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 the amount of absorbed thermal energy that the system is designed to handle, the heavier the refrigeration system and the larger the 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 thermal management system includes a closed-circuit refrigerant system (CCRS) configured to circulate a refrigerant fluid. The CCRS includes a compressor having a compressor inlet and a compressor outlet and configured to compress a flow of the refrigerant fluid; a condenser having a condenser inlet and a condenser outlet, with the compressor outlet coupled to the condenser inlet; a receiver configured to store at least a portion of the refrigerant fluid, with the receiver having a receiver inlet and a receiver outlet, with the receiver inlet coupled to the condenser outlet; a pump having a pump inlet coupled to the receiver outlet and having a pump outlet, the pump configured to circulate the refrigerant fluid through at least a portion of the CCRS; a flow control device having an inlet and an outlet, with the inlet coupled to the pump outlet, the flow control device configured to control the flow of the refrigerant fluid to an evaporator; and the evaporator having an evaporator inlet and an evaporator outlet, with the evaporator configured to extract heat from at least one heat load that is in thermal conductive or convective contact with the evaporator.

In an aspect combinable with the example implementation, the thermal management system further includes a control system to perform operations including adjusting operation of at least one of the pump or the compressor based on an ambient temperature of a condensing fluid circulated through the condenser to cool the refrigerant fluid.

In another aspect combinable with any of the previous aspects, the control system performs operations including determining that the ambient temperature is less than a lower threshold and based on the determination, turning off the compressor and turning on the pump.

In another aspect combinable with any of the previous aspects, the control system performs operations including determining that the ambient temperature is greater than an upper threshold; and based on the determination, turning off the pump and turning on the compressor.

In another aspect combinable with any of the previous aspects, the flow control device is an expansion valve that has a valve inlet and a valve outlet, with the valve inlet coupled to the pump outlet. The evaporator inlet is coupled to the valve outlet. The system further includes a suction accumulator having an inlet and a vapor-side outlet, with the inlet coupled to the evaporator outlet and the vapor-side outlet coupled to the compressor inlet.

Another aspect combinable with any of the previous aspects further includes a compressor bypass circuit that has a bypass conduit that fluidly couples the evaporator outlet to the condenser inlet external to the compressor. The control system performs operations including determining that the ambient temperature is less than a lower threshold and based on the determination, turning off the compressor and directing the flow of the refrigerant fluid from the evaporator outlet, through the bypass conduit, and to the condenser inlet. In another aspect combinable with any of the previous aspects, the compressor bypass circuit further incudes a solenoid control valve, a first check valve, and a second check valve. The solenoid control valve is coupled between the vapor-side outlet of the suction accumulator and the compressor inlet. The first check valve is coupled to the outlet of the compressor and the second check valve is coupled to the vapor-side outlet of the suction accumulator.

In an aspect combinable with the example implementation, the condenser includes a subcooler. The condenser condenses at least a portion of the refrigerant fluid to a saturated state or a subcooled state. The subcooler subcools at least a portion of the refrigerant fluid and delivers the portion of the subcooled refrigerant fluid to the pump inlet.

In another aspect combinable with any of the previous aspects, the subcooler includes a subcooler inlet fluidly coupled to the receiver outlet and a subcooler outlet fluidly coupled to the pump inlet.

In another aspect combinable with any of the previous aspects, the flow control device is an ejector having a primary inlet, a secondary inlet, and an outlet. The primary inlet is fluidly coupled to the pump outlet. The system 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 evaporator is fluidly coupled between an outlet of the ejector and the inlet of the liquid separator.

In another aspect combinable with any of the previous aspects, the evaporator is fluidly coupled between the secondary inlet of the ejector and the liquid-side outlet of the liquid separator.

In another aspect combinable with any of the previous aspects, the thermal management system further includes a control valve fluidly coupled between the pump outlet and the primary inlet of the ejector.

In another aspect combinable with any of the previous aspects, the compressor inlet is fluidly coupled to the vapor-side outlet of the liquid separator.

In another aspect combinable with any of the previous aspects, the condenser includes a subcooler. The condenser condenses at least a portion of the refrigerant fluid to a saturated state or a subcooled state. The subcooler subcools at least a portion of the refrigerant fluid and delivers the portion of the subcooled refrigerant fluid to the pump inlet.

In another aspect combinable with any of the previous aspects, the subcooler includes a subcooler inlet fluidly coupled to the receiver outlet and a subcooler outlet fluidly coupled to the pump inlet. In another aspect combinable with any of the previous aspects, the ejector, the liquid separator and the evaporator are a first ejector, a first liquid separator and a first evaporator. The closed-circuit refrigerant system further includes a second ejection, a second liquid separator, and a second evaporator. The second ejector has a primary inlet fluidly coupled to the pump outlet. The second ejector receives the refrigerant fluid from the pump. The second ejector further has a secondary inlet and an outlet. The second liquid separator has an inlet, a vapor-side outlet, and a liquid-side outlet. The second evaporator extracts heat from at least another heat load that is in thermal conductive or convective contact with the second evaporator. The second evaporator is fluidly coupled to the second ejector and the second liquid separator.

In another aspect combinable with any of the previous aspects, the first and second evaporators are fluidly coupled between outlets of the first and second ejectors and inlets of the first and second liquid separators.

In another aspect combinable with any of the previous aspects, the first and second evaporators are fluidly coupled between the respective secondary inlets of the first and second ejectors and the liquid-side outlets of the first and second liquid separators.

Another aspect combinable with any of the previous aspects further includes a compressor bypass circuit. The compressor bypass circuit includes a bypass conduit that fluidly couples the evaporator outlet to the condenser inlet external to the compressor. The control system performs operations including determining that the ambient temperature is less than a lower threshold and based on the determination, turning off the compressor and directing the flow of the refrigerant fluid from the evaporator outlet, through the bypass conduit, and to the condenser inlet.

In another aspect combinable with any of the previous aspects, the compressor bypass circuit further includes a solenoid control valve, a first check valve, and a second check valve. The solenoid control valve is coupled between the vapor-side outlet of the liquid separator and the compressor inlet. The first check valve is coupled to the outlet of the compressor and the second check valve is coupled to the vapor-side outlet of the liquid separator.

In an aspect combinable with the example implementation, the refrigerant fluid is ammonia.

Another aspect combinable with any of the previous aspects further includes an open- circuit refrigeration system that includes the receiver, the evaporator, and the liquid separator. The open-circuit refrigeration system receives the refrigerant fluid from the receiver. In another aspect combinable with any of the previous aspects, the open-circuit refrigeration system further includes a back-pressure regulator having an inlet coupled to the vapor-side outlet of the liquid separator and an exhaust line coupled to the back-pressure regulator. The refrigerant vapor from the exhaust line does not return to the receiver.

In another aspect combinable with any of the previous aspects, the evaporator operates with a vapor quality of less than 1.

In another aspect combinable with any of the previous aspects, the evaporator operates with a value of vapor quality in a range of 0.5 to less than 1 and with the value of the vapor quality avoiding dryout and mist regions of a phase diagram of the refrigerant fluid.

In another aspect combinable with any of the previous aspects, the evaporator operates with a vapor quality of 0.6 to 0.95.

In another aspect combinable with any of the previous aspects, the evaporator operates with a vapor quality of 0.8 to 0.9.

In another aspect combinable with any of the previous aspects, the evaporator operates with a vapor quality of 0.8 to 0.85.

In another aspect combinable with any of the previous aspects, the at least one heat load includes a first heat load and a second heat load. The first heat load is in thermal conductive or convective contact with the evaporator from which heat is removed by the closed-circuit refrigerant system. The second heat load is in thermal conductive or convective contact with the evaporator from which heat is removed by the open-circuit refrigerant system.

In another aspect combinable with any of the previous aspects, the second heat load is a high heat load, relative to the first heat load. The high heat load has one or more characteristics of being at least one of a highly temperature sensitive load or operative for short periods of time, relative to one or more corresponding characteristics of the first heat load.

In another example implementation, a thermal management method includes transporting refrigerant fluid from a receiver through a closed-circuit refrigeration system (CCRS) having a closed-circuit path; pumping, with a pump, the refrigerant fluid from the receiver to a flow control device disposed in the closed-circuit path; controlling, by the flow control device, a thermodynamic property of the refrigerant fluid; extracting heat from at least one heat load that is in thermal conductive or convective contact with an evaporator disposed in the closed-circuit path, with the extracted heat being transferred to the refrigerant fluid having the controlled thermodynamic property to convert at least a portion of the refrigerant fluid into refrigerant vapor; compressing, by a compressor disposed in the closed- circuit path, the refrigerant fluid including the refrigerant vapor received from the evaporator to provide compressed refrigerant fluid including compressed refrigerant vapor; condensing the compressed refrigerant fluid including compressed refrigerant vapor received from the compressor, with a condenser disposed in the closed-circuit path to provide condensed refrigerant fluid; and transporting the condensed compressed refrigerant fluid to the receiver.

An aspect combinable with the example implementation further includes adjusting operation of at least one of the pump or the compressor based on an ambient temperature of a condensing fluid circulated through the condenser to condense the refrigerant fluid.

In an aspect combinable with the example implementation, the flow control device is an expansion valve that has a valve inlet and a valve outlet, with the valve inlet fluidly coupled to a pump outlet of the pump.

In another aspect combinable with any of the previous aspects, the evaporator is fluidly coupled between the valve outlet and a compressor inlet of the compressor.

In another aspect combinable with any of the previous aspects, an evaporator inlet is fluidly coupled to the flow control device outlet, and the method further includes accumulating, with a suction accumulator disposed in the closed-circuit path, refrigerant vapor received from an evaporator outlet of the evaporator and transporting the accumulated vapor to the compressor inlet.

