INTEGRATED FLOW SEPARATOR AND PUMP-DOWN VOLUME DEVICE FOR USE IN A HEAT EXCHANGER

BACKGROUND

This invention relates generally to the field of heat exchangers and more specifically to phase separators and pump-down volumes for parallel flow heat exchangers.

A heat exchanger comprises a fluid flow device in which an external fluid, usually air, flows across an internally piped fluid, usually a refrigerant, to transfer heat. When used in conjunction with a heat pump system, the heat exchanger can function to add heat to the external fluid as a condenser, or can add heat to the internal fluid as an evaporator. When functioning as an evaporator, the refrigerant typically enters the heat exchanger as a two-phase fluid comprising liquid and vapor. When functioning as a condenser, the refrigerant typically enters the heat exchanger as a single-phase fluid substantially comprising vapor. In a parallel flow heat exchanger, the internal fluid flows through a plurality of generally parallel circuits, the openings and outlets of which are connected by respective headers or manifolds. Parallel flow heat exchangers achieve efficient heat transfer in a compact size by increasing the surface area of the refrigerant within the circuits. Further advancements in efficiency and size of parallel flow heat exchangers have been achieved with the development of mini-channel or micro-channel heat exchangers (MCHX) in which the size of the parallel circuits is substantially reduced such that each only contains a small fraction of the total refrigerant volume of the heat exchanger. Thus, the internal volume of the refrigerant within the circuits is reduced.

Efficiency of parallel flow heat exchangers, particularly in MCHX exchangers, is, however, inhibited by phase mal-distribution and flow mal-distribution of the refrigerant within the headers and circuits. Phase mal-distribution can be caused by a number of factors, but commonly arises due to the discrepancy in flow velocities between the phases of two-phase refrigerant fluid, which have different densities, entering a liquid header during evaporator operation. Particularly, in fast moving two-phase refrigerant, momentum carries droplets of heavier liquid phase refrigerant further than the lighter vapor phase refrigerant. Thus, the parallel heat exchange circuits near the manifold entrance receive refrigerant primarily in the vapor phase, while circuits further away receive primarily liquid refrigerant. Conversely, in slow moving two-phase refrigerant, liquid phase refrigerant remains near circuits close to the manifold entrance, while the

vapor phase refrigerant is carried to circuits further away. Thus, for example, some circuits are underutilized for converting liquid-phase refrigerant to vapor-phase refrigerant in an evaporator. Similarly, flow mal-distribution arises when refrigerant, typically single-phase refrigerant, enters a header through an opening located closer to some circuits than others. A greater volume of the refrigerant tends to enter the circuits closer to the opening, with the circuits further away receiving a volume of refrigerant below their capacities to conduct refrigerant. Thus, for example, refrigerant is unequally distributed between the individual circuits in a condenser and some circuits are underutilized for converting vapor-phase refrigerant to liquid-phase refrigerant. With either phase or flow mal-distribution, efficient heat transfer between the refrigerant and the external air is degraded as evaporation or condensation of the liquid refrigerant is not optimally carried out in all heat exchange circuits. These problems are exacerbated by MCHX exchangers that have very small entrances to each heat exchange circuit.

Furthermore, as described above, compared to conventional heat exchangers, parallel flow heat exchangers and MCHX heat exchangers provide much less internal volume for refrigerant storage. Occasionally, a heat pump system must go to a pump- down state, wherein one of the headers is closed off and the refrigerant in the heat pump system is pumped into one of the heat exchangers such that service or maintenance may be performed on the heat pump system. Parallel flow and MCHX heat exchangers often do not have sufficient internal volume to allow the heat pump system to go to a full pump down state due to the size of each circuit and the small internal volume.

SUMMARY

Exemplary embodiments of the invention include a phase separator and fluid storage volume device for a heat exchanger. The device comprises a vessel, a vapor tube, a liquid tube, an access tube and a flow regulating device. The vessel comprises a first chamber, a second chamber, and a divider separating the first chamber from the second chamber. The vapor tube extends from within the second chamber, through the divider and the first chamber to outside the first chamber. The vapor tube also includes holes between an inlet and an outlet of the tube within the first chamber. The liquid tube extends from within the second chamber to outside of the second chamber. The access tube connects to the second chamber. The flow regulating device is disposed within the vapor tube to provide phase separation between refrigerant traveling between the first chamber and the second chamber within the vapor tube.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of heat exchangers incorporating refrigerant vessels of the present invention integrated into a heat pump system operable in heating and cooling modes to condition a space. FIG. 2A shows a heat exchanger operating as a condenser for use in the heat pump system of FIG. 1, wherein the heat exchanger includes a refrigerant vessel operating as a stop valve.

FIG. 2B shows a heat exchanger operating as an evaporator for use in the heat pump system of FIG. 1, wherein the heat exchanger includes a refrigerant vessel operating as a phase separator.

