Heat Exchanger Apparatus

Abstract

Embodiments disclosed herein include a heat exchanger comprising a first heat exchanger and a second heat exchanger. The first heat exchanger receives a working fluid in a gaseous state and outputs the working fluid in liquid state. The second heat exchanger further sub cools the working fluid.

Description

BACKGROUND

The present disclosure pertains to heat exchangers. In one example embodiment, the present disclosure pertains to a sub-cooling heat exchanger, including systems and method of using the same.

Heat exchangers are systems used to transfer heat between a source fluid and a working fluid (e.g., where the fluids are liquids or gases). Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact, for example. One commonly used class of working fluids is refrigerants. Refrigerants are used in a direct expansion (DX) system to transfer energy from one environment to another, typically from inside a building to outside (or vice versa) commonly known as an “air conditioner” or “heat pump”. Some example refrigerants can carry 10 times more energy per kg than water, and 50 times more than air.

The present disclosure pertains to heat exchangers with improved heat transfer efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a heat exchanger apparatus according to an embodiment.

FIG. 1B illustrates a heat exchanger apparatus according to another embodiment.

FIG. 1C illustrates fluid flow in a heat exchanger according to an embodiment.

FIG. 2A illustrates another example heat exchanger according to an embodiment.

FIG. 2B illustrates yet another example heat exchanger according to an embodiment.

FIG. 2C illustrates fluid flow in a heat exchanger according to another embodiment.

FIG. 3 illustrates an example heat exchanger configuration according to another embodiment.

FIG. 4A illustrates an example system including a heat exchanger according to an embodiment.

FIG. 4B illustrates an example system including a heat exchanger according to an embodiment.

FIG. 5 illustrates another example heat exchanger according to another embodiment.

FIG. 6 illustrates a planar area of a heat exchanger according to an embodiment.

FIG. 7 illustrates example entropy curves for a heat exchanger according to an embodiment.

FIG. 8 illustrates a method according to an embodiment.

DETAILED DESCRIPTION

Described herein are techniques for heat exchangers. In the following description, for purposes of explanation, numerous examples and specific details are set forth in order to provide a thorough understanding of some embodiments. Various embodiments as defined by the claims may include some or all of the features in these examples alone or in combination with other features described below and may further include modifications and equivalents of the features and concepts described herein.

Embodiments of the present disclosure include a heat exchanger apparatus with improved heating efficiency. In one embodiment, a working fluid (e.g., a refrigerant) enters a first heat exchange and conveys energy to another fluid (a “system fluid”, e.g., air). After leaving the first heat exchanger, the working fluid is passed through a second heat exchanger, which further conveys energy to the system fluid. The second heat exchanger may be arranged such that the system fluid flows into the second heat exchanger before entering the first heat exchanger. In one example embodiment, the system fluid entering the heat exchanger may further remove heat energy from the working fluid in the second heat exchanger. This heat energy is picked up directly by the system fluid before it enters the first heat exchanger, thereby boosting the total heating performance of the unit.

FIG. 1A illustrates a heat exchanger apparatus according to an embodiment. Heat exchanger apparatus 100 comprises a first heat exchanger 101 and a second heat exchanger 102. A system fluid, such as air, flows into the second heat exchanger 102 and out of the first heat exchanger 101. Accordingly, the system fluid through the second heat exchanger 102 is upstream of the system fluid through the first heat exchanger 101. In some embodiments, the output system fluid is circulated back to the system fluid input (sometimes referred to as the “return” system fluid input). The first heat exchanger 101 is configured to receive a working fluid (e.g., refrigerant) on fluid terminal 110, which has a first temperature, Tw1. Example fluid terminals may include ends of pipes carrying liquids and gases as described in more detail below. Heat exchanger 101 outputs the working fluid on fluid terminal 111 at a second temperature, Tw2. When a system is configured to increase the temperature of the system fluid (e.g., from temperature T1 on the input side to a higher temperature T2 on the output side), the second temperature Tw2 of the working fluid is less than the first temperature Tw1 as heat is transferred from the working fluid to the system fluid as the system fluid flows through first heat exchanger 101.