Another aspect combinable with any of the previous aspects further includes bypassing the compressor with a compressor bypass circuit.

In another aspect combinable with any of the previous aspects, the condenser includes a subcooler, and the method further includes condensing, with the condenser, the compressed refrigerant fluid to a saturated state or subcooled state; subcooling the condensed refrigerant fluid with the subcooler; and circulating the subcooled, condensed refrigerant fluid to a pump inlet of the pump.

In an aspect combinable with the example implementation, the flow control device is an ejector having a primary inlet, a secondary inlet, and an outlet and where the primary inlet is coupled to a pump outlet of the pump, and the method further includes separating refrigerant fluid received at an inlet of a liquid separator into refrigerant vapor at a vapor-side outlet of the liquid separator and refrigerant liquid at a liquid-side outlet of the liquid separator. Another aspect combinable with any of the previous aspects further includes mixing refrigerant fluid from the pump with refrigerant fluid received from the liquid-side outlet and circulating the mixed refrigerant fluid to the inlet of the liquid separator.

In another aspect combinable with any of the previous aspects, the refrigerant fluid received from the liquid-side outlet is received at the secondary inlet, and the method further includes transporting the mixed refrigerant fluid to the inlet of the evaporator from the outlet of the ejector.

In another aspect combinable with any of the previous aspects, the refrigerant fluid received from the liquid-side outlet is received at the secondary inlet through the evaporator, and the method further includes transporting the mixed refrigerant fluid to the inlet of the liquid separator.

In another aspect combinable with any of the previous aspects, the condenser includes a subcooler, and the method further includes condensing, with the condenser, the compressed refrigerant fluid to a saturated state or subcooled state, subcooling the condensed refrigerant fluid with the subcooler, and circulating the subcooled refrigerant fluid to the pump inlet.

In another aspect combinable with any of the previous aspects, the ejector, the liquid separator, and the evaporator are a first ejector, a first liquid separator and a first evaporator, and the method further includes transporting the pumped refrigerant fluid through a second ejector having a primary inlet coupled to a pump outlet and a second liquid separator having an inlet, a vapor-side outlet, and a liquid-side outlet and extracting heat from at least another heat load that is in thermal conductive or convective contact with a second evaporator.

Another aspect combinable with any of the previous aspects further includes turning off the compressor during operation at a low ambient temperature.

Another aspect combinable with any of the previous aspects further includes by passing the compressor during operation at the low ambient temperature.

In another aspect combinable with any of the previous aspects, by -passing includes closing a solenoid control valve coupled between the vapor-side outlet of the liquid separator and a compressor inlet to divert refrigerant vapor from the vapor-side outlet through first and second check valves. The first check valve is coupled to the outlet of the compressor and the second check valve is coupled to the vapor-side outlet of the liquid separator.

Another aspect combinable with any of the previous aspects further includes discharging the refrigerant vapor through an exhaust line so that the discharged refrigerant vapor is not returned to the receiver. Another aspect combinable with any of the previous aspects further includes transporting the refrigerant fluid from the receiver through an open-circuit refrigeration system that includes an open-circuit refrigeration fluid path including the receiver, the ejector, the evaporator, and the liquid separator, and to an exhaust line.

Another aspect combinable with any of the previous aspects further includes discharging refrigerant vapor through a back-pressure regulator having an inlet coupled to the vapor-side outlet of the liquid separator and into an exhaust line with the discharged refrigerant vapor not returning to the receiver.

In another aspect combinable with any of the previous aspects, the evaporator operates with a value of vapor quality of less than 1, and with the value of the vapor quality avoiding dryout and mist regions of a phase diagram of the refrigerant fluid.

In another aspect combinable with any of the previous aspects, the evaporator operates with a vapor quality of in a range of 0.5 to less than 1.

In another aspect combinable with any of the previous aspects, the evaporator operates with a vapor quality of 0.6 to 0.95.

In another aspect combinable with any of the previous aspects, the evaporator operates with a vapor quality of 0.8 to 0.9.

In another aspect combinable with any of the previous aspects, the evaporator operates with a vapor quality of 0.8 to 0.85.

Another aspect combinable with any of the previous aspects further includes removing heat from a first heat load of the at least one heat load that is in thermal conductive or convective contact with the evaporator and removing heat from a second heat load of the at least one heat load that is in thermal conductive or convective contact with the evaporator.

In another aspect combinable with any of the previous aspects, the second heat load is a high heat load, relative to the first heat load. The high heat load has one or more characteristics of being at least one of a highly temperature sensitive load or operative for short periods of time, relative to one or more corresponding characteristics of the first heat load.

In an aspect combinable with the example implementation, the refrigerant fluid is ammonia.

One or more of the above aspects may include one or more of the following advantages/operational features.

By including a pump that pumps liquid through the heat source, at low or very low ambient temperatures the liquid evaporates in the heat source and is condensed in the heat sink at virtually the same pressure or at slightly higher pressure to overcome pressure drops in the lines and components between the condenser and evaporator path. No compressor is needed at low or very low ambient temperature. The pump’s dimensions, weight, and power however are significantly smaller than those of the compressor. Thus, by adding the pump downstream from the condenser and the liquid refrigerant receiver, at low or very low ambient temperature, the compressor can be turned off to save power, while the pump, using less power, pumps the liquid refrigerant through the flow control device, the evaporator, and the condenser. Alternatively, it can bypass the expansion valve or the expansion valve can stay fully open to reduce pressure drop which the pump should overcome. The flow control device (as an expansion valve) and the pump at a set pump speed turns the liquid into a two- phase liquid/vapor mixture. The liquid portion is evaporated in the evaporator during cooling of heat load(s). The flow control device maintains a set superheat at the evaporator outlet, while superheated vapor is pushed through the compressor, which is off, and enters the condenser where the refrigerant is condensed extracting heat from the system, and the condensed refrigerant is returned to receiver. Alternatively, the flow control device may maintain a vapor quality at the evaporator exit provided that the refrigerant stream exiting the evaporator bypasses the compressor, which is off, and enters the condenser.

Use of an ejector can improve performance of the refrigeration system. When the refrigeration system employs an ejector, a liquid separator, and an evaporator, the ejector operates as a booster-compressor, reducing power used by the compressor or used as an overfeeding device. The ejector can control operation of evaporator in two-phase region which is needed for cooling high heat loads. When ejector is used, the evaporator exit state is a liquid-vapor two-phase state.

Ejector performance is characterized by a pressure lift, an entrainment ratio, a motive pressure, and a motive mass flow rate. In order to enable recirculation of the refrigerant flow from the secondary inlet at a suitable rate, the pressure lift should exceed the pressure of the evaporator between the ejector outlet and the ejector secondary inlet. The mass flow rate through the evaporator is the sum of the motive mass flow rate and the secondary (recirculation) mass flow rate. The secondary to motive mass flow rate ratio is the entrainment ratio.

At low ambient temperature the condensation and the compressor discharge pressure reduces creating a thermodynamic advantage for the cycle. An additional advantage of the added pump is to boost the pressure at the ejector nozzle inlet when the compressor discharge pressure is not sufficient to entrain liquid refrigerant via the secondary inlet. This may work when the compressor is ON or OFF.

Some aspects enable placing the compressor in an off state, and cooling heat loads while ambient is at low temperatures. The pump circulates refrigerant liquid through the flow control device, which may or may not convert refrigerant liquid into a mixed refrigerant liquid/vapor (e.g., depending on the states of the compressor and pump). The liquid portion is evaporated in the evaporator during cooling of heat load(s). The flow control device maintains a set superheat at the evaporator outlet, while superheated vapor is pushed through the compressor, which is off, and enters the condenser where the refrigerant is condensed extracting heat from the system, and the condensed refrigerant is returned to receiver. Alternatively, the flow control device may maintain a vapor quality at the evaporator exit provided that the refrigerant stream exiting the evaporator bypasses the compressor, which is off, and enters the condenser.

The thermal management system described herein includes a closed-circuit refrigeration system that includes a 1) a pump to operate a low ambient temperature with no compressor, and/or 2) pump and ejector which decouple compressor and ejector performance and enable desirable motive pressure (pressure at the ejector inlet), pressure lift, and entrainment ratio, while also providing the capability to intentionally design a high pressure drop evaporator, minimizing refrigerant distribution issues.

Some embodiments of the thermal management system described herein are a closed- circuit refrigeration system integrated with an open-circuit refrigeration system. The presence of the open-circuit refrigeration system allows the thermal management system to maintain a temperature of a load within a relatively small tolerance of a temperature set point.

Directed energy systems that are mounted to mobile vehicles, such as trucks, or that exist in space may be ideal candidates for cooling by the thermal management system presented, as such systems may include high heat load, 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 thermal loads, are particularly well suited for operation with such directed energy systems.

The disclosed thermal management system (TMS) may be specified to cool two different kinds of heat loads - high heat loads (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). The TMS avoids the need for 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).

The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1-3 are schematic diagrams of examples of a thermal management system that includes a pump and a flow control device, with the pump enhancing a performance of the flow control device.

FIGS. 4-7 are schematic diagrams showing alternative configurations for arrangement of evaporators/loads on the integrated open-circuit/closed-circuit refrigeration system, generally applicable to described embodiments.

FIG. 8 is a block diagram of a control system.

FIG. 9 is a schematic diagram of an example of a thermal management system that includes a power generation apparatus.

FIG. 10 is a schematic diagram of an example of directed energy system that includes a thermal management system.