FIG. 3 shows a heat exchanger operating as a pump-down storage volume for the heat pump system of FIG. 1, wherein the heat exchanger includes a refrigerant vessel operating as a storage volume.

FIG. 4 shows another embodiment of a heat exchanger incorporating a refrigerant vessel of the present invention for use in the heat pump system of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows a schematic view of heat pump system 10 incorporating refrigerant flow control vessels 12 and 14 of the present invention. System 10 comprises compressor 16, valve 18, outdoor heat exchanger 20, expansion devices 22 and indoor heat exchanger 24, which are connected in series through refrigerant lines 25A - 25C to form a vapor-compression circuit. Valve 18 comprises a four way reversing valve, as is known in the industry, to pump refrigerant from compressor 16 through the circuit in forward and reverse directions. As such, outdoor heat exchanger 20 and indoor heat exchanger 24 are able to operate as both condensers and evaporators, and system 10 is operable to provide conditioned air to space 26 that is either heated or cooled. System 10 is configured as a split system in which heat exchanger 24 is positioned within space 26, and compressor 16, heat exchanger 20 and expansion device 22 are positioned outside space 26. In other embodiments, expansion device 22 may be placed inside of space 26 on line 25B adjacent vessel 14. Space 26 comprises a building, home or any other enclosed space in which conditioned air is desired to be provided. System 10 is connected to a control system, which includes controller 28, outdoor fan 30, indoor fan 32, outdoor sensor 34 and indoor sensor 36. Based upon factors such as temperature and humidity sensed by sensors 34 and 36, controller 28 operates fans 30 and 32, compressor 16 and valve 18 to provide either heated or cooled conditioned air to space 26.

Furthermore, heat pump system 10 includes service valves 38 and 40 which controller 28 operates in conjunction with compressor 16 to perform a pump-down operation wherein refrigerant contained within heat pump system 10 is collected within a single heat exchanger and refrigerant vessel. In the heating mode, as shown in FIG. 1, outdoor heat exchanger 20 operates as an evaporator and indoor heat exchanger 24 operates as a condenser. Compressor 16 compresses a refrigerant to a high pressure and to a high temperature above that of indoor air Ai such that the refrigerant is comprised substantially of superheated vapor. Any suitable refrigerant as is known in the industry may be used such as R-22 or R-410A refrigerants. Valve 18 operates to supply the evaporated refrigerant to exchanger 24 within space 26 through line 25A, while controller 28 activates fan 32 to accelerate relatively cooler indoor air Ai across heat exchanger 24. Heat exchanger 24 increases the surface area of the refrigerant within a plurality of interior flow circuits such that indoor air Ai and the refrigerant are better able to exchange heat. The refrigerant cools and condenses to a saturated liquid having a slightly lower temperature than before while still at a high pressure, rejecting heat to space 26. Indoor air Ai absorbs heat from the refrigerant within exchanger 24 as indoor air Ai is circulated through heat exchanger 24 and space 26 by fan 32. From heat exchanger 24, the refrigerant is passed through line 25B and expansion device 22, which rapidly lowers the pressure of the refrigerant and rapidly lowers the temperature of the refrigerant to below that of outside air Ao such that the refrigerant converts to a two-phase state of liquid and vapor in a flash evaporation process. Under pressure from compressor 16, the cold refrigerant continues to flow into outdoor heat exchanger 20, where controller 28 activates fan 30 to accelerate relatively warmer outdoor air Ao across heat exchanger 20. The refrigerant is vaporized by the relative warmth of outdoor air A ₀ such that the refrigerant evaporates and absorbs heat to comprise a saturated vapor. The hot vapor is then drawn into the suction port of compressor 16 through line 25C where it is heated and compressed into a high temperature, high pressure vapor such that the cycle can be repeated.

In the cooling mode, the process is reversed and indoor heat exchanger 24 operates as an evaporator and outdoor heat exchanger 20 operates as a condenser to provide cooling to space 26. As such, the arrows on lines 25A, 25B and 25C of FIG. 1 would be reversed to indicate reverse flow of the refrigerant. While providing cooled air to space 26, compressor 16 compresses a refrigerant to a high pressure and to a high temperature above that of outdoor air A ₀ such that the refrigerant is comprised

substantially of superheated vapor. The evaporated refrigerant is discharged from compressor 16 where valve 18 operates to supply the refrigerant to heat exchanger 20, now acting as a condenser, through line 25C while controller 28 activates fan 30 to accelerate relatively cooler outdoor air Ao across heat exchanger 20. The refrigerant cools and condenses to a saturated liquid having a slightly lower temperature than before while still at a high pressure. From heat exchanger 20, the refrigerant is passed through expansion device 22, which rapidly lowers the pressure and rapidly lowers the temperature of the refrigerant to below that of indoor air Ai such that the refrigerant converts to a two-phase state of liquid and vapor in a flash evaporation process. Under pressure from compressor 16, the cold refrigerant continues to flow into heat exchanger 24, now acting as an evaporator, through line 25B where controller 28 activates fan 32 to accelerate relatively warmer indoor air Ai across evaporator 24. Indoor air Ai dumps heat to the refrigerant within heat exchanger 24 as indoor air Ai passes over heat exchange circuits of heat exchanger 24. The refrigerant evaporates and absorbs heat from the relatively warmer indoor air Ai such that the refrigerant is vaporized to a saturated vapor. The hot vapor is then drawn into compressor 16 through line 25 A where it is compressed and heated into a high temperature, high pressure vapor such that the cycle can be repeated.