As the temperature of the working fluid is reduced, certain embodiments may be arranged so that the working fluid changes state between terminal 110 and terminal 111 of the first heat exchanger 101. For example, the working fluid may be a gas when entering heat exchanger at terminal 110, and the energy transfer in heat exchanger 101 may cause the working fluid to change to a liquid at temperature Tw2 when output from terminal 111. Heat exchanger may be referred to as “subcooled” as it exits heat exchanger 101 at terminal 111, for example. The term subcooling (also called undercooling) is sometimes used when referring to a liquid existing at a temperature below its normal boiling point.

Features and advantages of the present disclosure include a heat exchanger configured to further subcool a subcooled output of a previous heat exchanger to improve the efficiency of the combined heat exchanger system. In this example, the working fluid may be coupled from terminal 111 of heat exchanger 101 to terminal 112 of second heat exchanger 102. Second heat exchanger 102 is configured to receive the working fluid in the liquid state at the second temperature Tw2 and output the working fluid in a liquid state at a third temperature Tw3 that is less than the second temperature Tw2, for example. The additional temperature drop of the working fluid corresponds to additional heat transfer from the working fluid to the system fluid. In this example, the system fluid is entering the system and encountering the already cooled working fluid. Accordingly, while the working fluid temperature in heat exchanger 102 may be lower than in heat exchanger 101, the system fluid entering the system is at its highest temperature relative to the path of the system fluid through the heat exchanger system 100, thus allowing the system fluid to further reduce the working fluid's temperature and “pre-heating” the system fluid. This results in improved efficiency of the heat exchanger system.

Advantageously, a first temperature difference between the first temperature Tw1 and the second temperature Tw2 is greater than a second temperature difference between the second temperature Tw2 and the third temperature Tw3. Accordingly, in some embodiments, a majority of the heat transfer from the working fluid to the system fluid occurs in the first heat exchanger 101. Therefore, a temperature of the system fluid increases as the system fluid flows through the second heat exchanger 102, and further increases (e.g., by a greater amount) as the system fluid flows through the first heat exchanger 101 such that a temperature increase of the system fluid from the first heat exchanger 101 is greater than a temperature increase of the system fluid from the second heat exchanger 102.

For example, the second and third temperatures Tw2 and Tw3 of the working fluid at the input and output of the second heat exchanger 102, respectively, are greater than a temperature of the system fluid when the system fluid enters the second heat exchanger 102. This arrangement allows the second heat exchanger 102 to convey more heat energy to the system fluid than the first heat exchanger 101 by itself, for example. Furthermore, in some embodiments, the temperature of the subcooled liquid working fluid at the output of the second heat exchanger 102 may be near in temperature to the input temperature of the system fluid. In some embodiments, a difference between working fluid temperature Tw2 at the input of the second heat exchanger 102 and the working fluid temperature Tw3 at the output of the second heat exchanger 102 is greater than a difference between the working fluid temperature Tw3 at the output of the second heat exchanger 102 and the temperature, T1, of the system fluid entering the second heat exchanger 102. For example, the second heat exchanger 102 may reduce the temperature of a refrigerant by 15 degrees Fahrenheit (F), while the output temperature of the refrigerant exiting the second heat exchanger 102 may be only 5 degrees F. higher than an input temperature T1 of the air entering the second heat exchanger 102.

FIG. 1B illustrates a heat exchanger apparatus according to another embodiment. In this example, working fluid flows into terminal 111, through heat exchanger 101 and out of terminal 110. Second heat exchanger 102 comprises an open terminal 113 (e.g., blocked so that no fluid can flow through terminal 113. Terminal 112 of heat exchanger 102 is coupled to terminal 111 of heat exchanger 101. This configuration may be used in, for example, a situation where the system fluid decreases from temperature T1 at the input of the heat exchanger system to temperature T2 at the output of the heat exchanger system (T2<T1; cooling). Accordingly, the temperature Tw2 of working fluid at terminal 111 may be greater than the temperature Tw1 at terminal 111 as heat is transferred from the system fluid to the working fluid. Advantageously, in this embodiment, second heat exchanger 102 acts as a charge compensator (aka, a “tank”). In some embodiments, working fluid in second heat exchanger 102, which may initially be in a liquid state, may change state to a gas (e.g., when exposed to a high pressure at terminal 111) and provide additional working fluid into the first heat exchanger and other components in the working fluid circuit (e.g., as described further below). Some thermal management systems use costly external tank circuits as part of the system. However, the techniques of the present disclosure advantageously allow a second heat exchanger 102 to act as a tank for the circuit, which may eliminate the need for an additional and separate tank component, for example.