DETATEED DESCRIPTION

A refrigeration system pumps heat from a heat source to a heat sink when the heat source temperature is substantially lower than heat sink temperature. Vapor compression refrigeration systems are configured to interact between the heat sink and the heat source. A compressor is needed to enable that interaction. The compressor compresses refrigerant vapor to a pressure which corresponds to a condensation temperature that is higher than the heat sink temperature. The heat of condensation is transferred to the heat sink due to the temperature difference between the condensation temperature and the heat sink temperature. This causes condensation of vapor refrigerant. The high pressure liquid refrigerant is expanded to a low pressure which corresponds to an evaporation temperature lower than the heat source temperature. At the low pressure, the liquid refrigerant turns into a mixture of liquid and vapor. The heat from the heat source is transferred to the liquid portion of mixture due to the temperature difference between the heat source temperature and evaporation temperature causing complete evaporation of the liquid port. In aerospace applications, the temperature of air outside the vehicle (heat sink) may become very low with respect to the heat source temperature. In this case, the condensation temperature (and the pressure which corresponds to the condensation temperature), can be lightly higher, about the same, or even lower than the evaporation temperature (or the pressure corresponding to the evaporation temperature).

Embodiments described in the present disclosure include a CCRS that includes a pump to enable operation at low ambient temperature with a flow control device, (which can be an expansion valve or ejector). When a compressor is not used, the compressor power is saved. If an ejector is used, when the compressor discharge pressure is low at low ambient temperature, the pump creates sufficiently high pressure for ejector motive nozzle, and the compressor operates at low pressure ratio saving power if the pressure ratio is within the operating range of the compressor. If the pressure ratio is below the compressor operating range, the compressor is OFF and the pump is ON.

Often TMS for directed energy applications deal with large heat loads acting for short periods and small heat loads operating continuously. In some aspects, embodiments of the present disclosure can combine a closed-circuit refrigeration system (CCRS) with an open- circuit refrigeration system (OCRS). A CCRS can cover small heat loads operating continuously. An OCRS can cover large heat loads acting for short periods. Cooling of large loads and high heat loads that are also highly temperature sensitive can present a number of challenges. On the one hand, such loads generate significant quantities of heat that is extracted during cooling. In conventional CCRSs, cooling high heat loads typically involves circulating refrigerant fluid at a relatively high mass flow rate. However, CCRS 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 typically heavy and consume significant power. As a result, many CCRSs 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.

In some cases, a thermal management system (TMS) may be specified to cool two different kinds of heat loads - high heat loads (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 thermal 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.

Such systems may not be acceptable for mobile and space applications. Also, start-up and/or transient processes may exceed the short period in which cooling duty is applied for the high heat loads that are operative for short periods of time. Transient operation of such systems cannot provide precise temperature control. Therefore, thermal energy storage (TES) units are integrated with small refrigeration systems and recharging of such TES units are used instead. Still TES units may be too heavy and too large for mobile and space applications. In addition, such systems are complex devices and reliability may present problems especially for critical applications.

In particular, the thermal management systems and methods disclosed herein include a number of features that reduce both overall size and weight relative to conventional refrigeration systems, and still extract excess heat energy from both high heat load, highly temperature sensitive components and relatively temperature insensitive components, to accurately match temperature set points for the components.

At the same time, the disclosed thermal management systems that use the compressor would, in general, require less power than conventional closed-circuity systems for a given amount of refrigeration over a specified period(s) of operation. Whereas certain conventional refrigeration systems used closed-circuit refrigerant flow paths, the systems and methods disclosed herein use modified closed-circuit refrigerant flow paths, and in some implementations, use closed-circuit refrigerant flow paths in combination with open-cycle refrigerant flow paths to handle a variety of heat loads. Depending upon the nature of the refrigerant fluid, exhaust refrigerant fluid from open-circuit refrigerant flow paths may be incinerated as fuel, chemically treated, and/or simply discharged at the end of the flow path.

Refrigeration systems that cool the heat loads at low ambient temperature employ head pressure controls to enable effective operation of compression and expansion devices. When ambient temperature is reduced, the head pressure control maintains a minimal discharge pressure to provide adequate pressure differential across a flow control device. The compressor power consumption improves when ambient temperature is reduced, but does not allow a full benefit from low ambient temperature conditions. Discussed below are embodiments of refrigeration systems for use in a thermal management system (TMS) that effectively cools the heat loads at low ambient temperature at the same time has reduced power consumption at low ambient temperature. 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 thermal loads, are particularly well suited for operation with such directed energy systems.

Referring to FIG. 1, an example of a thermal management system (TMS) 100 that includes a closed-circuit refrigerant system (CCRS) 102 is shown. The CCRS 102 can include a closed flow path for a refrigerant fluid to provide closed-circuit refrigeration for, in some examples, low ambient operation and, in some cases, low heat loads over long time intervals (and in some cases, both low and high heat loads over long and short periods of time, respectively).

More specifically, the CCRS 102 includes a receiver 110 that includes an inlet 109 and an outlet 111. The receiver 110 is configured to store liquid refrigerant, for example, a subcooled liquid refrigerant. The outlet 111 is coupled to an inlet 113 of a pump 112 and an outlet 115 of the pump 112 is coupled to an inlet of a solenoid control valve 124 (optional). An outlet of the solenoid control valve 124 is coupled to an inlet 117 of a flow control device 114. In this example, the flow control device 114 can be an expansion device, i.e., an expansion valve or orifice having an outlet 119 coupled an inlet 121 of an evaporator 116. (The evaporator 116 can take on various configurations with detailed examples shown in FIGS. 4-7).

Receiver 110 can also 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 the pressure relief 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 (not shown) applied around the receiver 110 to reduce thermal losses.

In general, receiver 110 can have a variety of different shapes. In some embodiments, for example, the receiver 110 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 within receiver 110 is discharged first through outlet 111, prior to discharge of refrigerant vapor. 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.

The evaporator 116 has an outlet 123 that is coupled to an inlet 125 of an optional suction accumulator 122. The suction accumulator 122 accumulates vapor that is outputted from a vapor-side outlet 127 coupled to an inlet 101 of a compressor 104. When the optional suction accumulator 122 is not used, the outlet of the flow control device 114 is coupled to the inlet 101 of the compressor 104. The compressor 104 has a compressor outlet 103 coupled to a condenser inlet 105 of a condenser 106. The condenser 106, in some aspects, is an air-cooled condenser. The condenser 106 includes a fan 108 (e.g., fixed, two-speed, or variable speed) in proximity to the condenser 106 to move a condensing fluid 126, such as an airflow, across the condenser 106. The condenser 106 has a condenser outlet 107 coupled to the inlet 109.

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).

In general, the solenoid control valve 124 includes a solenoid that uses an electric current to generate a magnetic field to control a mechanism that regulates an opening in a valve to control fluid flow. The solenoid control valve 124 is configurable to stop refrigerant flow as an on/off valve, if the pump 112 cannot shut off refrigerant flow robustly.

The CCRS 102 provides cooling for low heat loads 118 over long time intervals and may provide cooling for high heat loads 120 over short time intervals. The heat loads may be highly temperature sensitive heat loads, i.e., sensitive to relatively small changes in temperature.

In this example implementation, the CCRS 102 includes a control system 999 (see FIG. 8 for an exemplary embodiment) that produces control signals (based on sensed thermodynamic properties) to control operations of one or more of the pump 112, the flow control device 114, the solenoid control valve 124, the compressor 104, and/or the fan 108, as needed. Control system 999 may receive signals, process received signals and send signals (as appropriate) from/to the solenoid control valve 124, and from/to a motor of the pump 112 and a motor of the compressor 104 or fan 108 changing their speeds, shutting the pump 112 or compressor 104 off or starting them, etc.

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.

The TMS 100 includes a low heat load 118 that is coupled to, and/or in thermal conductive or convective communication with, the evaporator 116. The evaporator 116 is configured to extract heat from the low heat load 118. In some aspects, the evaporator 116 can refrigerant fluid channels and that includes a thermal load. The evaporator 116 can be implemented in a variety of ways. In general, evaporator 116 functions as a heat exchanger, providing thermal contact between the refrigerant fluid and heat loads 118, 120. Typically, evaporator 116 includes one or more refrigerant fluid channels extending internally between an inlet 121 and an outlet 123 of the evaporator 116, allowing refrigerant fluid to flow through the evaporator 116 and absorb heat from heat loads 118, 120.

A variety of different evaporators can be used in TMS 100-300. In general, any cold plate may function as the evaporator 116 of the open-circuit refrigeration systems disclosed herein. Evaporator 116 can accommodate any 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 refrigerant fluid channels, can be attached to the heat loads 118, 120 mechanically, or can be welded, brazed, or bonded to the heat load in any manner. In some embodiments, evaporator 116 (or certain components thereof) can be fabricated as part of heat loads 118, 120 or otherwise integrated into one or more of the heat loads 118, 120, in which heat load 120 has one or more integrated, refrigerant fluid channels. The portion of high heat load 120 with the refrigerant fluid channels 902 effectively functions as the evaporator 116. The evaporator 116 can be implemented as multiple evaporators 116 connected in parallel and/or in series or as individual evaporators 116, as shown for evaporator 116 for high heat load 120 (see FIGS. 4-7 for possible implementations).

The TMS 100, in some aspects, can be operated based at least in part on a temperature of a condensing fluid, such as the condensing fluid 126. In some aspects, the condensing fluid 126 is an ambient airflow at a particular ambient temperature. When the ambient temperature is high, the pump 112 can be turned OFF. On the other hand, when the ambient temperature is very low, compared to when the ambient temperature is high, the compressor 104 is OFF and the pump 112 is ON.