In either operating mode, system 10 utilizes the pressure differentials produced by compressor 16 and expansion device 22, and the relative heat differentials produced between the air and the refrigerant within heat exchangers 20 and 24 to move heat into and out of space 26. In particular, system 10 relies on the ability of the vapor- compression circuit to change the refrigerant from a liquid to a vapor and vice versa. The efficiency of system 10 depends on the efficiency with which heat exchangers 20 and 24 are able to transfer heat to and from indoor air Ai and outdoor air A ₀ , which depends on the refrigerant being in the proper phase within the evaporator and condenser. For example, when heat exchangers 20 and 24 operate as evaporators, it is advantageous for the saturated vapor from two-phase refrigerant to be separated from the saturated liquid so that more of the liquid is able to convert to vapor while traveling through the heat exchange circuits, thus reducing or eliminating phase mal-distribution and its effects. Likewise, when heat exchangers 20 and 24 operate as condensers, it is advantageous for superheated vapor from single-phase refrigerant to be equally distributed to the heat exchange circuits, thus reducing or eliminating flow maldistribution and its effects. Within system 10, refrigerant vessels 12 and 14 segregate

flow of liquid and vapor phase refrigerant entering heat exchangers 20 and 24, respectively, to improve distribution of the refrigerant to the exchange circuits, thus improving the heat transfer efficiency of the exchangers. Refrigerant vessels 12 and 14 operate as phase-separators to separate saturated liquid from saturated vapor when heat exchanger 20 and heat exchanger 24 operate as evaporators within a heat pump system. Refrigerant vessels 12 and 14 also operate as stop valves to improve vapor and liquid flow through heat exchanger 20 and heat exchanger 24 when operating as condensers within a heat pump system. In other embodiments, refrigerant vessels 12 and 14 also provide a phase-separating function between sub-critical refrigerant and super-critical refrigerant when heat exchangers 20 and 24 operate under trans-critical conditions such as within a gas cooler.

Additionally, vessels 12 and 14 provide a pump-down volume for system 10 such that refrigerant within the vapor-compression circuit can be collected in order to, among other things, perform maintenance on system 10. For example, during a pressure-side pump-down operation, refrigerant from the evaporator heat exchanger, e.g. exchanger 20, is delivered to the condenser heat exchanger, e.g. exchanger 24. Valve 38, which is positioned between condenser heat exchanger 24 and expansion device 22, is closed, and compressor 16 is activated to evacuate refrigerant from exchanger 20 and pump the refrigerant to exchanger 24 whereby valve 38 prevents refrigerant from leaving exchanger 24. As such, refrigerant is removed from the vapor-compression circuit between valve 38 and valve 18, including exchanger 20 and compressor 16. Thus, these components can be removed from system 10 without loss of refrigerant. Depending on the position of valve 18, refrigerant can also be evacuated from within heat exchanger 24 and stored in heat exchanger 20 utilizing valve 40. Vessels 12 and 14 provide additional volume to exchangers 20 and 24, respectively, to provide additional storage space, which is often unavailable in MCHX heat exchangers, to complete a pump-down operation. Vessels 12 and 14 thus provide system 10 with phase separating devices and pump-down volumes that increase the efficiency and flexibility of heat exchangers 20 and 24.

FIG. 2A shows heat exchanger 20 and vessel 14 of system 10 from FIG. 1 operating as a condenser such as during a cooling operation of system 10. Heat exchanger 20 includes vapor header 42, liquid header 44, liquid header insert 46 and heat exchange channels 48. Vessel 12 includes expansion device 22, vapor tube 50, liquid tube 52, vessel body 54, divider 56, access tube 58 and flow regulating device 62.

Heat exchange channels 48 comprise a plurality of generally parallel flow circuits that define channels of communication between vapor header 42 and liquid header 44. Each cannel comprising channels 48 typically comprises a tube or some other fluid communicating member. In the embodiment shown, channels 48 comprise vertical, single-pass, parallel flow circuits, but in other embodiments horizontal flow circuits or circuits oriented at any other angle may be used. Likewise, in other embodiments, channels 48 can comprise multi-pass or multi-circuit heat exchange channels, or MCHX channels. For example, in one embodiment, channels 48 comprise mini-channel heat exchange channels having hydraulic diameters in the range of approximately 0.7 mm to approximately 2.0 mm. In another embodiment, channels 48 comprise micro-channel heat exchange channels having hydraulic diameters less than approximately 0.7 mm. In yet another embodiment, channels 48 comprise micro-channel heat exchange channels having varying hydraulic diameters within the above-referenced approximate rage.

