shuts down.

When the evaporator 116 is fluidly coupled at inlet 121 to the junction 504 and at the outlet 123 to the secondary inlet 503 of the ejector 502, operation may commence as follows. For example, during open-circuit operation, the ejector 502 again acts as a “pump,” to “pump” a secondary fluid flow, e.g., liquid/vapor from the evaporator 116 using energy of the primary refrigerant flow from the receiver 110.

The evaporator 116 may be configured to maintain exit vapor quality below the critical vapor quality defined as “1.” However, the higher the exit vapor quality the better it is for operation of the ejector 502. Vapor quality is the ratio of mass of vapor to mass of liquid + vapor and is generally kept in a range of approximately 0.5 to almost 1.0; more specifically 0.6 to 0.95; more specifically 0.75 to 0.9 more specifically 0.8 to 0.9 or more specifically about 0.8 to 0.85, as discussed above.

The CCRS 50, in this configuration, operates as above, except that refrigerant from receiver 110 enters into the primary inlet 501 of the ejector 502 and through the circuit 52, meaning that refrigerant flows from the ejector 502 into liquid separator 124 and refrigerant flow from the liquid separator 124 is expanded by the flow control device 16 into the evaporator 116, which cools heat load 118. The refrigerant is returned to the ejector 502 and to the liquid separator 26, while a vapor fraction of the refrigerant is fed to the compressor 104 and to the condenser 106, as discussed above. The liquid separator 124 is used to insure only vapor exists at the inlet 101 to the compressor 104.

The OCRS 54 operates as follows. The liquid refrigerant from the receiver 110 (primary flow) is fed to the primary inlet 501 of the ejector 502 and expands at a constant entropy in the ejector 502 (in ideal case; in reality the nozzle is characterized by the isentropic efficiency of the ejector) and turns into a two-phase (gas/liquid) state. The refrigerant in the two-phase state from the ejector 502 enters the liquid separator 124, at inlet port 125 with only or substantially only liquid exiting the liquid separator 124 at the liquid side outlet 527 and only or substantially only vapor exiting the separator 124 at vapor side outlet 127.

The evaporator 116 provides cooling duty and discharges the refrigerant in a two-phase state at relatively low exit vapor quality (low fraction of vapor to liquid, e.g., generally below 0.5) into the secondary inlet 503 of the ejector 502. The ejector 502 entrains the refrigerant flow exiting the evaporator 116 and combines it with the primary flow from the receiver 110. Vapor exits from the vapor side outlet 127 of the liquid separator 124 and is exhausted by the exhaust line 20. The back-pressure regulator 16, regulates the pressure upstream of the regulator 16 so as to maintain upstream refrigerant fluid pressure in TMS 500.

In the case of dual evaporators 116 (as previously described) in TMS 500, such a configuration may not be sensitive to recirculation rates (as compared to single evaporator configurations), which may be beneficial when the heat loads may significantly reduce recirculation rate. An operating advantage of a dual evaporator 116 configuration is that by placing evaporators 116 at both the outlet 505 and the secondary inlet 503 of the ejector 502, it is possible to run the evaporators 116 combining the features of the configurations mentioned above. Also, in this configuration, evaporator 116 (in dashed line) can operate with heat loads 118 and 120 if those loads allow for operation in superheated regions.

Referring now to FIG. 6, an example implementation of a TMS 600 that includes an OCRS 64 fluidly coupled to a CCRS 60 with a pump assist circuit 62 and one or more evaporators 116 is shown. TMS 600 can also implement the processes 300/350 that applies power to all of the heat loads 118 and 120 in the precooled evaporator sections 202a-202n, causing the heat loads 118 and 120 to operate under normal circumstances. In some aspects, the use of the pump assist circuit 62 can assist in reducing a power requirement of the TMS 600. Items illustrated and referenced, but not mentioned in the discussion below, are discussed and referenced in FIG. 1, FIG. 4, and FIG. 5.

As shown in FIG. 6, the TMS 600 includes the OCRS 64 integrated with the CCRS 60. The OCRS 64 is an pump assisted open circuit refrigeration system. The CCRS 50 generally, includes pump assist circuit 52 and liquid separator 124 with a vapor section 522 and liquid section 524 rather than a suction accumulator. The CCRS 60 provides cooling for low heat load 120 over long time intervals while the OCRS 64 provides cooling for high heat load 118 over short time intervals, as generally discussed above.

TMS 600 includes the receiver 110 that is configured to store liquid refrigerant, i.e., subcooled liquid refrigerant, optional solenoid control valve 112, optional expansion valve 114, and a junction 604 that has first and second ports configured as inlets and a third port configured as an outlet. TMS 600 also includes one or more evaporators 116, liquid separator 124, a pump 602 having inlet 601 and outlet 603, back-pressure regulator 16, and exhaust line 20. TMS 600 also includes compressor 104 and the condenser 106 having the outlet 107 coupled to the inlet 109 of receiver 110. The TMS 600 includes pump assist circuit 62 having the junction 604, one or more evaporators 116, the liquid separator 124, and the pump 602.

The junction 604 has the first port coupled to the receiver 110 (e.g., through optional valve 112 and expansion valve 114), the second port as an inlet coupled to the outlet 123 of the evaporator 116 (shown in solid line), and a third port as the outlet coupled to the inlet 125 of the liquid separator 124 (through an optional second evaporator 116).

The liquid separator 124 has the inlet 125, the vapor-side outlet 127 and liquid-side outlet 527. The vapor-side outlet 127 of the liquid separator 124 is coupled via junction 410 to inlet 102 of the compressor 104 that controls a vapor pressure in the evaporator 116 and feeds vapor to the condenser 106. The vapor-side outlet 127 is coupled to one port of the junction 410 that feeds compressor 104 and the back-pressure regulator 16. The back-pressure regulator 16 has an outlet that feeds exhaust line 20. The liquid-side outlet 527 of the liquid separator 124 is coupled to inlet 601 of the pump 602 (as shown in this example).

The liquid separator 124 and pump 602 can be arranged in several example configurations. For example, the liquid separator 124 (e.g., implemented as a flash drum) can have the pump 602 located distal from the liquid-side port 527 as shown in FIG. 6. This configuration potentially presents the possibility of cavitation. To minimize the possibility of cavitation, the pump 602 can be located distal from the liquid-side outlet port 527, but the height at which the inlet 125 is located is higher than conventional. This would result in an increase in liquid pressure at the liquid- side outlet 527 of the liquid separator 124 and concomitant therewith an increase in liquid pressure at the inlet 601 of the pump 602. Increasing the pressure at the inlet 601 to the pump 602 should minimize possibility of cavitation. Another strategy is to locate the pump 602 proximate to or indeed, inside of the liquid-side outlet 527. In addition, the height at which the inlet 125 is located can be adjusted increase liquid pressure at the inlet 601 of the pump 602 further minimizing the possibility of cavitation. Another alternative strategy that can be used for any of the configurations involves the use of a sensor that produces a signal that is a measure of the height of a column of liquid in the liquid separator 124. The signal is sent to the control system 999 that will be used to start the pump 602, once a sufficient height of liquid is contained by the liquid separator 124.