Generally, the TMS 100 (as well as TMS 200 and 300) operate between high (also called compressor discharge, condensation, or head) pressure (labeled PD in FIGS. 1-3) and low (also called evaporation or compressor suction) pressure (labeled Ps in FIGS. 1-3). A compressor compresses refrigerant from the suction (low) to the discharge (high) pressure. A flow control device, such as an expansion valve, expands refrigerant from the high pressure to the low pressure. This refers to pressure difference DP = PD - Ps. High and low ambient temperature impacts pressures in the TMS 100 (and 200 and 300). High and low ambient temperatures are defined by and relative to the operating pressure differences found in the components of the TMS 100 (and 200 and 300). The higher the ambient temperature, the higher the compressor discharge pressure (PD) and pressure differential (DP). Similarly, the lower the ambient temperature, the lower the compressor discharge pressure (PD) and the lower the pressure differential (DP). Ambient temperature can be sufficiently low that PD and DP fall outside of the operating range of an expansion device and/or a compressor. An expansion device (or an ejector) may not work well when pressure difference is below design levels. Each compressor, expansion device, and ejector can have a design high limit and low limit for pressure.

The pump 112 pumps liquid refrigerant through the flow control device 114, in which high pressure liquid turns into a two-phase liquid/vapor mixture in the flow control device 114. The liquid portion evaporates in the evaporator 116 during cooling of the low heat load 118. The flow control device 114 maintains a set superheat at the outlet 123 of the evaporator 116 producing superheated vapor. The superheated vapor is pushed through the compressor 104 and enters the condenser 106. In the condenser 106, the refrigerant is condensed and enters the receiver 110, and the cycle is repeated.

Under some ambient conditions, both the compressor 104 and the pump 112 are ON. The compressor 104 compresses refrigerant vapor to a pressure that corresponds to a saturated temperature sufficiently higher than ambient temperature. The compressed refrigerant is condensed in the condenser 106. At the outlet 111 of the receiver 110, the pump 112 elevates the refrigerant pressure and adjusts for a proper pressure differential across the flow control device 114. The high pressure refrigerant liquid is turned into the two-phase mixture in the flow control device 114. The liquid portion evaporates in the evaporator 116, during cooling of the low heat load 118. The flow control device 114 maintains a set superheat at the outlet 123 of the evaporator 116. The superheated vapor is pushed through the compressor 104 and enters the condenser 106. In the condenser 106 the refrigerant is condensed into a liquid and enters the receiver 110 to repeat the cycle.

The CCRS 102 (as well as CCRS 202 and CCRS 302 discussed below) can use the pump 112 to reduce both overall size and weight relative to a conventional refrigeration system sized for the expected heat load(s), while extracting excess heat energy from low heat loads and in some embodiments high heat loads.

Referring to FIG. 2, an example of a thermal management system (TMS) 200 that includes a closed-circuit refrigerant system (CCRS) 202 is shown. As compared to TMS 100 and CCRS 102, the CCRS 202 can optionally include a compressor bypass circuit 204. The CCRS 202 can also optionally include a pump bypass circuit 220. The CCRS 202 can also optionally include a subcooling circuit 212. Thus, example implementations of the CCRS 202 can include one, some, or all of the optional compressor bypass circuit 204, pump bypass circuit 220, and subcooling circuit 212. Other features of FIG. 2 are discussed with reference to FIG. 1.

An alternative arrangement of a CCRS 202 that enables bypassing refrigerant fluid through the compressor 104 is shown through the implementation of the compressor bypass circuit 204, with the compressor 104 OFF to avoid a pressure drop produced by the compressor 104 when off. The CCRS 202 bypasses the compressor 104 by routing refrigerant through a bypass conduit 206 of the compressor bypass circuit 204, as well as by through a pair of check valves 210 and an optional solenoid control valve 208. Some embodiments may include a suction accumulator 122 at the outlet 123 of the evaporator 116.

Another alternative arrangement of the CCRS 202 that enables bypassing refrigerant fluid through the compressor 104 through the implementation of the compressor bypass circuit 204 and the pump bypass circuit 220, with the compressor 104 OFF or when the pump 112 is OFF is illustrated. To avoid pressure drops produced by non-operating components (i.e., compressor 104 and/or pump 112). This arrangement bypasses the compressor 104, via the check valves 210 and an optional solenoid control valve 208. The arrangement also bypasses the pump 112 and the solenoid control valve 124 through a bypass conduit 222 and a check valve 224. Some embodiments may include a suction accumulator 122 at the outlet 123 of the evaporator 116. Pump operation can be sensitive to cavitation and thus requires liquid refrigerant at the inlet 113 of the pump 112. Refrigerant vapor should be avoided at the inlet 113 of the pump 112.

Another alternative arrangement of CCRS 200 has the optional subcooling circuit 212. Refrigerant vapor is compressed in the compressor 104 and is condensed in the condenser 106. In the condenser 106, the refrigerant vapor condenses to a saturated state or slightly subcooled state and enters the receiver 110. The refrigerant from the receiver 110 enters a subcooler inlet of a subcooler 214 of the condenser 106 from an input conduit 218 that is provided for subcooling of the refrigerant from the receiver 110. The subcooled refrigerant is fed from a subcooler outlet 213, through an output conduit 216 to the pump 112 that pumps the subcooled liquid into the flow control device 114 (or the evaporator 116, if the flow control device 114 is not used). The optional subcooling circuit 212 can be used in combination with one or both of the optional compressor bypass circuit 204 and the pump bypass circuit 220 (or without either of the optional compressor bypass circuit 204 and the pump bypass circuit 220).

Referring to FIG. 3, an example of a thermal management system (TMS) 300 that includes a closed-circuit refrigerant system (CCRS) 302 is shown. The pump 112 may be helpful in various architectures that include ejectors as described below in reference to TMS 300. The pump 112 operates as a booster device maintaining a needed pressure differential across a motive nozzle of the ejector when ambient temperature drives the discharge pressure below a certain point. Referring to FIG. 3, the example of the CCRS 302 is configured as an ejector-pump boost (EPB) closed-circuit system (EPB-CCRS 302). TMS 300 can provide closed-circuit refrigeration for low heat loads over long time intervals.

The EPB-CCRS 302 includes the receiver 110 that includes the inlet 109 and the outlet 111. The outlet 111 is coupled to the inlet 113 of the pump 112 and the outlet 115 of the pump 112 is coupled to the solenoid control valve 124. The solenoid control valve 124 is then coupled to a motive inlet 307 of an ejector 310 and an outlet 311 of the ejector 310 is coupled the inlet 121 of the evaporator 116. The evaporator 116 can take on various configurations with detailed examples shown in FIGS. 4-7.

The evaporator 116 has the outlet 123 that is coupled to an inlet 301 of a liquid separator 330 that includes a vapor section 304 and a liquid section 306. The liquid separator 330 further has a liquid-side outlet 305 coupled to a suction inlet 309 of the ejector 310 and a vapor-side outlet 303 coupled to the inlet 101 of the compressor 104.

In some aspects, liquid separator 330 can be implemented as a coalescing liquid separator or a flash drum, for example, which has the vapor-side outlet 303 and the inlet 301 coupled to conduits (not referenced) and has a liquid-side outlet 305. Other conventional details such as membranes, coalescing filters, or meshes (not shown) can be included in the liquid separator 330.

The compressor 104 has the compressor outlet 103 coupled to the condenser inlet 105 of the condenser 106. The condenser 106 is usually an air-cooled condenser. The condenser 106 includes the fan 108 in proximity to the condenser 106. The condenser 106 has the condenser outlet 107 coupled to the inlet 109. The EPB-CCRS 302 provides cooling for low heat loads 118 over long time intervals and may provide cooling for high heat loads 120 over short time intervals. The receiver 110 is configured to store subcooled liquid refrigerant.

EPB-CCRS 302 also includes the control system 999 (see FIG. 8 for an exemplary embodiment) that produces control signals (based on sensed thermodynamic properties) to control operation of the pump 112, the solenoid control valve 124, and the compressor 104, as needed. Control system 999 may receive signals, process received signals and send signals (as appropriate) from/to the solenoid control valve 124, and from/to the motor of the pump 112 and the motor of the compressor 104 changing their speeds, shutting the pump 112 or compressor 104 off or starting them, etc.

The TMS 300 includes the low heat load 118 that is coupled to, and/or in thermal communication with, the evaporator 116. The evaporator 116 is configured to extract heat from the low heat load 118.

The presence of the pump 112 in TMS 300 can decouple compressor and ejector performance and enables a desirable motive pressure (pressure at the motive inlet 307), a desirable pressure lift, and a desirable entrainment ratio, while also providing the capability to use a high pressure drop evaporator with minimal refrigerant distribution issues. The pump 112 is configured to elevate the pressure above the condensation pressure and a head pressure control mechanism is configured to regulate pressure differential across the ejector 310. As compared to TMS 100 and CCRS 102, the EPB-CCRS 302 can optionally include a compressor bypass circuit 204. The EPB-CCRS 302 can also optionally include a pump bypass circuit 220. The EPB-CCRS 302 can also optionally include a subcooling circuit 212. Thus, example implementations of the EPB-CCRS 302 can include one, some, or all of the optional compressor bypass circuit 204, pump bypass circuit 220, and subcooling circuit 212.

The TMS 300 can integrate the following control strategies. The compressor discharge pressure is dictated by the ambient temperature. The condensing temperature, that is the saturated temperature at the compressor discharge pressure, is always higher than the ambient temperature. At the same time, the compressor 104 is capable of generating a discharge pressure within a given range, i.e., the compressor 104 cannot operate below a certain discharge pressure limit. At the same time, the ejector performance restricts a range of the pressure differential across the motive nozzle. That is, the ejector 310 cannot operate below a pressure differential limit.

If the ambient conditions reduce the discharge/condensation pressure below the discharge pressure limit and/or the pressure differential across the motive nozzle is below the pressure differential limit, a head pressure control mechanism is engaged. Approaches to control head pressure involve the condenser 106 coupled with the fan 108 in the condenser 106 that are configured to operate as the head pressure control mechanism.