In the embodiment shown, vapor header 42 comprises an elongate, horizontal, hollow body that extends across the tops of heat exchange channels 48, while liquid header 44 comprises an elongate, horizontal, hollow body that extends across the bottoms of heat exchange channels 48. Thus, the top ends of channels 48 are in fluid communication with vapor header 42, and the bottom ends of channels 48 are in fluid communication to liquid header 44. Vapor header 42 is opened at a first end A such that vapor header 42 is in fluid communication with line 25C, which is under pressure when heat exchanger 20 is operating as a condenser. Vapor header 42 is open at second end B such that vapor header 42 is in fluid communication with vapor tube 50. Liquid header 44 is open at a first end C such that liquid header 44 is in fluid communication with liquid tube 52. Liquid header 44 is closed at a second end D. Liquid header insert 46 is positioned within liquid header 44 and is fluidly connected to liquid tube 52. Liquid header insert 46 includes a plurality of holes or perforations such that heat exchange channels 48 are in fluid communication with liquid tube 52. Vapor tube 50 and liquid tube 52 are connected to and are in fluid communication with vessel body 54.

Vessel body 54 comprises a cylindrical hollow body that is integrated into heat exchanger 20 between vapor header 42 and liquid header 44. Divider 56, which comprises a disk-shaped member, is positioned approximately mid-span within vessel body 54 to form vapor volume 66 and liquid volume 68 within vessel body 54. The position of divider 56 is varied based on design needs, but is typically positioned such that liquid volume 68 is equal to the vapor volume 66. In other embodiments, liquid

volume 68 is smaller than vapor volume because liquid is more dense than vapor and therefore requires less space. Exchange of fluid between vapor volume 66 and liquid volume 68 is regulated by flow regulating device 62, which is positioned within vapor tube 50. Vapor tube 50 is open at first end E, which is positioned within liquid volume 68.

Vapor tube 50 is open at second end F, which is connected to vapor header 42. From second end F, vapor tube 50 extends through the entirety of vapor volume 66 and through divider 56. The portion of the body of vapor tube 50 positioned within vapor volume 66, however, includes a plurality of holes 70. As such, vapor tube 50 provides fluid communication between vapor header 42 and both vapor volume 66 and liquid volume 68. Flow regulating device 62 is positioned near first end E of vapor tube 50 inside liquid volume 68 to regulate flow between vapor volume 66 and liquid volume 68.

Liquid tube 52 is open at first end G, which is positioned within liquid volume

68. Liquid tube 52 is open at second end H, which is connected to liquid header 44 and insert 46. Liquid tube 52 comprises a non-perforated body that fluidly connects liquid header 44 and insert 46 with liquid volume 68. Insert 46 extends the length of liquid header 44 adjacent the bottom ends of channels 48. Vessel body 54 also includes access tube 58 positioned along the length of vessel body 54 neat the top of liquid volume 68. Access tube 58 provides an opening within liquid volume 68 and is connected with expansion device 22, which is connected with line 25B to connect heat exchanger 20 with heat exchanger 24.

During cooling operation of system 10, as shown in FIG. 1, heat exchanger 20 operates as a condenser. As a condenser, refrigerant enters heat exchanger 20 at vapor header 42 as high temperature, high pressure vapor refrigerant Ry, indicated by the solid arrows, under pressure from compressor 16. Heat exchange channels 48 cool the refrigerant such that the refrigerant leaves exchanger 20 at access tube 58 as cooler liquid refrigerant R _L , indicated by the outlined arrows. Flow regulating device 62 of refrigerant vessel 12 maintains segregated flow of liquid refrigerant R _L and vapor refrigerant Ry within heat exchange channels 48. Vapor refrigerant Ry enters vapor header 42 at first end A through line 25C. In the cooling mode, valve 18 (FIG. 1) links line 25C with the discharge of compressor 16 such that compressor 16 pumps high pressure vapor refrigerant to exchanger 20. Under pressure from compressor 16, vapor refrigerant Ry disperses throughout vapor header 42, and continues to second end B of vapor header 42, which is connected to vapor tube 50.

Vapor refrigerant R _v continues through vapor tube 50 to flow regulating device 62, whereby flow regulating device 62 prevents vapor refrigerant R _v from entering liquid volume 68. Vapor refrigerant Ry, however, enters vapor volume 66 through holes 70 provided in vapor tube 50. Thus, vapor volume 66, vapor tube 50 and vapor header 42 become pressurized with vapor refrigerant R _v , causing substantially uniform distribution of vapor within header 42.