FIG. 1C further illustrates a heat exchanger apparatus according to an embodiment. This figure illustrates that the first heat exchanger 101 may define a first physical area, P1, 150 (e.g., a rectangular plane). The second heat exchanger 102 may define second physical area, P2, 151 (e.g., a rectangular plane) in parallel with the first area and separated by a gap (g). The system fluid flows through the first and second heat exchangers 101-102 perpendicular (e.g., substantially orthogonal) to the first and second areas 150-151. For instance, the system fluid may flow into the second heat exchanger 102 across the second area 151 and out of the first heat exchanger 101 across the first area 150. In some embodiments areas 150-151 comprise a rectangular shaped region with rows of tubes carrying working fluid between opposite sides with heat transfer foils between the rows to improve heat transfer as a system fluid (e.g., air) flows across the rectangular shaped regions.

In this embodiment, working fluid flows into heat exchanger 101, between the heat exchangers (e.g., using a connecting pipe), and out of heat exchanger 102. More specifically, working fluid may flow into, and along a proximate edge of, heat exchanger 101 along first side 160. Heat exchanger 101 is configured to cause the working fluid to flow from the first side 160 (here, the top) of heat exchanger 101, along area P1150, and to a distal edge of heat exchanger 101 on opposite side 161. The working fluid exits heat exchanger 101 along the opposite side 161. The working fluid exiting heat exchanger 101 is coupled into, and along a proximate edge of, heat exchanger 102 along side 162. Heat exchanger 102 is configured to cause the working fluid to flow from side 162 (here, the bottom) of heat exchanger 102, along area P2151, and to a distal edge of heat exchanger 102 on side 163, which is opposite to side 162. Adjacent heat exchangers configured with fluid flowing in opposite directions as shown here is referred to as a counterflow configuration. Further examples of the features in FIGS. 1A-C are illustrated below.

FIG. 2A illustrates another example heat exchanger according to an embodiment. In this example, a heat exchanger includes a first heat exchanger 201 and a second heat exchanger 202 configured as illustrated in FIG. 1A with system fluid flowing into the second heat exchanger 202 at a first temperature T1 and out of the first heat exchanger 201 at a temperature T2 (e.g., where T2>T1). In this embodiment, first heat exchanger 201 comprises a first sub-heat exchanger 201a configured to receive the working fluid on terminal 210 at the first temperature Tw1 (e.g., in the gaseous state) and output the working fluid on terminal 220 at an intermediate temperature Tw1. A second sub-heat exchanger 201b is configured to receive the working fluid on terminal 221 from terminal 220 at the intermediate temperature Tw1 and output the working fluid (e.g., in a liquid state) on terminal 211 at the second temperature Tw2. Second sub-heat exchanger 201b may receive the working fluid in a gaseous state from the first sub-heat exchanger 201a and output the working fluid in a liquid state, for example. The system fluid may flow through the second sub-heat exchanger 201b before the first sub-heat exchanger 201a so that the temperature of the system fluid is higher passing through the first sub-heat exchanger 201a than it is when passing through the second sub-heat exchanger 201b.

As illustrated in examples below, the first sub-heat exchanger 201a may define the first area (mentioned above) and the second sub-heat exchanger 201b may define a third area, where the first area is configured in parallel with the third area. For example, the first area may be a first planar surface, the third area may be a third planar surface, and a second area defined by the second heat exchanger 202 may be a second planar surface as mentioned above. The first, second, and third planar surfaces may be substantially the same size in some embodiments, where the first planar surface is parallel to and offset from the third planar surface, for example. The working fluid may flow over the first and third planar surfaces in counterflow, and the working fluid flows over the second and third planar surfaces in counterflow. Accordingly, the working fluid transfers thermal energy with the first fluid across substantially all of the first, second, and third planar surfaces.

FIG. 2B illustrates yet another example heat exchanger according to an embodiment. This example shows heat exchanger 201 running in reverse, where system fluid input temperature T1 is greater than system fluid output temperature T2 (cooling the system fluid). As described in connection with FIG. 1B, second heat exchanger 202 may form a tank, where working fluid in the second heat exchanger 202 may transition from liquid into a gas and is absorbed by the working fluid circuit.