Normally, the variable speed fan 108 (as a multi- or variable speed fan) operates at a full speed. When the ambient temperature is reduced, the discharge pressure is concomitantly reduced, providing performance benefits for the system (such as higher cooling capacity). When one of the limits is hit, the head pressure control mechanism is engaged, reducing the condenser fan speed in order to keep the compressor discharge and condensation pressures sufficiently high. Other conventional head pressure controls can be used as well. The head pressure control mechanism regulates the pressure differential across the ejector 310 which enables proper ejector pressure lift and the related entrainment ratio. If the motive pressure (the pressure at the outlet 311) exceeds the discharge pressure, the pump 112 is engaged. When the pump 112 is OFF, the liquid refrigerant is pushed through the pump 112 causing just a pressure drop. Alternatively, the pump 112 can be bypassed (with optional pump bypass circuit as shown in FIG. 3 to avoid the pressure drop in the pump 112, when not in operation.

Sensors that measure head pressure (e.g., sensor Pd, the pressure on the compressor discharge side) and the pressure differential across the ejector 310 (e.g., sensor Peout and Pein) are used to enable the control strategies discussed above. When the low heat load 118 is applied, the TMS 300 is configured to have the EPB- CCRS 302 provide refrigeration to the low heat load 118.

In the closed-circuit refrigeration system, 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). The compressor 104 performance generally restricts the compressor discharge pressure range. The compressor 104 cannot operate below a certain discharge pressure. The superheated vapor is at a temperature and pressure at which it can be condensed in the condenser 106 generally by cooling air flowing across a coil or tubes in the condenser 106. The condenser 106 coupled with the fan 108 are configured to operate as the above-mentioned head pressure control mechanism. At the condenser 106, the circulating refrigerant loses heat and thus removes heat from the TMS 300, which removed heat is carried away by either the water or air (whichever may be the case) flowing over the coil or tubes, providing a condensed liquid refrigerant.

The condensed and subcooled liquid refrigerant is routed into the receiver 110, exits the receiver 110, and enters the pump 112. The pump 112 pumps the liquid refrigerant through the solenoid control valve 124 (if used) and into the ejector 310, where the refrigerant is enthalpically expanded and the pumped subcooled liquid refrigerant turns into a liquid-vapor mixture at a low pressure and temperature. At the same time, the ejector performance restricts the range of the pressure differential across the motive nozzle. If the ambient conditions reduce the discharge/condensation pressure below the limit and/or the pressure differential across the motive nozzle is below the limit, the head pressure control mechanism is engaged. The temperature of the liquid and vapor refrigerant mixture (evaporating temperature) is lower than the temperature of the low heat load 118. The mixture is routed through a coil or tubes in the evaporator 116.

The ejector 310 acts as a pump to move a secondary fluid flow, e.g., liquid in the liquid section 306 from the liquid-side outlet 305 of the liquid separator 330 using energy of the primary refrigerant flow from the receiver 110, via the pump 112. In some aspects, the ejector 310 includes a high-pressure, primary inlet (e.g., motive inlet 307) coupled to a motive nozzle, a suction (e.g., suction inlet 309), one or more secondary nozzles that feeds a suction chamber, a mixing chamber for a primary flow of refrigerant and secondary flow of refrigerant to mix, and a diffuser section located at and outlet (e.g., outlet 311). In example embodiments, the ejector 310 is passively controlled by built-in flow control.

Liquid refrigerant from the receiver 110 is pumped by the pump 112 providing the primary flow. In the motive nozzle, potential energy of the primary flow from motive inlet 307 is converted into kinetic energy reducing the potential energy (the established static pressure) of the primary flow. The secondary flow from the liquid-side outlet 305 of the liquid separator 330 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 309 and the secondary nozzle(s) internal to the ejector 310. The two streams (primary flow and secondary flow) can mix together in the mixing chamber. In the diffuser section, the kinetic energy of the mixed flows is converted into potential energy elevating the pressure of the mixed flow liquid/vapor refrigerant that leaves the ejector 310 at the outlet 311.

In the context of open-circuit refrigeration systems, the use of the ejector 310 allows for recirculation of liquid refrigerant captured by the liquid separator 330 to increase the efficiency of the TMS 300. That is, by allowing for some recirculation of refrigerant, while minimizing the need for a compressor 104 and a condenser 106, this recirculation reduces the required amount of refrigerant needed for a given amount of cooling of high heat loads 120 over a given period of operation.

The heat from the heat load 118, in contact with or proximate to the evaporator 116, 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 liquid separator 330. The saturated or superheated vapor exits the vapor section 304 of the liquid separator 330 and enters the compressor 104. The evaporator 116 is where the circulating refrigerant absorbs and removes heat from the applied low heat load 118, which heat is subsequently rejected in the condenser 106 and transferred to an ambient by water or air used in the condenser 106. To complete the refrigeration cycle, the refrigerant vapor from the evaporator 116 is stored in the liquid separator 330 and again a saturated vapor portion of the refrigerant in the liquid separator 330 is routed back into the compressor 104.

The EPB-CCRS 302 uses the pump 112 to reduce both overall size and weight relative to a conventional refrigeration system sized for the expected heat load(s), while extracting excess heat energy from both low heat loads and high heat loads.

Referring again to FIG. 3, the TMS 300 includes an alternative EPB-CCRS 302 with the evaporator 116 attached at the suction side of the ejector, i.e., between the liquid-side outlet 305 of the liquid separator 330 and the suction inlet 309 of the ejector 310, as shown with the dashed line box labeled 302. Thus, in an example implementation of TMS 300 and EPB-CCRS 302 can have the evaporator 116 (with associated heat loads 118 and/or 120) between the liquid-side outlet 305 of the liquid separator 330 and the suction inlet 309 of the ejector 310 rather than between the outlet 311 of the ejector 310 and the inlet 301 of the liquid separator 330. An advantage of this arrangement is the presence of an elevated, saturated suction temperature with respect to the evaporating temperature. In this arrangement, the ejector 310 should “pump” the refrigerant liquid at a higher vapor quality compared with the arrangement in which the evaporator 116 is between the outlet 311 of the ejector 310 and the inlet 301 of the liquid separator 330. This may result in higher pressure differential across the ejector 310 and more often pump engagement. However, the pumping power is still negligible compared with the compressor power.

When operating in a closed circuit refrigeration configuration, and when the low heat load 118 is applied, the TMS 300 is configured to have the EPB-CCRS 302 provide refrigeration to the low heat load 118. The closed-circuit refrigeration operation is similar but for the positioning of the evaporator 116. The heat from the heat load 118, in contact with or proximate to the evaporator 116, partially or completely evaporates the liquid portion of the two-phase refrigerant mixture, and may superheat the mixture. In FIG. 3 with the alternative placing of the evaporator 116, the refrigerant leaves the liquid-side outlet 305 of the liquid separator 330 and enters the evaporator 116. The refrigerant liquid/vapor mixture leaves the evaporator 116 and enters the suction inlet 309 of the ejector 310. The ejector 310 acts as a “pump,” to “pump” the secondary fluid flow, e.g., the refrigerant vapor/liquid from the outlet of the evaporator 116, using energy of the primary refrigerant flow from the receiver 110 that is pumped via the pump 112.

If the ambient conditions reduce the discharge/condensation pressure below the limit and/or the pressure differential across the motive nozzle is below the limit, the head pressure control mechanism, as discussed above, is engaged. Using the energy of the primary refrigerant flow from the receiver 110, via the pump 112, the refrigerant is channeled into the inlet 301 of the liquid separator 330. The evaporator 116 is where the circulating refrigerant absorbs and removes heat from the applied low heat load 118, which heat is subsequently rejected in the condenser 106 and transferred to the ambient by water or air used in the condenser 106.

Referring still to FIG. 3, TMS 300 can include an alternative arrangement that reduces the risk of pump cavitation as may be present in the embodiments of FIG. 1 through the subcooling circuit 212. The condenser 106 can provide subcooling through the entire operating range. One way to minimize pump cavitation is to increase the liquid subcooling.

Accordingly, heat rejection can be executed in two steps: first, in the condenser 106 and then in the subcooler 214 (e.g., an internal or external heat exchanger, for example). In the condenser 106 the refrigerant condenses and maintains a zero or near zero subcooling. Then, the condensed refrigerant, which may or may not contain some amount vapor, is transported to the receiver 110. Liquid from the receiver 110 is directed to subcooler 214 that provides a set amount of subcooling to the refrigerant (i.e., reduce the refrigerant temperature by a given number of degrees below the refrigerant condensing temperature). P _e -m is the motive inlet 307 pressure of the ejector 310 and P _e -out is the ejector outlet 311 pressure. Pd is the compressor 104 discharge pressure at the compressor outlet 103.

When operating in a closed circuit refrigeration configuration with the optional subcooling circuit 212, when the low heat load 118 is applied, the TMS 300 is configured to provide refrigeration to the low heat load 118. The condenser 106 provides subcooling through the entire operating range of operation. The condenser 106 condenses the refrigerant and maintains a zero or near zero subcooling. Then, the condensed refrigerant, which may or may not contain some amount vapor, is transported to the receiver 110. Liquid from the receiver 110 is directed to the subcooler 214 that provides a set value of subcooling to the refrigerant. If the ambient conditions reduce the discharge/condensation pressure below the limit and/or the pressure differential across the motive nozzle is below the limit, the head pressure control mechanism, as discussed above, is engaged.