From vapor header 42, vapor refrigerant Ry also settles into openings within heat exchange channels 48 connected to vapor header 42. Utilizing pressure provided from compressor 16, vapor refrigerant R _v is pushed through channels 48 to liquid header 44 whereby, with the aid of inside air Ai passing across channels 48 (FIG. 1), vapor refrigerant Ry condenses to produce liquid refrigerant R _L within liquid header 44. Insert 46 is provided within liquid header 44 and includes holes to permit liquid refrigerant R _L from liquid header 44 to enter insert 46 and flow into liquid tube 52. Liquid refrigerant R _L continues into liquid volume 68 from liquid tube 52. Liquid volume 68 fills with liquid refrigerant R _L up to access tube 58 and first end E of vapor tube 50. Flow regulating device 62 prevents liquid refrigerant R _L from flowing through vapor tube 50 and entering vapor volume 66. Liquid refrigerant R _L flows through access tube 58, through expansion device 22 and out to line 25B. Thus, refrigerant leaves heat exchanger 20 as high pressure, high temperature liquid refrigerant R _L in an adiabatic state suitable for flash expansion in expansion device 22.

While operating as a condenser, vapor volume 66 is pressurized under the influence of compressor 16, while liquid volume 68 is under depressurization from connection to the suction side of compressor 16 at line 25B. Under condenser operating conditions, when the pressure in vapor header 42 exceeds the pressure in liquid header 44, flow regulating device 62 inhibits liquid refrigerant R _L within liquid volume 68 from flowing through vapor tube 50 and entering vapor volume 66 and vapor header 42. Likewise, flow regulating device 62 inhibits vapor refrigerant Ry within vapor volume 66 from flowing through vapor tube 50 and entering liquid volume 68. Thus, flow regulating device 62 acts as a stop valve. In one embodiment of the invention, flow regulating device 62 is comprised of first accurator 62A and second accurator 62B arranged in a double- accurator configuration. Generally speaking, an accurator comprises a restriction expansion device that converts liquid flowing through the device in a first direction to a vapor, while not converting the liquid to a vapor when flowing in the opposite direction. Accurators may

also provide expansion to vapor flow, depending on the size of the restriction. In one embodiment, first accurator 62A and second accurator 62B comprise any refrigerant expansion device commonly known as an accurator, as is know in the art. For example, such accurators are described in U.S. Pat. No. 3,992,898 to Duell et al.; and U.S. Pat. No. 5,689,972 to Schuster et al., both assigned to Carrier Corporation, Syracuse, New York. First accurator 62A and second accurator 62B are arranged in series within vapor tube 50. The flow restriction orientations of first accurator 62A and second accurator 62B are oriented oppositely within vapor tube 50. For the purposes of explanation, forward flow is defined as flow from liquid volume 68 to vapor volume 66 and reverse flow is defined as flow from vapor volume 66 to liquid volume 68.

First accurator 62A is oriented to permit forward flow of liquid refrigerant R _L from liquid volume 68 to pass through first accurator 62A unrestricted, which also permits any vapor refrigerant R _v present within liquid volume 68 to pass through first accurator 62A unrestricted. Second accurator 62B is oriented in the opposite direction and the orifice within second accurator 62B is sized to expand forward flow of liquid refrigerant R _L , thus preventing liquid refrigerant R _L from entering vapor volume 66. Second accurator 62B is also sized to allow any vapor refrigerant R _v present within liquid volume 68 to enter vapor volume 66. Thus, first accurator 62A and second accurator 62B provide phase separation of refrigerant flowing in the first direction. Second accurator 62B is oriented to permit reverse flow of vapor refrigerant Ry from vapor volume 66 to pass through second accurator 62A unrestricted. Second accurator 62B is also sized to permit any liquid refrigerant R _L present within vapor volume 66 to pass through second accurator 62A. First accurator 62A is oriented in the opposite direction and the orifice within first accurator 62A is sized to expand reverse flow of vapor refrigerant R _v from vapor volume 66 to liquid volume 68. First accurator 62A is also sized to prevent reverse flow of liquid refrigerant R _L from vapor volume 66 to liquid volume 68. Thus, first accurator 62A and second accurator 62B provide phase separation of refrigerant flowing in the second direction.

As such, in the condenser mode, flow regulating device 62 acts as a stop valve to inhibit exchange of vapor and liquid refrigerant between vapor volume 66 and liquid volume 68, while not interfering with the ability of vapor refrigerant Ry to flow through heat exchange channels 48. Small amounts of liquid refrigerant R _L are permitted to escape from vapor volume 66 to liquid volume 68 through the double- accurator arrangement should any liquid refrigerant R _L accumulate in vapor header 66. Vessel 14,

however, provides an alternative path through heat exchanger 20 for liquid refrigerant R _L such that channels 48 are available to condense vapor refrigerant R _v .