Various types of pumps can be used for pump 602. Exemplary types include gear, centrifugal, rotary vane types. When choosing a pump, the pump should be capable to withstand the expected fluid flows, including criteria such as temperature ranges for the fluids, and materials of the pump should be compatible with the properties of the fluid. A subcooled refrigerant can be provided at the pump outlet 603 to avoid cavitation. To do that a certain liquid level in the liquid separator 124 may provide hydrostatic pressure corresponding to that sub-cooling. The junction 604 can positioned in several example positions in the pump assist circuit 62. For example, one of the inlets and the outlet can be interposed between solenoid valve 112 and expansion valve 114, with its other inlet coupled to the outlet 123 of the evaporator 116 (shown in solid line). As another example, one of the inlets and the outlet interposed between the outlet 119 of the expansion valve 114 and inlet 121 to the evaporator 116 (shown dashed line) or inlet 125 to liquid separator 124, with its other inlet coupled to the outlet 123 of the evaporator 116 (shown in solid line). As another example, if both of the optional solenoid control valve 112 and optional expansion valve 114 are not included, then all of the locations for the junction 604 are, in essence, the same provided that there are no other intervening functional devices between the outlet 111 of the receiver 110 and the inlet of the junction 604.

In TMS 600, refrigerant liquid from the liquid-side outlet 527 of the liquid separator 124 is fed to pump inlet 601 and is pumped from the pump 602 into the inlet 121 of the evaporator 116. Refrigerant exiting from the outlet 123 is fed along with the primary refrigerant flow from the expansion valve 114 back to the liquid separator 124 (through another evaporator 116 as an option as shown). These liquid refrigerant streams from the receiver 110 and the pump 602 are mixed downstream from the expansion device 114. Heat loads 118 and/or 120 are in thermal conductive and/or convective contact with or in proximity to the evaporator 116 (or dual evaporators 116 as shown). The evaporator 116 is configured to extract heat from the heat loads 118 and/or 120 and to control the vapor quality at the outlet 123 of the evaporator 116.

The evaporator 116 is coupled between the pump outlet 603 of the pump 602 and the junction 604 in this example pump assist circuit 62. In an alternative example of TMS 600, there can be dual evaporators 116 (with one shown in solid line in FIG.

6 and another evaporator 116 shown in dashed line as an option). Thus, in this example modification, a first evaporator 116 is coupled between the outlet of the junction 604 and the inlet 125 of the liquid separator 124 (as shown in dashed line) and there is a second evaporator 116 having an inlet 121 that is coupled to the outlet 603 of the pump 602 and having an outlet 123 coupled to a second inlet of the junction 604 (this evaporator 116 being shown in solid line). The liquid separator 124 has the inlet 125, the vapor-side outlet 127 and liquid-side outlet 527. Heat loads 118 and/or 120 are in thermal conductive and/or convective contact or in proximity to both evaporators 116 in this modified example. An operating advantage of this modified example is that by placing evaporators 116 at both the outlet and the second inlet of the junction 604, it is possible to combine heat loads 118 and 120 at both evaporators 116, which requires operation in a two-phase region and which allows operation with superheat.

An operating advantage of the dual evaporator configuration is that it is possible to run the evaporators 116 with changing refrigerant rates through the junction 604 to change at different temperatures or change recirculating rates. By using the evaporators 116, the configuration reduces vapor quality at the outlet 123 of the evaporator 116 (shown in sold line) and thus increases circulation rate, as the pump 602 would be ‘pumping’ less vapor and more liquid. That is, with the evaporator 116 (in solid line) is downstream from the pump 602 and better refrigerant distribution could be provided with this component configuration since liquid refrigerant enters the evaporator 116 (in solid line) rather than a liquid/vapor stream as could be for the evaporator 116 (in dashed line). In addition, some heat loads that may be cooled by an evaporator in the superheated phase region, at the same time do not need to actively control superheat.

Further, in another alternative example of the pump assist circuit 62 of the TMS 600, the evaporator 116 can comprise a single evaporator 116 that is attached downstream from and upstream of the junction 604. For example, as a single evaporator 116, the evaporator 116 has a first inlet 121 that is coupled to the outlet of the junction 604 and a first outlet 123 that is coupled to the inlet 125 of the liquid separator 124. The evaporator 116 also has a second inlet 121 that is coupled to the outlet 603 of the pump 602 and has a second outlet 123 that is coupled to the inlet of the junction 604. The liquid-side outlet 527 of the liquid separator 124 is coupled to the inlet 601 of the pump 602. In this example implementation, optional evaporator circuit 66 is fluidly coupled to the liquid separator 124. For example, as shown, in this optional configuration, the liquid separator 124 is configured to have a second, liquid-side outlet 605 in addition to the inlet 125, the vapor-side outlet 127, and the liquid-side outlet 527. Alternatively, such a function could be provided with another junction (not shown). The second outlet 605 diverts a portion of the liquid exiting the liquid separator 124 into a conventional evaporator 616 (with inlet 621 and outlet 623) that is in thermal contact with heat load 618. The conventional evaporator 616 extracts heat from the heat load 618 and exhausts vapor from exhaust line 630.

Exhaust lines 20 and 630 can be combined or can be separated. As shown in the optional evaporator circuit 66, in the case of exhaust 630 not being combined with exhaust 20, another back-pressure regulator 620 can be placed in the exhaust 630.

The evaporator circuit 66 can cool heat loads in two-phase and superheated regions. The conventional evaporator 616 can be fed a portion of the liquid refrigerant and operate in superheated region without the need for active superheat control. For example, optionally in the optional evaporator circuit 66 is expansion valve 614 and sensor 640. The conventional evaporator 616 operates in a superheated region with controlled superheat by the expansion valve 614, which has a control port that is fed from sensor 640. The sensor 640 controls the expansion valve 614 and provides a mechanism to measure and control superheat.