The TMS 300 can include an alternative arrangement (not shown) with multiple evaporators 116 and multiple ejectors 310. For example, the solenoid control valve 124 (optional) as well as the components shown in the dashed line box of FIG. 3 of: the ejector 310, evaporator 116, and liquid separator 330 can be duplicated (or increased threefold, or so on). The outlet 115 of the pump 112 provides refrigerant liquid to the solenoid control valve 124 and, in some aspects, a second solenoid control valve. The motive inlets 307 of the multiple ejectors 310 can be attached to solenoid control valves 124. Outlets 311 of the multiple ejectors 310, respectively, are coupled to inlets 121 of the multiple evaporators 116. Outlets 123 of the multiple evaporators 116 are coupled to the inlet 301 of the liquid separator 330 and another inlet 301 of a second liquid separator 330, respectively. Vapor- side outlets 303 feed vapor to a junction which combines the feeds and delivers the vapor to the inlet 101.

In such an embodiment with multiple ejector 310, evaporator 116, and liquid separator 330 with a combination of one of each arranged in a “section,” each section has its own solenoid control valve 124, ejector 310, evaporator 116, and liquid separator 330.

Control system 999 senses a suction pressure differential between ejectors 310 and the compressor 104, and generates signals for the solenoid control valves 124. Alternatively, control system 999 can sense a suction pressure differential between each of the ejectors 310 and the compressor 104, and generate signals for each solenoid control valve 124 to control each evaporator 116 individually, provided that each of the ejectors 310 is equipped with its own pressure differential sensor to deal with differences built-in cold plates of the evaporators 116.

One pump 112 can be used for all sections; however, individual pumps 112 can be used for each section as well. A common solenoid control valve 124, or a common ejector 310, or a common liquid separator 330 may be used as well. The TMS 300 may contain one or more evaporators 116 loaded differently. In this case each section (or some sections) may have its own pump 112 to enable control based on pressure differential across the related ejector 310. When operating in a closed circuit refrigeration configuration, and when the low heat loads 118 are applied, the TMS 300 is configured to provide refrigeration to the low heat loads 118. Each section will operate generally according to FIG. 3, including the head pressure control mechanism, as discussed above.

In some cases, with any of the embodiments, when ambient temperature is low, the needed cooling can be reached by only using the pump 112, and keeping the compressor 104 OFF through the optional compressor bypass circuit 204. The pump 112 pumps liquid refrigerant through the evaporator 116. The resulting vapor pushes the suction of refrigerant vapor and discharge valves of the compressor 104 open, allowing the vapor to circulate through the compressor 104 and reach the condenser 106. The vapor condenses in the condenser 106 and the cycle is repeated.

Referring to FIG. 3, an alternative EPB-CCRS 302 can include the compressor bypass circuit 204 which includes solenoid control valve 208 and the pair of check valves 210 that allow refrigerant to bypass the compressor 104, if pushing the refrigerant through the compressor 104 is not possible or feasible. To bypass the compressor 104, the optional solenoid control valve 208 is shut off inhibiting refrigerant flow to the compressor 104 and the check valves 210 are enabled allowing refrigerant to flow through the check valves 210 into the inlet of the condenser 106, while preventing backflow into the compressor outlet 103 via check valve 210. When operating in a closed circuit refrigeration configuration, EPB- CCRS 302 will operate generally according to FIG. 3 with the compressor bypass circuit 204, including the head pressure control mechanism, but for the by-pass arrangement of the check valves 210.

Referring still to FIG. 3, TMS 300 can include an optional ejector-pump assisted Open-Circuit Refrigeration System (EPB-OCRS) 312. This example implementation of TMS 300 (i.e., with EPB-OCRS 312) can provide closed-circuit refrigeration for low heat loads 118 over long time intervals and open-circuit refrigeration for refrigeration of high heat loads 120 over short time intervals (relative to the interval of refrigeration of low heat load 150).

The EPB-OCRS 312 has a back-pressure regulator 314 coupled between the liquid separator 330 and the compressor 104, by a refrigerant conduit 320, with an optional recycle conduit 316. An exhaust line 318 is coupled to the back-pressure regulator 314 to vent refrigerant. When TMS 300 includes the EPB-OCRS 312 with the back-pressure regulator 314 and is operating in a closed-circuit refrigeration and the low heat load 118 is applied, the TMS 300 is configured to provide refrigeration to the low heat load 118. In this instance, the control system 999 produces signals to cause the back-pressure regulator 314 to be placed in an OFF state (i.e., closed). With the back-pressure regulator 314 closed, the EPB-CCRS 302 provides cooling duty to handle the low heat load 118. On the other hand, when a high heat load 120 is applied, a mechanism such as the control system 999 causes the TMS 300 to operate in both a closed and open cycle configuration.

The closed-circuit portion is similar to that described above, except that the evaporator 116 in this case may operate within a threshold of a vapor quality, (e.g., provided that the liquid separator 330 captures incidental non-evaporated liquid). The liquid separator 330 receives a two-phase mixture and the compressor 104 receives saturated vapor from the liquid separator 330.

When the TMS 300 operates with the open cycle, this causes the control system 999 to be configured to cause the back-pressure regulator 314 to be placed in an ON position, thus opening the back-pressure regulator 314 to permit the back-pressure regulator 314 to discharge vapor through the exhaust line 318. The back-pressure regulator 314 maintains a back-pressure at an inlet (i.e., refrigerant conduit 320) to the back-pressure regulator 314, according to a set point pressure, while allowing the back-pressure regulator 314 to discharge refrigerant vapor through the exhaust line 318, without returning the discharged vapor to the receiver 110 through the recycle conduit 316.

The EPB-OCRS 312 operates like a thermal energy storage (TES) system, increasing cooling capacity of the TMS 300 when a pulsing heat load (e.g., high heat load 120) 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 the high heat load 120. The back-pressure regulator 314 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 318 is governed by the set point pressure used at the input to the back-pressure regulator 314.

When the high heat load 120 is no longer in use or its temperature is reduced, this occurrence is sensed by a sensor (not shown) and a signal from the sensor (or otherwise, such as communicated directly by the high heat load 120) is sent to the control system 999. The control system 999 is configured to partially or completely close the back-pressure regulator 314 by changing the set point pressure (or otherwise), partially or totally closing the exhaust line 318 to reduce or cut off exhaust refrigerant flow through the exhaust line 318. When the high heat load 120 reaches a desired temperature or is no longer being used, the back pressure regulator 314 is placed in the OFF state and is thus closed, and EPB-CCRS 302 continues to operate, as needed.

The provision of the EPB-CCRS 302 helps to reduce the amount of exhausted refrigerant. Generally, the TMS 300 uses the compressor 104 to save 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 EPB-OCRS 312 could be configured to operate in modes where the compressor 104 is turned off and the EPB-OCRS 312 operates in open-circuit mode only (such as in fault conditions in the circuit or cooling requirements).

The EPB-OCRS 312 could generally also include the control system 999 that produces control signals (based on sensed thermodynamic properties) to control operation of the pump 112 and solenoid control valve 124, etc., as needed, as well as the compressor 104 and back-pressure regulator 314. Control system 999 may receive signals, process received signals and send signals (as appropriate) from/to the solenoid control valve 124, and from/to a motor of the pump 112 and a motor (not shown) of the compressor 104 changing their speeds, shutting the pump 112 or compressor 104 off or starting them, etc. The pump 112 can reduce both overall size and weight relative to a conventional refrigeration system sized for the expected heat load(s), while extracting excess heat energy from both low heat loads and high heat loads.

Referring still to FIG. 3, the TMS 300 (operating with the EPB-OCRS 312) can include an optional, additional evaporator 116 attached between the suction inlet 309 of the ejector 310 and the liquid-side outlet 305 of the liquid separator 330. Alternatively, a single evaporator 116 can be attached between the suction inlet 309 of the ejector 310 and the liquid-side outlet 305 of the liquid separator 330. An advantage of this arrangement is the presence of an elevated, saturated suction temperature with respect to the evaporating temperature. In this arrangement, the ejector 310 “pumps” the refrigerant liquid at a higher vapor quality compared with the system arrangement of FIG. 5. While this may result in higher pressure differential across the ejector 310 and more often pump engagement, the pumping power is still negligible compared with the compressor power. In this alternative evaporator arrangement and the EPB-OCRS 312 with back-pressure regulator 314, the EPB- CCRS 302 provides cooling for low heat loads 118 over long time intervals while the EPB- OCRS 312 provides cooling for high heat loads 120 over short time intervals. The closed- circuit refrigeration operation this arrangement is substantially similar as those previously described. On the other hand, when a high heat load 120 is applied, the control system 999 causes the TMS 300 to operate in both a closed and open cycle configuration substantially similar as previously described.

When the subcooling circuit 212 is included (along with the EPB-OCRS 312), this alternative arrangement reduces the risk of pump 112 cavitation as may be present. The condenser 106 provides subcooling through the entire operating range. One way to minimize pump 112 cavitation is to increase the liquid subcooling. The heat rejection processing is executed in plural processes. A first process occurs in the condenser 106 and a second process occurs in a subcooler 214 (e.g., an internal or external heat exchanger, for example). In the condenser 106, the refrigerant condenses and maintains a zero or near zero subcooling. The condensed refrigerant, which may or may not contain some vapor, is transported to the receiver 110. Liquid from the receiver 110 is directed to the subcooler 214 that provides a set value of subcooling to the refrigerant (i.e., reduces the refrigerant temperature by a given number of degrees below the refrigerant boiling temperature). If the ambient conditions reduce the discharge/condensation pressure below the limit and/or the pressure differential across the motive nozzle is below the limit, the head pressure control mechanism, as discussed above, is engaged. When the TMS 300 includes the subcooling circuit 212 and the EPB-OCRS 312 with the back-pressure regulator 314, and when a high heat load 120 is applied, a mechanism such as the control system 999 causes the TMS 300 to operate in both a closed and open cycle configuration.