In a typical conventional single-pass, parallel flow heat exchanger without vessel 12, second end B of vapor header 42 would be closed off such that all vapor would enter into the heat exchange circuits. Additionally, first end C of liquid header 44 would be directly connected to line 25B to carry liquid refrigerant away from the heat exchanger. Vapor refrigerant entering a conventional vapor header as vapor would suffer from flow mal-distribution. The influent vapor would immediately begin to flow into the heat exchange coils such that a greater volume of vapor refrigerant would tend to condense in the circuits closer to the end of the vapor header near the line extending from the compressor (e.g. first end A of vapor header 42). Circuits nearer the distal end of the vapor header (e.g. second end B of vapor header 42) would see a reduced throughput of vapor refrigerant. Thus, distribution of vapor refrigerant with the heat exchange coils would be unequal and the efficiency of the heat exchanger would be degraded. It is expected that refrigerant vessel 12 of the present invention diminishes these effects by allowing vapor refrigerant Ry to equalize pressure within vapor header 42, thus promoting better distribution of vapor refrigerant R _v into heat exchange channels 48. Refrigerant vessel 12 also reduces the amount of any vapor refrigerant R _v from entering liquid header 44. Thus, liquid header 44 fills with a greater amount of liquid refrigerant R _L and more liquid refrigerant is distributed out to access tube 58.

FIG. 2B shows heat exchanger 20 and vessel 12 operating as an evaporator such as during heating operation of system 10. After having passed through expansion device 22, refrigerant enters vessel 12 at access tube 58 as saturated liquid refrigerant R _L , indicated by outlined arrows, and saturated vapor refrigerant Ry, indicated by solid arrows. Vessel 12, including flow regulating device 62, separates vapor refrigerant R _v from liquid refrigerant R _L such that only liquid refrigerant R _L is evaporated in heat exchange channels 48. Thus, only vapor refrigerant Ry leaves heat exchanger 20 at line 25C.

In the heating mode of system 10, liquid refrigerant R _L from heat exchanger 24 flows towards heat exchanger 20 within line 25B under pressure from compressor 16 (FIG. 1). Expansion device 22 expands liquid refrigerant R _L such that both saturated liquid refrigerant R _L and saturated vapor refrigerant Ry enters access tube 58. Access tube 58 empties into liquid volume 68 where liquid refrigerant R _L gravitates toward the

bottom of liquid volume 68 and liquid tube 52. Vapor refrigerant R _v rises towards the top of liquid volume 68 and flow regulating device 62.

From liquid tube 52, liquid refrigerant R _L enters insert 46 inside liquid header 44. Insert 46 comprises an elongate tube that extends the width of liquid header 44 and includes holes that permit liquid refrigerant R _L to escape into liquid header 44. The holes further expand liquid refrigerant R _L as the refrigerant enters heat exchange channels 48 where, with the aid of outside air Ao passing across channels 48, liquid refrigerant R _L is finally evaporated into vapor refrigerant Ry, where it collects in vapor header 42. Additionally, the overall size of insert 46 can be used to take up space within liquid header 44 to improve flow distribution of liquid refrigerant R _L into heat exchange channels 48, reducing flow mal-distribution effects.

While operating as an evaporator, liquid volume 68 is pressurized under the influence of compressor 16, while vapor volume 42 is under depressurization from connection to the suction side of compressor 16 at line 25C. Under evaporator operating conditions, when the pressure in liquid header 44 exceeds the pressure in vapor header 42, flow regulating device 62 inhibits liquid refrigerant R _L within liquid volume 68 from flowing through vapor tube 50 and entering vapor volume 66 and vapor header 42. Flow regulating device 62, however, permits vapor refrigerant R _v within liquid volume 68 to enter vapor volume 66. As discussed above, in one embodiment, flow regulating device 62 is comprised of first accurator 62A and second accurator 62B arranged in a double-accurator configuration. First accurator 62A and second accurator 62B are arranged in series within vapor tube 50. The flow restriction orientations of first accurator 62A and second accurator 62B are oriented oppositely within vapor tube 50. For the purposes of explanation, forward flow is defined as flow from liquid volume 68 to vapor volume 66 and reverse flow is defined as flow from vapor volume 66 to liquid volume 68.

First accurator 62A is oriented to permit forward flow of liquid refrigerant R _L from liquid volume 68 to pass through first accurator 62A unrestricted. First accurator 62A also permits vapor refrigerant R _v present within liquid volume 68 to pass through first accurator 62A unrestricted. Second accurator 62B is oriented in the opposite direction and the orifice within second accurator 62B is sized to expand forward flow of liquid refrigerant R _L , thus preventing liquid refrigerant R _L from entering vapor volume 66. Second accurator 62B is also sized to allow any vapor refrigerant R _v present within

liquid volume 68 to enter vapor volume 66. Thus, first accurator 62A and second accurator 62B provide phase separation of refrigerant flowing in the first direction.