FIG. 2C illustrates fluid flow in a heat exchanger according to another embodiment. Similar to FIG. 1C, sub-heat exchangers 201a-b are configured in counterflow, and sub-heat exchanger 201b is configured in counterflow with second heat exchanger 202. For instance, working fluid flows into sub-heat exchanger 201a at temperature Tw1, between the sub-heat exchangers (e.g., using a connecting pipe), and out of sub-heat exchanger 201b (e.g., and into second heat exchanger 202). More specifically, working fluid may flow into, and along a proximate edge of, sub-heat exchanger 201a along first side 260. Sub-heat exchanger 201a is configured to cause the working fluid to flow from the first side 260 (here, the top) of sub-heat exchanger 201a, along area P1251a, and to a distal edge of sub-heat exchanger 201a on opposite side 261. The working fluid exits sub-heat exchanger 201a along the opposite side 261 at temperature Tw1. The working fluid exiting sub-heat exchanger 201a is coupled into, and along a proximate edge of, sub-heat exchanger 201b along side 262. Sub-heat exchanger 201b is configured to cause the working fluid to flow from side 262 (here, the bottom) of sub-heat exchanger 201b, across area P2251b, and to a distal edge of heat exchanger 201b on side 263, which is opposite to side 262. The output of heat exchanger 201 is then coupled to the input of heat exchanger 202 as described in FIG. 1C, where sub-heat exchanger 201b is configured in counterflow with second heat exchanger 202.

FIG. 3 illustrates an example heat exchanger configuration according to another embodiment. In some embodiments, heat exchangers may be configured to operate in multiple modes. In a first mode, working fluid flows through multiple heat exchangers in a first directions (e.g., heating mode), and in a second mode, working fluid flows through a portion of the heat exchangers while one heat exchanger acts as a tank. In this example, a heat exchanger 301 comprises terminals 310 and 311 and heat exchanger 302 comprises terminals 312 and 313. Terminals 311 and 312 are coupled together and further coupled to a terminal of a valve 321. Terminal 313 is coupled to a terminal of valve 322. A second terminal of valve 321 is coupled to a second terminal of valve 322 and further coupled to a terminal 320. Accordingly, when working fluid flows in a first direction 390 (e.g., in a heating mode), the working fluid passes through multiple heat exchangers 301 and 302 (e.g., including sub-heat exchangers in 301 in some embodiments). However, when working fluid flows in a second direction 391 (e.g., in a cooling mode), the working fluid passes through heat exchanger 301 (e.g., including sub-heat exchangers in 301 in some embodiments) and bypasses heat exchanger 302. In some embodiments, valves 321 and/or 322 may be passive (e.g., non-electrically activated) one-way values (aka, check valves) that are configured to only pass fluid in one direction and block fluid in the other direction, for example. In other embodiments, electrical valves may be used that are activated to control the flow as described above.

FIG. 4A illustrates an example system including a heat exchanger according to an embodiment. One example system using a heat exchanger of the present disclosure is a heat pump system. Heat pumps are used in many applications to provide temperature control to a space. A heat pump may perform this function by adding (or removing) heat to (or from) the space, and sourcing (or rejecting) heat from (or to) an area outside of the temperature controlled space. As illustrated in FIG. 4A, heat pumps may be composed of 5 elements: a compressor 413 for moving working fluid (refrigerant) through a circuit, a primary side heat exchanger 410 for exchanging heat with the controlled temperature space 452, a secondary side heat exchanger 411 for sourcing/sinking heat into a space outside of the temperature controlled space, a metering valve 415 which regulates the flow of refrigerant through the circuit, and a reversing valve 414 which changes the flow direction of the working fluid, enabling the circuit to add or extract heat to or from the temperature controlled space (e.g., for heating or cooling).

FIG. 4A illustrates a heating mode. During heating mode, heat is extracted from a heat source 450 and the heat pump transfers the heat to a controlled space 452. During the process of heating space 452, hot gaseous working fluid from the compressor enters the heat exchanger (HX) 410, and heat is imparted to a system fluid flowing into space 452 (e.g., air flowing into a room) as the working fluid changes phase from gas to a liquid. It may continue this process until all of the working fluid is in a liquid state and is sub-cooled as described herein.