The sensor 640 disposed proximate to the outlet 623 of the conventional evaporator 616 provides a measurement of superheat, and indirectly, vapor quality. For example, sensor 640 is a combination of temperature and pressure sensors that measures the refrigerant fluid superheat downstream from the heat load 618 and transmits the measurements to the control system 999. The control system 999 adjusts the expansion valve 614 based on the measured superheat relative to a superheat set point value. By doing so, control system 999 indirectly adjusts the vapor quality of the refrigerant fluid emerging from conventional evaporator 616.

In closed-circuit operation, the CCRS 60 operates as follows. The backpressure regulator 16 is placed in an OFF position. The liquid refrigerant from the receiver 110 is fed to the expansion valve 114 (if used) and expands at a constant enthalpy in the expansion valve 114 turning into a two-phase (gas/liquid) mixture.

This two-phase liquid/vapor refrigerant is fed to the inlet 125 of the liquid separator 124 (or in the case of dual evaporators, the evaporator 116 shown in dashed line), where the liquid separator 124 separates the discharge refrigerant with only or substantially only liquid exiting the liquid separator 124 at the liquid-side outlet 527 (or both outlet 527 and outlet 655 in the case of the optional evaporator circuit 616) and only or substantially only vapor exiting the liquid separator 124 at vapor-side outlet 127. The liquid stream exiting at liquid-side outlet 527 enters and is pumped by the pump 602 into the evaporator 116 that provides cooling duty and discharges the refrigerant in a two-phase state at a relatively high exit vapor quality (fraction of vapor to liquid). The discharged refrigerant is fed to the junction 604. Vapor from the vapor-side 127 of the liquid separator 124 is fed to the compressor 104, on to the condenser 106, and back into the receiver 110 for closed circuit operation.

On the other hand, when high heat load 118 is applied, a mechanism such as the control system 999 causes the TMS 600 to operate in both a closed and open cycle configuration. The closed cycle portion would be similar to that described. The OCRS 64 has the control system 999 configured to cause the back-pressure regulator 16 to be placed in an ON position, opening the back-pressure regulator 16 to permit the back-pressure regulator 16 to exhaust vapor through the exhaust line 20. The back-pressure regulator 16 maintains a back-pressure at an inlet to the back-pressure regulator 16, according to a set point pressure, while allowing the back-pressure regulator 16 to exhaust refrigerant vapor to the exhaust line 20.

In OCRS 64, the pump 602 can operate across a reduced pressure differential (pressure difference between inlet 601 and outlet 603 of the pump 602). In the context of open circuit refrigeration systems, the use of the pump 602 allows for recirculation of liquid refrigerant from the liquid separator 124 to enable operation at reduced vapor quality at the evaporator outlet 123, avoiding the discharge of remaining liquid out of the TMS 600 at less than the separation efficiency of the liquid separator 124 allows. This recirculation reduces the required amount of refrigerant needed for a given amount of cooling over a given period of operation. The configuration above reduces the vapor quality at the evaporator inlet 121 and thus may improve refrigerant distribution (of the two-phase mixture) in the evaporator 116.

Generally, and as discussed with reference to FIGS. 4, 5, and 6, by adjusting the pressure p _e of the refrigerant fluid 1, the temperature at which the liquid refrigerant phase undergoes vaporization within evaporator 116 can be controlled. Thus, in general, the temperature of heat loads 118, 120 can be controlled by a device or component of a TMS that regulates the pressure of the refrigerant fluid within evaporator 116. System operating parameters include the superheat and the vapor quality of the refrigerant fluid emerging from evaporator 116.

The vapor quality, which is a number from 0 to 1, represents the fraction of the refrigerant fluid that is in the vapor phase. Considering the high heat load 118 individually, because heat absorbed from heat load 118 is used to drive a constant- temperature evaporation of liquid refrigerant to form refrigerant vapor in an evaporator section of the evaporator 116, it is generally important to ensure that, for a particular volume of refrigerant fluid propagating through evaporator 116, at least some of the refrigerant fluid remains in liquid form right up to the point at which the exit aperture of an evaporator section in the evaporator 116 is reached to allow continued heat absorption from heat load 118 without causing a temperature increase of the refrigerant fluid. If the fluid is fully converted to the vapor phase after propagating only partially through evaporator 116, further heat absorption by the (now vapor-phase) refrigerant fluid within evaporator 116 will lead to a temperature increase of the refrigerant fluid and heat load 118.

On the other hand, liquid-phase refrigerant fluid that emerges from evaporator 116 represents unused heat-absorbing capacity, in that the liquid refrigerant fluid did not absorb sufficient heat from the high heat load 118 to undergo a phase change. To ensure that a TMS operates efficiently, amount of unused heat-absorbing capacity should remain relatively small.

In addition, the boiling heat transfer coefficient that characterizes the effectiveness of heat transfer from the high heat load 118 to the refrigerant fluid is typically very sensitive to vapor quality. When the vapor quality increases from zero to a certain value, called a critical vapor quality, the heat transfer coefficient increases. When the vapor quality exceeds the critical vapor quality, the heat transfer coefficient is abruptly reduced to a very low value, causing dryout within evaporator 116. In this region of operation, the two-phase mixture behaves as superheated vapor.

In general, the critical vapor quality and heat transfer coefficient values vary widely for different refrigerant fluids, and heat and mass fluxes. For all such refrigerant fluids and operating conditions, the systems and methods disclosed herein control the vapor quality at the outlet of the evaporator such that the vapor quality approaches the threshold of the critical vapor quality.

To make maximum use of the heat-absorbing capacity of the two-phase refrigerant fluid mixture for high heat load 118, the vapor quality of the refrigerant fluid emerging from evaporator 116 should nominally be equal to the critical vapor quality. Accordingly, to both efficiently use the heat-absorbing capacity of the two- phase refrigerant fluid mixture and also ensure that the temperature of heat load 118 remains approximately constant at the phase transition temperature of the refrigerant fluid in evaporator 116, the systems and methods disclosed herein are generally configured to adjust the vapor quality of the refrigerant fluid emerging from evaporator 116 to a value that is less than or equal to the critical vapor quality.

Another important operating consideration for a TMS is the mass flow rate of refrigerant fluid within the TMS. A gated evaporator 116 can be configured to provide minimal mass flow rate controlling maximal vapor quality, which is the critical vapor quality. By minimizing the mass flow rate of the refrigerant fluid according to the cooling requirements for high heat loads 118, a TMS operates efficiently. Each reduction in the mass flow rate of the refrigerant fluid (while maintaining the same temperature set point value for high heat loads 118) means that the charge of refrigerant fluid added to receiver 110 initially lasts longer, providing further operating time for a TMS.