Second accurator 62B is oriented to permit reverse flow of vapor refrigerant Ry from vapor volume 66 to pass through second accurator 62A unrestricted. Second accurator 62B is also sized to permit any liquid refrigerant R _L present within vapor volume 66 to pass through second accurator 62A. First accurator 62A is oriented in the opposite direction and the orifice within first accurator 62A is sized to expand reverse flow of vapor refrigerant Ry from vapor volume 66 to liquid volume 68. First accurator 62A is also sized to prevent reverse flow of liquid refrigerant R _L from vapor volume 66 to liquid volume 68. Thus, first accurator 62A and second accurator 62B provide phase separation of refrigerant flowing in the second direction.

As such, in the evaporator mode, flow regulating device 62 acts as a phase separating device that permits vapor refrigerant Ry to enter vapor volume 66 from liquid volume 68, and prevents liquid refrigerant R _L from entering vapor volume 66 from liquid volume 68. Thus, refrigerant vessel 12 feeds liquid refrigerant R _L to liquid header 44 and vapor refrigerant Ry to vapor header 42.

Vapor refrigerant Ry also occupies vapor volume 66 by passing through holes 70 in vapor tube 50. Vapor refrigerant Ry originating from both vapor volume 66 and heat exchange channels 48 collects in vapor header 42 before exiting heat exchanger 20 under suction from compressor 16, whereby vapor refrigerant Ry is returned to compressor 16 to be pressurized and heated to repeat the vapor-compression cycle.

As described with respect to FIG. 2A, in a typical, conventional, single-pass, parallel flow heat exchanger without a refrigerant vessel of the present invention, second end B of vapor header 42 would be closed off such that vaporized refrigerant only enters the vapor header from the heat exchange circuits. Additionally, first end C of liquid header 44 would be directly connected to the two-phase discharge of expansion device 22. As such, the liquid header would fill with both liquid and vapor refrigerant, thus promoting the aforementioned phase mal-distribution and its adverse effects on the performance of the heat exchanger. Refrigerant vessel 12 of the present invention diminishes these effects by allowing only liquid refrigerant R _L to enter liquid header 44. The pressurization of liquid volume 68 and the action of flow regulating device 62 acts as a phase- separator that shunts vapor refrigerant Ry around heat exchange channels 48, thus, eliminating the flow of already-vaporized vapor refrigerant Ry from flowing through channels 48. Thus, more of the capacity of heat exchange channels 48 is used

for evaporating liquid refrigerant R _L into vapor refrigerant R _v , increasing the efficiency of heat exchanger 20.

In another embodiment of the invention, flow regulating device 62 is comprised of a series of valves and restriction devices that regulate flow of liquid and vapor through vapor tube 50. For example, when heat exchanger 20 functions as a condenser the valves are both closed to prevent exchange of any refrigerant between vapor volume 66 and liquid volume 68. When heat exchanger 20 functions as an evaporator and two-phase refrigerant enters liquid volume 68 through access tube 58, the valves are opened to permit vapor refrigerant to flow through a restriction device to enter tube 50 and enter vapor volume 66 through holes 70 in vapor tube 50, which prevents liquid from entering vapor volume 66.

FIG. 3 shows heat exchanger 20 of system 10 from FIG. 1 operating as a pump- down storage volume. As mentioned above, it is sometimes desirable to redistribute refrigerant within the vapor-compression circuit of system 10 such that maintenance or other activities can be performed on the various components of system 10. One method of performing this redistribution is to close valve 40 positioned in the vapor-compression circuit and to run compressor 16 to pump liquid refrigerant R _L into heat exchanger 20.

Upon initiation of a pump-down operation, service valve 40 is closed to prevent effluent flow of refrigerant from heat exchanger 20. Service valve 40 comprises and actively controlled valve that can be connected to controller 28. In another embodiment, service valve 40 comprises a passively controlled valve that is manually operated. Valve 40 is placed as close as practical to expansion device 22 for the embodiment shown.

Liquid refrigerant R _L , indicated by outlined arrows, is pumped into vapor header 42 from compressor 16 through line 25C. Liquid refrigerant R _L flows into vapor header 42, heat exchange channels 48 and liquid header 44. From liquid header 44, liquid refrigerant R _L flows into and fills liquid volume 68 and access tube 58. Service valve 40 prevents liquid refrigerant R _L from continuing into line 25B. Flow regulating device 62 prevents liquid refrigerant R _L from continuing into vapor volume 66 under similar operation as described with respect to FIG. 2A. With liquid refrigerant R _L prevented from leaving heat exchanger 24, liquid refrigerant R _L accumulates within heat exchange channels 48 and vapor header 42. Liquid refrigerant R _L also travels into vapor tube 50, where holes 70 permit liquid refrigerant R _L to enter vapor volume 66. Holes 70 comprise large diameter holes to prevent any phase changing of the refrigerant. Thus,

depending on the specific designed sizes, nearly the entireties of heat exchanger 20 and vessel 12 are filled with liquid refrigerant R _L .