As mentioned above, according to the presently disclosed heat exchanger, a subcooled liquid working fluid leaving one heat exchanger is passed through a second heat exchanger to further subcool the working fluid to near (and slightly above) the temperature of the system fluid. The second subcooling heat exchanger is arranged upstream in the airflow of heat exchanger 410. In such an arrangement, the cool return system fluid from the space can further remove heat energy from the liquid working fluid to within a few degrees of each other. This heat energy is picked up directly by the return system fluid before it enters the first heat exchanger (e.g., heat exchanger 101 in FIG. 1A), thereby boosting the total heating performance of the unit. Advantageously, the working fluid leaving the second heat exchanger (e.g., heat exchanger 102 in FIG. 1A) is greatly subcooled, such that it has more capacity to remove heat from the heat source 450 (e.g., once it passes through the metering valve and enters heat exchanger 411). Lastly, heat exchanger 411 may be advantageously sized appropriately to enable the extra heat extraction enabled by the improved heat exchanger apparatus 410, for example.

FIG. 4B illustrates an example system including a heat exchanger according to an embodiment. Here, reversing valve 414 changes the flow direction and the system is operating in cooling mode. In cooling mode, heat is extracted from the working fluid by heat sink 451. Cool working fluid is coupled to heat exchanger 410 to reduce the temperature of system fluid entering space 452 so that T2 is less than T1. Heat exchanger 410 may be configured as described in FIG. 1B or 3B, for example, where one heat exchanger acts as a tank for the circuit.

In particular, in heating mode (FIG. 4A), compressor 413 increases the pressure of gaseous working fluid. The hot, high pressure working fluid is coupled to the input of HX 410 (e.g., 290-300 psi at approximately 180 degrees F.). The output pressure of HX 410 remains high (e.g., 300 psi) but the output temperature drops just above temperature T1 due to the sub-cooling second heat exchanger configured as described above (e.g., within about 5 degrees F. in some embodiments). However, when the system switches to cooling mode, the pressure in HX 410 drops (e.g., from 300 psi to 100 psi). Previously stored working fluid in the second heat exchanger (e.g., 102) experiences a drop in pressure and converts from liquid to gas (e.g., “flashes off”) and the extra working fluid is absorbed by the working fluid circuit, thereby acting as a tank (or charge compensator) for the system without the need for an additional charge compensator (advantageously reducing system costs).

Accordingly, embodiments of the heat exchanger apparatus disclosed herein may increase the heating capacity of heat pump units without creating extra workload on the compressor and increase the coefficient of performance of the system because of this same effect. Some embodiments may also provide an inherent charge compensator, which may reduce system costs. It is to be understood that the present techniques may be applied to air source heat pumps as well as other heat exchange applications and would have the same effects on those systems. For example, in some embodiments, the heat source and sink are ground sourced heat pumps where ground loops are placed in the ground and the thermal properties of the ground are used as heat source and/or sink (e.g., at different times of year). Such a system may be an example of a heat pump to maintain an interior space of a house comfortable while using the ground as the outside space where heat is sourced or rejected. During heating mode, the ground loop is extracting heat from the ground and the heat pump is transferring the heat into the house. During cooling mode, the ground loop sinks heat to the ground and the heat pump transfers the heat out of the house. As mentioned above, embodiments of the heat exchanger apparatus described above may not be restricted to ground-source heat pumps.

FIG. 5 illustrates an example heat exchanger apparatus according to an embodiment. The present example illustrates a home heating application, but it will be evident to those skilled in the art that a wide range of other applications are possible. This example includes a primary heat exchanger 520 and secondary heat exchanger 521. Air flows from a low temperature input (e.g., return air from a house) at 502, through the secondary heat exchanger 521, through a gap between the heat exchangers, and through primary heat exchanger 520 to supply heated air to a house at 503. Hot refrigerant in a gas state enters the system at 501 at pipe terminal 550 and enters the primary heat exchanger through pipe terminal 551. Pipe terminal 551 is coupled to an internal pipe (not shown) running along a length of the edge of heat exchanger 520 to distribute the refrigerant along the length of the lower edge. The refrigerant flows upward through the primary heat exchanger (e.g., through tubes described above) toward a top edge and then loops back at 510 and flows downward through the primary heat exchanger 520 back toward the lower edge. The refrigerant gas condenses to a liquid and transfers heat to the air. The primary heat exchanger 520 may sub-cool the refrigerant, thus taking refrigerant temperature below gas-liquid state transition point. In this example, the sub-cooled refrigerant then moves through primary heat exchanger 520 output pipe 552, upward to a T-connect pipe 553, and then down at 505 and into the secondary heat exchanger pipe 554. Pipe 554 is coupled to an internal pipe 555 running along the lower edge of secondary heat exchanger 521. Refrigerant enters the internal pipe 555 on the lower edge and flows upward (e.g., through tubes described above) as illustrated at 506. Accordingly, refrigerant in the primary heat exchanger flows upward, then downward, and into the upward in secondary heat exchanger all in counterflow. Sub-cooled liquid refrigerant travels upward at 506 through the secondary heat exchanger, further subcooling the liquid and heating the input air from the house. The secondary heat exchanger 521 further sub-cools the refrigerant, which enters another internal chamber along the upper edge of secondary heat exchanger 521 and exits the secondary heat exchanger at pipe terminal 557.