Within evaporator 116, the vapor quality of a given quantity of refrigerant fluid varies from an evaporator inlet (where vapor quality is lowest) to an evaporator outlet (where vapor quality is highest). Nonetheless, to realize the lowest possible mass flow rate of the refrigerant fluid within the system, the effective vapor quality of the refrigerant fluid within evaporator 116 - even when accounting for variations that occur within evaporator 116 - should match the critical vapor quality as closely as possible.

CCRS power demand and CCRS efficiency are optimal when the evaporating temperature is as high as possible and the condensing pressure is as low as possible. The condenser 106 and evaporator 116 dimensions can be reduced when the evaporating temperature is as low as possible and the condensing pressure is as high as possible.

To ensure that an OCRS operates efficiently and the mass flow rate of the refrigerant fluid is relatively low, and at the same time the temperature of the high heat load 118 is maintained within a relatively small tolerance, a TMS adjusts the vapor quality of the refrigerant fluid emerging from evaporator 116 to a value such that an effective vapor quality within evaporator 116 matches, or nearly matches, the critical vapor quality. At the same time requirements for CCRS efficient operation would be taken into consideration as well. In addition, generally compressors 104 do not work well with liquids at their inlets.

In a TMS, expansion valve 114 is generally configured to control the vapor quality of the refrigerant fluid emerging from evaporator 116. As an example, when expansion valve 114 is implemented as an expansion valve, the expansion valve regulates the mass flow rate of the refrigerant fluid through the valve. In turn, for a given set of operating conditions (e.g., ambient temperature, initial pressure in the receiver, temperature set point value for heat load 118, the vapor quality determines mass flow rate of the refrigerant fluid emerging from evaporator 116.

Expansion valve 114 typically controls the vapor quality of the refrigerant fluid emerging from evaporator 116 in response to information about at least one thermodynamic quantity that is either directly or indirectly related to the vapor quality.

In general, a wide variety of different measurement and control strategies can be implemented in a TMS to achieve the control objectives discussed above. These strategies are presented below. Generally, expansion valve 114 is connected to a measurement device or sensor. The measurement device provides information about the thermodynamic quantities upon which adjustments of the control devices are based. The measurement devices can be implemented in many different ways, depending upon the nature of the control devices.

A variety of different refrigerant fluids can be used in a TMS. Depending on application for both open-circuit refrigeration system operation and closed-circuit refrigeration system operation, emissions regulations and operating environments may limit the types of refrigerant fluids that can be used.

For example, in certain embodiments, the refrigerant fluid can be ammonia having very large latent heat; after passing through the cooling circuit, ammonia refrigerant vapor in the open-circuit operation can be disposed of by incineration, by chemical treatment (i.e., neutralization), and/or by direct venting to atmosphere. In certain embodiments, the refrigerant fluid can be an ammonia-based mixture that includes ammonia and one or more other substances. For example, mixtures can include one or more additives that facilitate ammonia absorption or ammonia burning.

More generally, any fluid can be used as a refrigerant in the open-circuit refrigeration systems disclosed herein, provided that the fluid is suitable for cooling heat loads 118, 120 (e.g., the fluid boils at an appropriate temperature) and, in embodiments where the refrigerant fluid is exhausted directly to the environment, regulations and other safety and operating considerations do not inhibit such discharge.

One example of refrigerant is ammonia. Ammonia under standard conditions of pressure and temperature is in a liquid or two-phase state. Thus, the receiver 110 typically will store ammonia at a saturated pressure corresponding to the surrounding temperature. The pressure in the receiver 110 storing ammonia will change during operation. The use of the expansion valve 114 can stabilize pressure in the receiver 110 during operation, by adjusting the expansion valve 114 (e.g., automatically or by control system 999) based on a measurement of the evaporation pressure (p _e ) of the refrigerant fluid and/or a measurement of the evaporation temperature of the refrigerant fluid.

Control system 999 can adjust expansion valve 114 based on measurements of one or more of the following system parameter values: the pressure drop (pr-pe) across expansion valve 114, the pressure drop across evaporator 116, the refrigerant fluid pressure in receiver 110 (pr), the vapor quality of the refrigerant fluid emerging from evaporator 116 (or at another location in the system), the superheat value of the refrigerant fluid in the system, the evaporation pressure (p _e ) of the refrigerant fluid, and the evaporation temperature of the refrigerant fluid.

To adjust expansion valve 114 based on a particular value of a measured system parameter value, control system 999 compares the measured value to a set point value (or threshold value) for the system parameter, as will be discussed below.

A variety of different refrigerant fluids can be used in any of the OCRS configurations. For open-circuit refrigeration systems in general, emissions regulations and operating environments may limit the types of refrigerant fluids that can be used. For example, in certain embodiments, the refrigerant fluid can be ammonia having very large latent heat; after passing through the cooling circuit, vaporized ammonia that is captured at the vapor port of the liquid separator can be disposed of by incineration, by chemical treatment (i.e., neutralization), and/or by direct venting to atmosphere. Any liquid captured in the liquid separator is recycled back into the OCRSP (either directly or indirectly).

Since liquid refrigerant temperature is sensitive to ambient temperature, the density of liquid refrigerant changes even though the pressure in the receiver 110 remains the same. Also, the liquid refrigerant temperature impacts the vapor quality at the evaporator inlet. Therefore, the refrigerant mass and volume flow rates change and the control devices can be used.

Various combinations of the sensors can be used to measure thermodynamic properties of a TMS that are used to adjust the control devices or pumps discussed above and which signals are processed by the control system 999. Connections (wired or wireless) are provided between each of the sensors and control system 999. In many embodiments, system includes only certain combinations of the sensors (e.g., one, two, three, or four of the sensors) to provide suitable control signals for the control devices.

FIG. 7 shows the control system 999 that includes a processor 702, memory 704, storage 706, and I/O interfaces 708, all of which are connected/coupled together via a bus 710. Any two of the optional devices, as pressure sensors, upstream and downstream from a control device, can be configured to measure information about a pressure differential pr-pe across the respective control device and to transmit electronic signals corresponding to the measured pressure from which a pressure difference information can be generated by the control system 999. Other sensors such as flow sensors and temperature sensors can be used as well. In certain embodiments, sensors can be replaced by a single pressure differential sensor, a first end of which is connected adjacent to an inlet and a second end of which is connected adjacent to an outlet of a device to which differential pressure is to be measured, such as the evaporator. The pressure differential sensor measures and transmits information about the refrigerant fluid pressure drop across the device, e.g., the evaporator 116.