Typically, heat exchanger 20 is only partially occupied with refrigerant during operation of system 10 in a heating or cooling mode. In particular, the heat exchange channels of both heat exchanger 20 and heat exchanger 24 are only partially filled with liquid refrigerant, with the rest occupied by vapor refrigerant. In a pump-down operation, most refrigerant within the heat pump system is condensed into a liquid, while a small amount of lower density vapor remains dispersed throughout the system. However, in typical parallel flow heat exchangers, including MCHX heat exchangers, there is a greater amount of liquid refrigerant present in the heat pump system than there is volume available in only one of the heat exchangers during pump-down operation.

System 10 utilizes space available within vessels 12 and 14 to store liquid refrigerant during a pump-down operation. For example, as shown in FIG. 2A, vapor header 42 and vapor volume 66 of heat exchanger 20 are typically void of liquid refrigerant R _L when functioning as a condenser. As shown in FIG. 2B, liquid volume 68 of heat exchanger 20 typically is only partially full when functioning as an evaporator. The volume of available space within vessels 12 and 14 is sized to meet or exceed the volume needed during a pump-down operation and depends on specific components used within system 10. For example, in one embodiment, the volume of empty space within heat exchanger 20 during operation of system 10 equals the volume of occupied space within heat exchanger 24 during operation of system 10, plus any additional occupied space within the plumping and components between the two heat exchangers, such as compressor 16. Thus, during a pump-down operation, the total volume of the vapor volume, the liquid volume, the liquid header, the vapor header and the heat exchange circuits of one heat exchanger and one refrigerant vessel is capable of holding the total volume of refrigerant necessary to operate system 10 when condensed into a liquid. As such, the volumes of vapor volume 66 and liquid volume 68 are greater than what would ordinarily be required to conduct liquid refrigerant R _L and vapor refrigerant Ry between line 25B and line 25C when heat exchanger 20 operates either as a condenser or evaporator.

FIG. 4 shows heat exchanger 74 incorporating refrigerant vessel 76 of the present invention. Heat exchanger 74 and refrigerant vessel 76 include similar components as heat exchangers 20 and 24 and refrigerant vessels 12 and 14 of FIGS. 2A and 2B, and are identified as such. Heat exchanger 74, however, illustrates different plumbing and valve

placement configurations for arrangement of features of the present invention. For example, in heat exchanger 74, vapor tube 50 is piped to connect liquid volume 68 and vapor volume 66 directly with line 25C, bypassing vapor header 42. Thus, the length of vapor tube 50 is increased to provide additional pump-down storage volume. Lengthening of vapor tube 50 and bypassing vapor header 42 may also assist in reducing flow mal-distribution effects. Flow regulating device 62 is positioned inside vapor tube 50 outside of vessel body 54. Thus, in conjunction with various pipe fittings, flow regulating device 62 can be accessed as needed without having to disassemble refrigerant vessel 76. Additionally in heat exchanger 74, stop valves 78A and 78B are positioned within vapor tube 50 on either side of flow regulating device 62. Thus, during maintenance or repair, heat exchanger 76 can continue to operate as a conventional heat exchanger while flow regulating device 62 is attended to. Also, expansion device 80 is positioned within liquid tube 52 to provide additional expansion of liquid refrigerant entering liquid header 44 from liquid volume 68. Additional expansion devices and stop valves can be included as needed for specific design needs.

As is known to those skilled in the art, the heat exchangers and refrigerant volumes of the present invention can be used in other types and configurations of heat exchangers. For example, refrigerant vessels of the present invention can be positioned between passes in multi-pass heat exchangers. For example, with respect to FIG. 4, a plurality of heat exchangers 76 could be connected in series such that line 25B of a first heat exchanger 76 could be connected to line 25C of a second heat exchanger 76. Also, vapor tube 50 and liquid tube 52 can be connected to vapor and liquid headers, respectively, that serve multi-circuit heat exchangers in which a plurality of heat exchange circuits connect the headers. Additionally, vapor header 42 and liquid header 44 may include multiple inlets and outlets depending on the number of passes and circuits being served. In other embodiments of the present invention, headers 42 and 44 may be connected with heat exchange circuits that are arranged horizontally, vertically, or at any angle in between, including combinations of angles. Refrigerant vessels of the present invention provide a flow- separation function for heat exchangers acting as evaporators, and provide a stop valve function for heat exchangers acting as condensers for a variety of heat exchanger configurations, including parallel flow heat exchangers. The vessels assist in reducing flow mal-distribution and phase mal-distribution. The refrigerant vessels also provide additional storage volume within the heat exchangers

such that pump-down operations may be performed when the heat exchangers are incorporated in vapor-compression systems such as heat pumps.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.