In this example, a check valve 558 coupled between the pipe terminal 557 and a pipe terminal 561 of the composite system allows refrigerant to flow from terminal 557 and out of terminal 561 at 507 during heating mode and blocks flow in the reverse direction during cooling mode. A second check valve 559 coupled between the pipe terminal of the composite system 561 and pipe terminals 552 of the primary heat exchanger 520 and terminal 554 of the secondary heat exchanger 521 allows refrigerant to flow into terminal 561 to terminal 552 during cooling mode. Check valve 559 further configures the secondary heat exchanger as a tank during cooling mode. Accordingly, refrigerant flows through the primary and secondary heat exchangers when in heating mode, while also enabling a reverse cooling mode, for example, where the refrigerant flows in the opposite direction through the primary heat exchanger and bypasses the secondary heat exchanger.

For illustrative purposes, the following are some example temperatures that may be seen in the system: input air from the house=68 F, temperature between the heat exchangers=70 F, output air to the house=95 F, temperature of refrigerant input to primary heat exchanger=160 F (gaseous state), temperature of refrigerant at intermediate pipe between primary and second heat exchangers=88 F (liquid state), temperature of output refrigerant from secondary heat exchanger=70 F (greater than air in).

FIG. 6 illustrates a planar area of an example heat exchanger 600 according to an embodiment. In one embodiment, a heat exchanger may comprise multiple tubes 602 for passage of refrigerant flow on the interior of the exchanger. The tubes may be coupled to aluminum or copper fin material 603, which are effectively cooled or heated by the refrigerant flowing in the tubes. Working fluid (here, refrigerant) enters a main input tube 601 and is passed through the tubes. Heat energy is exchanged between the tubes and fins 603. The system fluid (here, air) flows over the fins 603 and picks up heat or rejects heat as it passes over the fins. This system fluid flow is then recirculated to and from the temperature controlled space in order to add or remove heat, depending on the mode of operation. A planar area 604 may be defined over the input to the heat exchanger defined by ends (or openings) of the passages 602 and fins 603. A second area (not shown) may be defined by opposite ends (or openings) of passages 602 and fins 603 through which the air flows out of the heat exchanger. Accordingly, in this example, planar areas on opposite sides of the ends of the passages 602 and fins 603 form a rectangular volume, where the system fluid (e.g., air) enters the volume through planar area 604 and exits the volume on the opposite side, for example.

Furthermore, in this example the refrigerant in the tubes 602 is changing phase as it rejects or absorbs heat from the air. For a cooling operation, the refrigerant is evaporating from a liquid to a gas as heat is transferred from the air to the refrigerant. For heating, the refrigerant is condensing from a gas to a liquid as heat is transferred from the refrigerant to the air, thereby reducing the energy in the refrigerant. For heat transfer to take place, a temperature difference is present, as described in the following equation.

Q=U*A*dT, where

• • Q=heat−(Watts or Btu/hr)
  • U=heat transfer coefficient
  • A=Surface area of the exchanger
  • dT=Temperature difference between the refrigerant and the air.

Thermodynamic principles determine operating temperatures and efficiencies achievable by heat pumps and air conditioners. Operating temperatures may be controlled by operating limits of the compressor. Efficiency of the system is affected by the temperature differences achievable by the heat exchangers as they determine compressor operating pressures, for example.