Temperature sensors can be positioned adjacent to an inlet or an outlet of e.g., the evaporator 116 or between the inlet and the outlet. Such a temperature sensor measures temperature information for the refrigerant fluid within evaporator 116 (which represents the evaporating temperature) and transmits an electronic signal corresponding to the measured information. A temperature sensor can be attached to heat loads 118 and/or heat loads 120, which measures temperature information for the load and transmits an electronic signal corresponding to the measured information.

An optional temperature sensor can be adjacent to the outlet of evaporator 116 that measures and transmits information about the temperature of the refrigerant fluid as it emerges from evaporator 116.

In certain embodiments, the systems disclosed herein are configured to determine superheat information for the refrigerant fluid based on temperature and pressure information for the refrigerant fluid measured by any of the sensors disclosed herein. The superheat of the refrigerant vapor refers to the difference between the temperature of the refrigerant fluid vapor at a measurement point in a TMS and the saturated vapor temperature of the refrigerant fluid defined by the refrigerant pressure at the measurement point in a TMS.

To determine the superheat associated with the refrigerant fluid, the system control system 999 (as described) receives information about the refrigerant fluid vapor pressure after emerging from a heat exchanger downstream from evaporator 116, and uses calibration information, a lookup table, a mathematical relationship, or other information to determine the saturated vapor temperature for the refrigerant fluid from the pressure information. The control system 999 also receives information about actual temperature of the refrigerant fluid, and then calculates the superheat associated with the refrigerant fluid as the difference between actual temperature of the refrigerant fluid and the saturated vapor temperature for the refrigerant fluid.

The foregoing temperature sensors can be implemented in a variety of ways in a TMS. As one example, thermocouples and thermistors can function as temperature sensors in a TMS. Examples of suitable commercially available temperature sensors for use in a TMS include, but are not limited to, the 88000 series thermocouple surface probes (available from OMEGA Engineering Inc., Norwalk, CT).

A TMS can include a vapor quality sensor that measures vapor quality of the refrigerant fluid emerging from evaporator 116. Typically, such a sensor is implemented as a capacitive sensor that measures a difference in capacitance between the liquid and vapor phases of the refrigerant fluid. The capacitance information can be used to directly determine the vapor quality of the refrigerant fluid (e.g., by system control system 999). Alternatively, sensor can determine the vapor quality directly based on the differential capacitance measurements and transmit an electronic signal that includes information about the refrigerant fluid vapor quality. Examples of commercially available vapor quality sensors that can be used in a TMS include, but are not limited to, HBX sensors (available from HB Products, Hasselager, Denmark). It should generally understood that the systems disclosed herein can include a variety of combinations of the various sensors described above, and control system 999 can receive measurement information periodically or aperiodically from any of the various sensors. Moreover, it should be understood any of the sensors described can operate autonomously, measuring information and transmitting the information to control system 999 (or directly to the first and/or second control device) or, alternatively, any of the sensors described above can measure information when activated by control system 999 via a suitable control signal, and measure and transmit information to control system 999 in response to activating control signal.

To adjust a control device on a particular value of a measured system parameter value, control system 999 compares the measured value to a set point value (or threshold value) for the system parameter. Certain set point values represent a maximum allowable value of a system parameter, and if the measured value is equal to the set point value (or differs from the set point value by 10% or less (e.g., 5% or less, 3% or less, 1% or less) of the set point value), control system 999 adjusts a respective control device to modify the operating state of a TMS. Certain set point values represent a minimum allowable value of a system parameter, and if the measured value is equal to the set point value (or differs from the set point value by 10% or less (e.g., 5% or less, 3% or less, 1% or less) of the set point value), control system 999 adjusts the respective control device to modify the operating state of a TMS, and increase the system parameter value. The control system 999 executes algorithms that use the measured sensor value(s) to provide signals that cause the various control devices to adjust refrigerant flow rates, etc.

Some set point values represent “target” values of system parameters. For such system parameters, if the measured parameter value differs from the set point value by 1% or more (e.g., 3% or more, 5% or more, 10% or more, 20% or more), control system 999 adjusts the respective control device to adjust the operating state of the system, so that the system parameter value more closely matches the set point value. Optional pressure sensors are configured to measure information about the pressure differential pr-pe across a control device and to transmit an electronic signal corresponding to the measured pressure difference information. Two sensors can effectively measure pr, p _e . In certain embodiments two sensors can be replaced by a single pressure differential sensor. Where a pressure differential sensor is used, a first end of the sensor is connected upstream of a first control device and a second end of the sensor is connected downstream from first control device.

System also includes optional pressure sensors positioned at the inlet and outlet, respectively, of evaporator 116. A sensor measures and transmits information about the refrigerant fluid pressure upstream from evaporator 116, and a sensor measure and transmit information about the refrigerant fluid pressure downstream from evaporator 116. This information can be used (e.g., by a system controller) to calculate the refrigerant fluid pressure drop across evaporator 116. As above, in certain embodiments, sensors can be replaced by a single pressure differential sensor to measure and transmit the refrigerant fluid pressure drop across evaporator 116.

To measure the evaporating pressure (p _e ) a sensor can be optionally positioned between the inlet and outlet of evaporator 116, i.e., internal to evaporator 116. In such a configuration, the sensor can provide a direct a direct measurement of the evaporating pressure.

To measure refrigerant fluid pressure at other locations within system, sensor can also optionally be positioned, for example, in-line along a conduit. Pressure sensors at each of these locations can be used to provide information about the refrigerant fluid pressure downstream from evaporator 116, or the pressure drop across evaporator 116.

It should be appreciated that, in the foregoing discussion, any one or various combinations of two sensors discussed in connection with system can correspond to the first measurement device connected to expansion valve 114, and any one or various combination of two sensors can correspond to the second measurement device. In general, as discussed previously, the first measurement device provides information corresponding to a first thermodynamic quantity to the first control device, and the second measurement device provides information corresponding to a second thermodynamic quantity to the second control device, where the first and second thermodynamic quantities are different, and therefore allow the first and second control device to independently control two different system properties (e.g., the vapor quality of the refrigerant fluid and the heat load temperature, respectively).

In some embodiments, one or more of the sensors shown in system are connected directly to expansion valve 114. The first and second control devices (expansion valve 114 and flow control valve 530 for example), for example, can be configured to adaptively respond directly to the transmitted signals from the sensors, thereby providing for automatic adjustment of the system’s operating parameters. In certain embodiments, the first and/or second control device can include processing hardware and/or software components that receive transmitted signals from the sensors, optionally perform computational operations, and activate elements of the first and/or second control device to adjust the control device in response to the sensor signals.