In some aspects, the TMS 300 includes multiple evaporators 116 (e.g., multiple sections as previously described) along with the EPB-OCRS 312 with the back-pressure regulator 314. In some aspects, there can be a separate EPB-OCRS 312 for each section (with each section having an optional solenoid valve 124, ejector 310, evaporator 116, and liquid separator 330). The outlet 115 of the pump 112 provides refrigerant liquid to multiple solenoid control valves 124 coupled to the multiple motive inlets 307 of multiple ejectors 310 Ejector outlets 311 of ejectors 310 are coupled to inlets 121 of the multiple evaporators 116 and the outlet 123 of the evaporators 116 are coupled to the inlets 301 of multiple liquid separators 330. Thus, each section has its own solenoid control valve 124, an ejector 310, an evaporator 116, and a liquid separator 330. Control system 999 receives signals from pressure sensors (not shown) that sense the motive inlet 307 to the compressor 104 suction pressure differential. The control system 999 generates a signal for the solenoid control valves 124 to control refrigerant flow into the ejectors 310 and evaporators 116.

Alternatively, each solenoid control valve 124 can be configured to control refrigerant flow into each ejector 310 and each evaporator 116, individually provided that each ejector 310 is equipped with its own pressure differential sensor to deal with differences built-in cold plates (not shown) of the evaporators 116. Additionally, one pump 112 can be used for all sections; however, individual pumps 112 can be used as well. A common solenoid control valve 124, or a common ejector 310, or a common liquid separator 330 may be used as well. With this arrangement, and when a high heat load 120 is applied, the control system 999 operates the TMS 300 in both a closed and open cycle configuration as previously described.

The one or more evaporators 116 can be loaded differently. In this case each circuit (or some circuits) may have its own pump 112 to enable control based on a measured or sensed pressure differential across the corresponding ejector 310.

In some cases, with any of the embodiments that include the EPB-OCRS 312, when ambient temperature is low, the needed cooling can be reached by only using the pump 112, while keeping the compressor OFF. The pump 112 pumps liquid refrigerant through the evaporators 116. The refrigerant vapor from the outlet 123 of the evaporators 116 is fed to the liquid separator 330 and at the vapor-side outlet 303 the refrigerant vapor is fed to and discharged from the compressor 104, allowing the refrigerant vapor to circulate through the compressor 104 and reach the condenser 106. The vapor condenses in the condenser 106 and the cycle is repeated.

Referring to FIG. 3, when TMS 300 with the EPB-OCRS 312 includes the compressor bypass circuit 204 with the solenoid control valve 208 and the pair of check valves 210 refrigerant can bypass the compressor 104. This embodiment is particularly useful when pushing refrigerant through the compressor 104 if an OFF state is not practical. To bypass the compressor 104, the solenoid control valve 208 is shut off inhibiting refrigerant flow to the compressor 104 and the pair of check valves 210 are enabled allowing refrigerant to flow through the check valves 210 to the inlet of the condenser 106 while preventing backflow (via check valve 210) into the compressor outlet 103. When a high heat load 120 is applied, the control system 999 operates the TMS 300 in both a closed and open cycle configuration as previously described.

FIGS. 4-7 are schematic diagrams showing alternative configurations for arrangement of evaporators/loads on the integrated open-circuit/closed-circuit refrigeration system, generally applicable to described embodiments. Referring to FIGS. 4-7, additional evaporators that are alternative configurations of the evaporator 116 and heat loads 118, 120 are shown.

In the configuration of FIG. 4, both the low heat load 118 and the high heat load 120 are coupled to (or are in proximity to) a single, i.e., the same, evaporator 116. In the configuration of FIG. 5, each of a pair of evaporators 116 have the low heat load 118 and the high heat load 120 coupled or proximate thereto. In an alternative configuration of FIG. 5, (not shown), the low heat load 118 would be coupled (or proximate) to a first one of the pair of evaporators 116 and the high heat load 120 would be coupled (or proximate) to a second one of the pair of evaporators 116.

In the configurations of FIGS. 6 and 7, the low heat load 118 and the high heat load 120 are coupled (or proximate) to corresponding ones of the pair of evaporators 116. In the configurations of FIGS. 6 and 7, a T-valve 702 (passive or active), as shown, splits refrigerant flow from the receiver 110, into two paths that feed the two evaporators 116. One of these evaporators 116 is coupled (or proximate) to the low heat load 118 and the other of these evaporators 116 is coupled (or proximate to) the high heat load 120. Other configurations are possible.

In the configuration of FIG. 6, the outputs of the evaporators 116 are coupled via conduits 704 to another, second T-valve 702 (active or passive) that has an output that feeds the inlet 301 of the liquid separator 330.

On the other hand, in the configuration of FIG. 7, the outputs of the evaporators 116 are coupled differently. The output of the evaporator 116 that has low heat load 118 feeds the second T-valve 702, whereas the output of the evaporator 116 that has high heat load 120 feeds inlet 301 of the liquid separator 330. In some configurations, the T-valves 702 can be switched (meaning that they can be controlled (automatically or manually) to shut off either or both inlets) or passive meaning that they do not shut off either T-valve 702.

The evaporator 116 is used with the liquid separator 330. 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 “1.”

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 100-300, cooling can be initiated by a variety of different mechanisms. In some embodiments, for example, TMS 100-300 can include temperature sensors attached to heat loads 118, 120 (as will be discussed subsequently).

When the temperature of heat loads 118, 120 exceeds a certain temperature set point (i.e., threshold value), the control system 999 connected to the temperature sensor can initiate cooling of heat loads 118, 120. Alternatively, in certain embodiments, TMS 100-300 operates essentially continuously - provided that the refrigerant fluid pressure within receiver 110 is sufficient - to cool, the low heat load 118 and a temperature sensor attached to high heat load 120 will cause the control system 999 operate the TMS 100-300 when the temperature of high heat load 120 exceeds a certain temperature set point (i.e., threshold value). As soon as receiver 110 is charged with refrigerant fluid, refrigerant fluid is ready to be directed into evaporator 116 to cool the heat loads 118, 120. In general, cooling is initiated when a user of the system or the heat load issues a cooling demand.

Upon initiation of a cooling operation, refrigerant fluid from receiver 110 is discharged from outlet 111, pumped by the pump 112 through solenoid control valve 124, if present, and to the ejector 310.

Once inside the ejector 310, the refrigerant fluid undergoes constant enthalpy expansion from an initial pressure p _r (i.e., the receiver pressure) to an evaporation pressure peout at the outlet 311. In general, the evaporation pressure p _e depends on a variety of factors, e.g., the desired temperature set point value (i.e., the target temperature) at which heat loads 118, 120 is/are to be maintained and the heat input generated by the respective heat loads.

Set points will be discussed below. The initial pressure in the receiver 110 tends to be in equilibrium with the surrounding temperature and is different for different refrigerants. (Operational conditions of the compressor 104 and condenser 106 may be configured to maintain a higher condensing pressure.) 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 TMS 100-300.

The TMS 100-300 is operational as long as the receiver-to-evaporator pressure difference is sufficient to drive adequate refrigerant fluid flow through the ejector 310. After undergoing constant enthalpy expansion in the ejector 310, 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. The two-phase refrigerant fluid mixture is transported via conduit to evaporator 116.

Most of the discussion below pertains to cooling of the high heat load 120. When the two-phase mixture of refrigerant fluid is directed into evaporator 116, the liquid phase absorbs heat from heat loads 118 and/or 120, 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, the temperature of the refrigerant fluid within evaporator 116 (and, nominally, the temperature of high heat load 120) can be controlled to match a specific temperature set-point value for high heat load 120, ensuring that heat loads 118, 120 are maintained at, or very near, a target 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 load temperature within the set tolerances.

In some embodiments, for example, the evaporation pressure of the refrigerant fluid can be adjusted by pressure of the back-pressure regulator 314 to ensure that the temperature of heat loads 118, 120 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 load 49a and/or heat load 49b, especially if they are highly temperature sensitive loads. 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. 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 coupled to another thermal load, and can absorb heat from the additional thermal load during propagation through the heat exchanger.

For open-circuit operation, the refrigerant fluid emerging from evaporator 116 is transported through liquid separator 330. After passing through the liquid separator 330, refrigerant vapor at the vapor-side outlet 303 of the liquid separator 330 is discharged as exhaust, via back-pressure regulator 314 through the exhaust line 318 for TMS 300.

Refrigerant fluid discharge can occur directly into the environment surrounding the TMS 300. Alternatively, in some embodiments, the refrigerant fluid can be further processed; various features and aspects of such processing are discussed in further detail 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 fluid is continuously being discharged from receiver 110, undergoing expansion in ejector 310, flowing continuously through evaporator 116, and being discharged from the TMS 100, while heat loads 118, 120 are being cooled.

During operation of the TMS 100-300, as refrigerant fluid is drawn from receiver 110 and used to cool the high heat load 120, the receiver pressure p _r falls. If the refrigerant fluid pressure p _r in receiver 110 is reduced to a value that is too low, the pressure differential p _r -p _e may not be adequate to drive sufficient refrigerant fluid mass flow to provide adequate cooling of the high heat load 120. Accordingly, when the refrigerant fluid pressure p _r in receiver 110 is reduced to a value that is sufficiently low, the capacity of TMS 100-300 to maintain a particular temperature set point value for heat loads 118, 120 may be compromised. Therefore, the pressure in the receiver 110 or pressure drop across the flow control device 114 (or any related refrigerant fluid pressure or pressure drop in TMS 100- 300) can be an indicator of the remaining operational time. An appropriate warning signal can be issued (e.g., by the control system 999) to indicate that, in a 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 refrigerant fluid pressure in receiver 110 reaches the low-end threshold value.

It should be noted that while in FIGS. 1-3 only a single receiver 110 is shown, in some embodiments, TMS 100-300 can include multiple receivers 110 to allow for operation of the TMS 100-300 over an extended time period. Each of the multiple receivers 110 can supply refrigerant fluid to the system to extend to total operating time period. Some embodiments may include multiple evaporators 116 connected in parallel which may or may not be accompanied by multiple flow control devices 114 and multiple evaporators 116.