In addition, control system 999 is optionally connected to expansion valve 114. In embodiments where expansion valve 114 is implemented as a device controllable via an electrical control signal, control system 999 is configured to transmit suitable control signals to the first and/or second control device to adjust the configuration of these components. In particular, control system 999 is configured to adjust expansion valve 114 to control the vapor quality of the refrigerant fluid in a TMS.

During operation of the a TMS, control system 999 typically receives measurement signals from one or more sensors. The measurements can be received periodically (e.g., at consistent, recurring intervals) or irregularly, depending upon the nature of the measurements and the manner in which the measurement information is used by control system 999. In some embodiments, certain measurements are performed by control system 999 after particular conditions - such as a measured parameter value exceeding or falling below an associated set point value - are reached. By way of example, Table 1 summarizes various examples of combinations of types of information (e.g., system properties and thermodynamic quantities) that can be measured by the sensors of system and transmitted to control system 999, to allow control system 999 to generate and transmit suitable control signals to expansion valve 114 and/or other control devices. The types of information shown in Table 1 can generally be measured using any suitable device (including combination of one or more of the sensors discussed herein) to provide measurement information to control system 999.

Table 1

FCM Press Drop = refrigerant fluid pressure drop across first control device

Evap Press Drop = refrigerant fluid pressure drop across evaporator Rec Press = refrigerant fluid pressure in receiver VQ = vapor quality of refrigerant fluid

SH = superheat of refrigerant fluid

Evap VQ = vapor quality of refrigerant fluid at evaporator outlet Evap P/T = evaporation pressure or temperature HL Temp = heat load temperature For example, in some embodiments, expansion valve 114 is adjusted (e.g., automatically or by control system 999) based on a measurement of the evaporation pressure (p _e ) of the refrigerant fluid and/or a measurement of the evaporation temperature of the refrigerant fluid. In certain embodiments, expansion valve 114 is adjusted (e.g., automatically or by control system 999) based on a measurement of the temperature of thermal load 49b.

To adjust any of the control devices, the compressor 104, or the pump 602 based on a particular value of a measured system parameter value, control system 999 compares the measured value to a set point value (or threshold value) for the system parameter. Certain set point values represent a maximum allowable value of a system parameter, and if the measured value is equal to the set point value (or differs from the set point value by 10% or less (e.g., 5% or less, 3% or less, 1% or less) of the set point value), control system 999 adjusts expansion valve 114 to adjust the operating state of the system, and reduce the system parameter value.

Certain set point values represent a minimum allowable value of a system parameter, and if the measured value is equal to the set point value (or differs from the set point value by 10% or less (e.g., 5% or less, 3% or less, 1% or less) of the set point value), control system 999 adjusts expansion valve 114, etc. to adjust the operating state of the system, and increase the system parameter value.

Some set point values represent “target” values of system parameters. For such system parameters, if the measured parameter value differs from the set point value by 1% or more (e.g., 3% or more, 5% or more, 10% or more, 20% or more), control system 999 adjusts expansion valve 114, etc. to adjust the operating state of the system, so that the system parameter value more closely matches the set point value.

Measured parameter values are assessed in relative terms based on set point values (i.e., as a percentage of set point values). Alternatively, in some embodiments, measured parameter values can be accessed in absolute terms. For example, if a measured system parameter value differs from a set point value by more than a certain amount (e.g., by 1 degree C or more, 2 degrees C or more, 3 degrees C or more, 4 degrees C or more, 5 degrees C or more), then control system 999 adjusts expansion valve 114, etc. to adjust the operating state of the system, so that the measured system parameter value more closely matches the set point value. In the foregoing examples, measured parameter values are assessed in relative terms based on set point values (i.e., as a percentage of set point values). Alternatively, in some embodiments, measured parameter values can be in absolute terms. For example, if a measured system parameter value differs from a set point value by more than a certain amount (e.g., by 1 degree C or more, 2 degrees C or more, 3 degrees C or more, 4 degrees C or more, 5 degrees C or more), then control system 999 adjusts expansion valve 114, etc. to adjust the operating state of the system, so that the measured system parameter value more closely matches the set point value.

In certain embodiments, refrigerant fluid emerging from evaporator 116 can be used to cool one or more additional thermal loads. In addition, systems can include a second thermal load connected to a heat exchanger. A variety of mechanical connections can be used to attach second thermal load to heat exchanger, including (but not limited to) brazing, clamping, welding, and any of the other connection types discussed herein.

Heat exchangers include one or more flow channels through which high vapor quality refrigerant fluid flows after leaving evaporator 116. During operation, as the refrigerant fluid vapor phases through the flow channels, it absorbs heat energy from second thermal load, cooling second thermal load. Typically, second thermal load is not as sensitive as thermal load 118 to fluctuations in temperature. Accordingly, while second thermal load is generally not cooled as precisely relative to a particular temperature set point value as thermal loads 120, the refrigerant fluid vapor provides cooling that adequately matches the temperature constraints for second thermal load.

In general, the TMS disclosed herein can include more than one (e.g., two or more, three or more, four or more, five or more, or even more) thermal loads in addition to thermal loads depicted. Each of additional thermal loads can have an associated heat exchanger; in some embodiments, multiple additional thermal loads are connected to a single heat exchanger, and in certain embodiments, each additional thermal load has its own heat exchanger. Moreover, each of additional thermal loads can be cooled by the superheated refrigerant fluid vapor after a heat exchanger attached to the second load or cooled by the high vapor quality fluid stream that emerges from evaporator 116.

Although evaporator 116 and heat exchanger are implemented as separate components, in certain embodiments, these components can be integrated to form a single heat exchanger, with thermal load and second thermal load both connected to the single heat exchanger. The refrigerant fluid vapor that is discharged from the evaporator portion of the single heat exchanger is used to cool second thermal load, which is connected to a second portion of the single heat exchanger.

The vapor quality of the refrigerant fluid after passing through evaporator 116 can be controlled either directly or indirectly with respect to a vapor quality set point by control system 999. In some embodiments, the system includes a vapor quality sensor that provides a direct measurement of vapor quality, which is transmitted to control system 999. Control system 999 adjusts control device depending on configuration to control the vapor quality relative to the vapor quality set point value.

In certain embodiments, the system includes a sensor that measures superheat and indirectly, vapor quality. For example, a combination of temperature and pressure sensors measure the refrigerant fluid superheat downstream from a second heat load, and transmit the measurements to control system 999. Control system 999 adjusts control device according to the configuration based on the measured superheat relative to a superheat set point value. By doing so, control system 999 indirectly adjusts the vapor quality of the refrigerant fluid emerging from evaporator 116.

As the two refrigerant fluid streams flow in opposite directions within recuperative heat exchanger, heat is transferred from the refrigerant fluid emerging from evaporator 116 to the refrigerant fluid entering expansion valve 114. Heat transfer between the refrigerant fluid streams can have a number of advantages. For example, recuperative heat transfer can increase the refrigeration effect in evaporator 116, reducing the refrigerant mass transfer rate implemented to handle the heat load presented by high heat load 118. Further, by reducing the refrigerant mass transfer rate through evaporator 116, amount of refrigerant used to provide cooling duty in a given period of time is reduced. As a result, for a given initial quantity of refrigerant fluid introduced into receiver 110, the operational time over which the system can operate before an additional refrigerant fluid charge is needed can be extended. Alternatively, for the system to effectively cool high heat load 118 for a given period of time, a smaller initial charge of refrigerant fluid into receiver 110 can be used. Because the liquid and vapor phases of the two-phase mixture of refrigerant fluid generated following expansion of the refrigerant fluid in expansion valve 114 can be used for different cooling applications, in some embodiments, the system can include a phase separator to separate the liquid and vapor phases into separate refrigerant streams that follow different flow paths within a TMS. Further, eliminating (or nearly eliminating) the refrigerant vapor from the refrigerant fluid stream entering evaporator 116 can help to reduce the cross-section of the evaporator and improve film boiling in the refrigerant channels. In film boiling, the liquid phase (in the form of a film) is physically separated from the walls of the refrigerant channels by a layer of refrigerant vapor, leading to poor thermal contact and heat transfer between the refrigerant liquid and the refrigerant channels.

Reducing film boiling improves the efficiency of heat transfer and the cooling performance of evaporator 116.

In addition, by eliminating (or nearly eliminating) the refrigerant vapor from the refrigerant fluid stream entering evaporator 116, distribution of the liquid refrigerant within the channels of evaporator 116 can be made easier. In certain embodiments, vapor present in the refrigerant channels of evaporator 116 can oppose the flow of liquid refrigerant into the channels. Diverting the vapor phase of the refrigerant fluid before the fluid enters evaporator 116 can help to reduce this difficulty. In addition to phase separator, or as an alternative to phase separator, in some embodiments the systems disclosed herein can include a phase separator downstream from evaporator 116. Such a configuration can be used when the refrigerant fluid emerging from evaporator is not entirely in the vapor phase, and still includes liquid refrigerant fluid. The foregoing examples of thermal management systems illustrate a number of features that can be included in any of the systems within the scope of this disclosure. In addition, a variety of other features can be present in such systems.

In certain embodiments, refrigerant fluid that is discharged from evaporator 116 and passes through conduit can be directly discharged as exhaust from conduit without further treatment. Direct discharge provides a convenient and straightforward method for handling spent refrigerant, and has added advantage that over time, the overall weight of the system is reduced due to the loss of refrigerant fluid. For systems that are mounted to small vehicles or are otherwise mobile, this reduction in weight can be important.

In some embodiments, however, refrigerant fluid vapor can be further processed before it is discharged. Further processing may be desirable depending upon the nature of the refrigerant fluid that is used, as direct discharge of unprocessed refrigerant fluid vapor may be hazardous to humans and/or may be deleterious to mechanical and/or electronic devices in the vicinity of a TMS. For example, the unprocessed refrigerant fluid vapor may be flammable or toxic, or may corrode metallic device components. In situations such as these, additional processing of the refrigerant fluid vapor may be desirable.

In general, refrigerant processing apparatus can be implemented in various ways. In some embodiments, refrigerant processing apparatus is a chemical scrubber or water-based scrubber. Within apparatus, the refrigerant fluid is exposed to one or more chemical agents that treat the refrigerant fluid vapor to reduce its deleterious properties. For example, where the refrigerant fluid vapor is basic (e.g., ammonia) or acidic, the refrigerant fluid vapor can be exposed to one or more chemical agents that neutralize the vapor and yield a less basic or acidic product that can be collected for disposal or discharged from apparatus.

As another example, where the refrigerant fluid vapor is highly chemically reactive, the refrigerant fluid vapor can be exposed to one or more chemical agents that oxidize, reduce, or otherwise react with the refrigerant fluid vapor to yield a less reactive product that can be collected for disposal or discharged from apparatus. In certain embodiments, refrigerant processing apparatus can be implemented as an adsorptive sink for the refrigerant fluid. Apparatus can include, for example, an adsorbent material bed that binds particles of the refrigerant fluid vapor, trapping the refrigerant fluid within apparatus and preventing discharge. The adsorptive process can sequester the refrigerant fluid particles within adsorbent material bed, which can then be removed from apparatus and sent for disposal.

In some embodiments, where the refrigerant fluid is flammable, refrigerant processing apparatus can be implemented as an incinerator. Incoming refrigerant fluid vapor can be mixed with oxygen or another oxidizing agent and ignited to combust the refrigerant fluid. The combustion products can be discharged from the incinerator or collected (e.g., via an adsorbent material bed) for later disposal.

As an alternative, refrigerant processing apparatus can also be implemented as a combustor of an engine or another mechanical power-generating device.

Refrigerant fluid vapor from conduit can be mixed with oxygen, for example, and combusted in a piston-based engine or turbine to perform mechanical work, such as providing drive power for a vehicle or driving a generator to produce electricity. In certain embodiments, the generated electricity can be used to provide electrical operating power for one or more devices, including high heat load 118. For example, high heat load 118 can include one or more electronic devices that are powered, at least in part, by electrical energy generated from combustion of refrigerant fluid vapor in refrigerant processing apparatus.

The thermal management systems disclosed herein can optionally include a phase separator upstream from the refrigerant processing apparatus.

Particularly during start-up of the systems disclosed herein, liquid refrigerant may be present in conduits because the systems generally begin operation before high heat loads 118 and/or low heat loads 120 are activated. Accordingly, phase separator functions in a manner similar to phase separators to separate liquid refrigerant fluid from refrigerant vapor. The separated liquid refrigerant fluid can be re-directed to another portion of the system, or retained within phase separator until it is converted to refrigerant vapor. By using phase separator, liquid refrigerant fluid can be prevented from entering refrigerant processing apparatus.

In some embodiments, the refrigeration systems disclosed herein can be combined with power systems to form integrated power and thermal systems, in which certain components of the integrated systems are responsible for providing refrigeration functions and certain components of the integrated systems are responsible for generating operating power.