As discussed above, by adjusting the pressure p _e of the refrigerant fluid, the temperature at which the liquid refrigerant phase undergoes vaporization within evaporator 116 can be controlled. Thus, in general, the temperature of the heat loads 118, 120 can be controlled by a device or component of TMS 100-300 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 120 individually, because heat absorbed from high heat load 120 is used to drive a constant-temperature evaporation of liquid refrigerant to form refrigerant vapor in 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 evaporator 116 is reached to allow continued heat absorption from high heat load 120 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 high heat load 120.

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 120 to undergo a phase change. To ensure that TMS 100-300 operates efficiently, the 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 120 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 and dryout and mist regions 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 120, 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 high heat load 120 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 nearly equal to the critical vapor quality.

Another important operating consideration for TMS 100-300 is the mass flow rate of refrigerant fluid within the TMS 100-300. 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 load 120, TMS 100-300 operates efficiently. Each reduction in the mass flow rate of the refrigerant fluid (while maintaining the same temperature set point value for high heat load 120) means that the charge of refrigerant fluid added to receiver 110 initially lasts longer, providing further operating time for TMS 100-300.

Within evaporator 116, the vapor quality of a given quantity of refrigerant fluid varies from the inlet 121 of the evaporator 116 (where vapor quality is lowest) to the outlet 123 of the evaporator 116(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 the 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 120 is maintained within a relatively small tolerance, TMS 100-300 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, ideally without entering the mist and dryout regions of the refrigerant phase diagram. At the same time requirements for CCRS efficient operation would be taken into consideration as well. In addition, generally the compressor 104 does not work well with liquids at its inlet 101. Accordingly, operation of TMS 100-300, as close as possible to the critical vapor quality, is desirable.

In general, a wide variety of different measurement and control strategies can be implemented in TMS 100-300 to achieve the control objectives discussed above. These strategies are presented below. Generally, the pump 112 is connected to a measurement device or sensor (not shown). The measurement device provides information about the thermodynamic quantities upon which adjustments of 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 and their mixtures can be used in TMS 100- 300. Depending on the 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, the 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 the 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, the heat loads 49a- 49b (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.

FIG. 8 is a block diagram of an example control system or controller, such as control system 999. The embodiment shown in FIG. 8 of control system 999 is for exemplary purposes only and describes certain components as separate but connected. Other example implementations of a control system can be implemented, for example, as a programmable logic controller, a microprocessor (or multiple microprocessors, e.g., on a computer board), an application specific integrated circuit (ASIC) or other hardware. Other forms of controllers or control systems are also contemplated in the present disclosure, such as mechanical controllers, pneumatic controllers, hydraulic controllers, or electro-mechanical controller, or a combination thereof.

Referring to FIGS. 1-3 and 8, control system 999 can adjust solenoid control valves 124 based on measurements of one or more of the following system parameter values: the pressure drop (pr-p _e ) across solenoid control valves 124, the pressure drop across evaporator 116, the refrigerant fluid pressure in receiver 110 (p _r ), 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, or P _e -in and P _e -out pressures at the inlet and outlet of the ejector 310.

To adjust solenoid control valves 124 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 and their mixtures 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 the atmosphere. Any liquid captured in the liquid separator is recycled back into the OCRS (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 inlet 121 of the evaporator 116.

Various combinations of sensors can be used to measure thermodynamic properties of the TMS 100-300 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.

Referring to FIG. 8, the example control system 999 includes a processor 1302, memory 1304, storage 1306, and I/O interfaces 1308, all of which are connected/coupled together via a bus 1310. Control system 999 can be used with any of the embodiments discussed herein, e.g., any of FIGS. 1 to 3.

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., solenoid control valve 124) 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. Any two of devices, such as pressure sensors, upstream and downstream from a control device, can be configured to measure information about a pressure differential pr-p _e 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 116. 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 the evaporator inlet 121 or the evaporator outlet 123 of evaporator 116 or between the evaporator inlet 121 and the evaporator outlet 123. 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 118,120, which measures temperature information for the heat loads 118,120 and transmits an electronic signal corresponding to the measured information. An optional temperature sensor can be adjacent to the evaporator outlet 123 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 the TMS 100-300 and the saturated vapor temperature of the refrigerant fluid defined by the refrigerant pressure at the measurement point in the TMS 100- 300. To determine the superheat associated with the refrigerant fluid, the 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 the actual temperature of the refrigerant fluid, and then calculates the superheat associated with the refrigerant fluid as the difference between the 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 TMS 100-300. As one example, thermocouples and thermistors can function as temperature sensors in TMS 100-300. Examples of suitable commercially available temperature sensors for use in TMS 100-300 include, but are not limited to, thermocouple surface probes.

TMS 100-300 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 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.

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 the 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 the TMS 100-300. 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 the TMS 100-300, 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-p _e across a control device and to transmit an electronic signal corresponding to the measured pressure difference information. Two sensors can effectively measure p , 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 measures and transmits 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 a measurement device connected to a solenoid control valve 124, and any one or various combination of two sensors can correspond another 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 solenoid control valve 124. The first and second control devices 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 embodiments where control devices are 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 flow control device 114 to control the vapor quality of the refrigerant fluid in the TMS 100-300.

During operation of the TMS 100-300, 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.

To adjust any of the control devices, e.g., pump 112, solenoid control valve 124, compressor 104, back-pressure regulator 314, etc., 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 one or more of the control devices to adjust the operating state of the TMS 100, 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 one or more of the control devices to adjust the operating state of the TMS 100, 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 one or more control devices to adjust the operating state of the TMS 100-300, 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 one or more of the control devices to adjust the operating state of the TMS 100-300, 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 one or more of the control devices to adjust the operating state of the TMS 100-300, 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.

In general, the systems 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 the additional thermal loads can have an associated heat exchanger.

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 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.

Further, eliminating (or nearly eliminating) the refrigerant vapor from the refrigerant fluid stream entering the 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 the 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. 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 the 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 the TMS 100-300. 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 the 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 120. For example, high heat load 120 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 load 120 and/or heat loads 118,120 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.

FIG. 9 is a schematic diagram of an example of a thermal management system that includes a power generation apparatus. In some embodiments, the TMS 100-300 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. 9 shows an integrated power generation apparatus and TMS 300. The TMS 300 has the receiver 110, pump 112, and the evaporator 116 coupled to back-pressure regulator 314, and includes or is coupled to an engine 1402 with an inlet 1404 that receives the stream of waste refrigerant vapor from exhaust line 318. Engine 1402 can combust the waste refrigerant vapor 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 TMS 300, 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 1402 to generate electrical power, e.g., by using the energy to drive a generator (not shown). The electrical power can be delivered via electrical connection to high heat load 120 to provide operating power for the load. For example, in certain embodiments, high heat load 120 includes one or more electrical circuits and/or electronic devices, and engine 1402 provides operating power to the circuits/devices via combustion of refrigerant fluid. Byproducts 1408 of the combustion process can be discharged from engine 1402 via an exhaust conduit 1406.

Various types of engines and power-generating devices can be implemented as engine 1402 in TMS 300. In some embodiments, for example, engine 1402 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 1402 is a gas turbine engine, and the waste refrigerant fluid is introduced via the engine inlet to the afterburner of the gas turbine engine. As discussed above, in some embodiments, TMS 300 can include phase separator (not shown) positioned upstream from engine 1402. Phase separator functions to prevent liquid refrigerant fluid from entering engine 1402, which may reduce the efficiency of electrical power generation by engine 1402. Although TMS 300 is shown integrated with the power generation apparatus 1400 in FIG. 9, TMS 100 and 200 can likewise be integrated into power generation apparatus 1400 in a similar manner.

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 start-up, the compressor 104 and a device (usually the fan 108) 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.

FIG. 10 is a schematic diagram of an example of directed energy system that includes a thermal management system. Referring to FIGS. 1-3 and 10, the thermal management systems 100-300 and methods disclosed herein can be implemented as part of (or in conjunction with) a directed energy systems 1500 such as high energy laser systems. Due to their nature, directed energy systems 1500 typically present a number of cooling challenges, including certain heat loads for which temperatures are maintained during operation within a relatively narrow range.

FIG. 10 shows one example of a directed energy system 1500, specifically, a high energy laser system. Directed energy laser system 1500 includes a bank of one or more laser diodes 1502 and an amplifier 1504 connected to a power source 1506. During operation, laser diodes 1502 generate an output radiation beam 1508 that is amplified by amplifier 1504, and directed as output beam 1510 onto a target 1512. Generation of high energy output beams 1510 can result in the production of significant quantities of heat. Certain laser diodes, 1502 however, are relatively temperature sensitive, and the operating temperature of such diodes 1502 is regulated within a relatively narrow range of temperatures to ensure efficient operation and avoid thermal damage. Amplifiers 1504 are also temperature- sensitive, although typically less sensitive than diodes 1502.

Referring to FIGS. 1-3 and 10, to regulate the temperatures of various components of directed energy systems 1500 such as laser diodes 1502 and amplifier 1504, such systems can include components and features of the TMS 100-300 disclosed herein. In FIG. 10, evaporator 116 is coupled to laser diodes 1502, while the evaporator 116 or multiple evaporators 116 are coupled to the amplifier 1504. The other components of the thermal management systems 100-300 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 1500. Laser diodes 1502, due to their temperature- sensitive nature, effectively function as high heat load 120 in the high energy laser system 1500, while amplifier 1504 functions as low heat load 118.

The high energy laser system is one example of the directed energy system 1500 that can include various features and components of the thermal management systems 100-300 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.

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.