FIG. 8 shows an integrated power and a TMS that includes many features similar to those discussed above with only aspects of an OCRS (e.g., OCRS 5 or other OCRS described herein) shown. In addition, a TMS includes, is coupled to, or is part of an engine 800 with an inlet that receives the stream of waste refrigerant fluid. Engine 800 can combust the waste refrigerant fluid directly, or alternatively can mix the waste refrigerant fluid with one or more additives (such as oxidizers) before combustion. Where ammonia is used as the refrigerant fluid in OCRS 5, suitable engine configurations for both direct ammonia combustion as fuel, and combustion of ammonia mixed with other additives, can be implemented. In general, combustion of ammonia improves the efficiency of power generation by the engine.

The energy released from combustion of the refrigerant fluid can be used by engine 800 to generate electrical power, e.g., by using the energy to drive a generator. The electrical power can be delivered via electrical connection to high heat loads 118 to provide operating power for the load. For example, in certain embodiments, high heat loads 118 include one or more electrical circuits and/or electronic devices, and engine 800 provides operating power to the circuits/devices via combustion of refrigerant fluid. Byproducts 802 of the combustion process can be discharged from engine 800 via exhaust conduit, as shown in FIG. 8.

Various types of engines and power-generating devices can be implemented as engine 800 in a TMS. In some embodiments, for example, engine 800 is a conventional four-cycle piston-based engine, and the waste refrigerant fluid is introduced into a combustor of the engine. In certain embodiments, engine 800 is a gas turbine engine, and the waste refrigerant fluid is introduced via the engine inlet to afterburner of the gas turbine engine. As discussed above, in some embodiments, a TMS can include phase separator (not shown) positioned upstream from engine 140. Phase separator functions to prevent liquid refrigerant fluid from entering engine 800, which may reduce the efficiency of electrical power generation by engine 800.

In certain embodiments, the thermal management systems disclosed herein operate differently at, and immediately following, system start-up, compared to the manner in which the systems operate after an extended running period. Upon startup, the compressor 104 and a device (usually a fan) moving a cooling fluid (usually ambient air) through the condenser 106 are powered. The compressor 104 discharges compressed refrigerant into the condenser 106. The refrigerant is condensed and subcooled in the condenser 106. Liquid refrigerant fluid enters receiver 110 at a pressure and temperature generated by operation of the compressor 104 and condenser 106.

The thermal management systems and methods disclosed herein can be implemented as part of (or in conjunction with) directed energy systems such as high energy laser systems. Due to their nature, directed energy systems typically present a number of cooling challenges, including certain heat loads for which temperatures are maintained during operation within a relatively narrow range.

FIG. 9 shows one example of a directed energy system, specifically, a high energy laser system 900. System 900 includes a bank of one or more laser diodes 902 and an amplifier 804 connected to a power source 906. During operation, laser diodes 902 generate an output radiation beam 908 that is amplified by amplifier 804, and directed as output beam 910 onto a target. Generation of high energy output beams can result in the production of significant quantities of heat. Certain laser diodes, however, are relatively temperature sensitive, and the operating temperature of such diodes is regulated within a relatively narrow range of temperatures to ensure efficient operation and avoid thermal damage. Amplifiers are also temperature-sensitively, although typically less sensitive than diodes.

To regulate the temperatures of various components of directed energy systems such as diodes 902 and amplifier 804, such systems can include components and features of the thermal management systems disclosed herein. In FIG. 19, a portion of evaporator 116 (FIGS. 1, 2, etc.) is coupled to diodes 902, while another portion 24’ of the evaporator 116 is coupled to amplifier 804. The other components of the thermal management systems disclosed herein are not shown for clarity. However, it should be understood that any of the features and components discussed above can optionally be included in directed energy systems. Diodes 902, due to their temperature-sensitive nature, effectively function as a high heat loads 118 in system 900, while amplifier 804 functions as a low heat loads 120.

System 900 is one example of a directed energy system that can include various features and components of the thermal management systems and methods described herein. However, it should be appreciated that the thermal management systems and methods are general in nature, and can be applied to cool a variety of different heat loads under a wide range of operating conditions.

Control system 999 can generally be implemented as any one of a variety of different electrical or electronic computing or processing devices, and can perform any combination of the various steps discussed above to control various components of the disclosed thermal management systems.

Control system 999 can generally, and optionally, include any one or more of a processor (or multiple processors), a memory, a storage device, and input/output device. Some or all of these components can be interconnected using a system bus. The processor is capable of processing instructions for execution. In some embodiments, the processor is a single-threaded processor. In certain embodiments, the processor is a multi-threaded processor. Typically, the processor is capable of processing instructions stored in the memory or on the storage device to display graphical information for a user interface on the input/output device, and to execute the various monitoring and control functions discussed above. Suitable processors for the systems disclosed herein include both general and special purpose microprocessors, and the sole processor or one of multiple processors of any kind of computer or computing device.

The memory stores information within the system, and can be a computer- readable medium, such as a volatile or non-volatile memory. The storage device can be capable of providing mass storage for the control system 999. In general, the storage device can include any non-transitory tangible media configured to store computer readable instructions. For example, the storage device can include a computer-readable medium and associated components, including: magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory including by way of example, semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. Processors and memory units of the systems disclosed herein can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits).

The input/output device provides input/output operations for control system 999, and can include a keyboard and/or pointing device. In some embodiments, the input/output device includes a display unit for displaying graphical user interfaces and system related information.

The features described herein, including components for performing various measurement, monitoring, control, and communication functions, can be implemented in digital electronic circuitry, or in computer hardware, firmware, or in combinations of them. Methods steps can be implemented in a computer program product tangibly embodied in an information carrier, e.g., in a machine-readable storage device, for execution by a programmable processor (e.g., of control system 999), and features can be performed by a programmable processor executing such a program of instructions to perform any of the steps and functions described above. Computer programs suitable for execution by one or more system processors include a set of instructions that can be used directly or indirectly, to cause a processor or other computing device executing the instructions to perform certain activities, including the various steps discussed above.

Computer programs suitable for use with the systems and methods disclosed herein can be written in any form of programming language, including compiled or interpreted languages, and can be deployed in any form, including as stand-alone programs or as modules, components, subroutines, or other units suitable for use in a computing environment.

In addition to one or more processors and/or computing components implemented as part of control system 999, the systems disclosed herein can include additional processors and/or computing components within any of the control device

(e.g., expansion valve 114) and any of the sensors discussed above. Processors and/or computing components of the control devices and sensors, and software programs and instructions that are executed by such processors and/or computing components, can generally have any of the features discussed above in connection with control system 999.

A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other embodiments are within the scope of the following claims.