FIG. 7 illustrates example entropy curves for a heat exchanger according to an embodiment. As shown in the diagram, various arrangements as described above can increase sub-cooling of the liquid refrigerant. As illustrated at 702, an additionally subcooled liquid has more heat extraction capacity.

FIG. 8 illustrates a method according to an embodiment. At 801, a working fluid is received in a first heat exchanger at a first temperature in a gaseous state. At 802, the working fluid is output in a liquid state at a second temperature less than the first temperature. At 803, the working fluid is received in a second heat exchanger in the liquid state at the second temperature. At 804, the working fluid is output in the liquid state at a third temperature. The third temperature may be less than the second temperature and near an input system fluid temperature, for example. In one embodiment, the first heat exchanger defines a first area and the second heat exchanger defines a second area, wherein the first area is configured in parallel with the second area. In one embodiment, a first fluid flows into the second heat exchanger across the second area and out of the first heat exchanger across the first area. At 805, the flow of the working fluid may be reversed in the first heat exchanger and the second heat exchanger is bypassed.

Further Example Embodiments

Each of the following non-limiting features in the following examples may stand on its own or may be combined in various permutations or combinations with one or more of the other features in the examples below. In various embodiments, the present disclosure may be implemented as a system, method, or apparatus.

In one embodiment, the present disclosure includes a heat exchanger apparatus comprising: a first heat exchanger configured to receive a working fluid at a first temperature in a gaseous state and output the working fluid in a liquid state at a second temperature, wherein the second temperature is less than the first temperature; a second heat exchanger configured to receive the working fluid in the liquid state at the second temperature and output the working fluid in the liquid state at a third temperature less than the second temperature, wherein the first heat exchanger defines a first area and the second heat exchanger defines a second area, wherein the first area is configured in parallel with the second area, and wherein a first fluid flows into the second heat exchanger across the second area and out of the first heat exchanger across the first area.

In another embodiment, the present disclosure includes a method comprising: receiving a working fluid in a first heat exchanger at a first temperature in a gaseous state and outputting the working fluid in a liquid state at a second temperature, wherein the second temperature is less than the first temperature; receiving the working fluid in a second heat exchanger in the liquid state at the second temperature and outputting the working fluid in the liquid state at a third temperature less than the second temperature, wherein the first heat exchanger defines a first area and the second heat exchanger defines a second area, wherein the first area is configured in parallel with the second area, and wherein a first fluid flows into the second heat exchanger across the second area and out of the first heat exchanger across the first area.

In one embodiment, the working fluid in the liquid state at the second temperature received by the second heat exchanger is subcooled and wherein the working fluid in the liquid state at the third temperature is further subcooled.

In one embodiment, the third temperature of the working fluid is approximately equal to a fourth temperature of the first fluid flowing into the second heat exchanger.

In one embodiment, a first difference between the second temperature of the working fluid and the third temperature of the working fluid is greater than a second difference between the third temperature of the working fluid and a fourth temperature of the first fluid flowing into the second heat exchanger.

In one embodiment, a first temperature difference between the first temperature and the second temperature is greater than a second temperature difference between the second temperature and the third temperature.

In one embodiment, a temperature of the first fluid increases as the first fluid flows through the first heat exchanger and further increases as the first fluid flows through the second heat exchanger, wherein a temperature increase of the first fluid from the first heat exchanger is greater than a temperature increase of the first fluid from the second heat exchanger.

In one embodiment, the first fluid is air.

In one embodiment, the working fluid is refrigerant.

In one embodiment, the working fluid in the first heat exchanger is configured in counterflow with the working fluid in the second heat exchanger.

In one embodiment, the first heat exchanger defines a first planar surface and the second heat exchanger defines a second planar surface substantially a same size as the first planar surface, wherein the first planar surface is parallel to and offset from the second planar surface, and wherein the working fluid flows over the first and second planar surfaces, in counterflow, to transfer thermal energy with the first fluid across substantially all of the first and second planar surfaces.

In one embodiment, the first area is approximately a same size as the second area.

In one embodiment, the first area is a first planar surface and the second area is a second planar surface.

In one embodiment, the first heat exchanger comprises: a first sub-heat exchanger configured to receive the working fluid at the first temperature in the gaseous state and output the working fluid at an intermediate temperature; and a second sub-heat exchanger configured to receive the working fluid at the intermediate temperature and output the working fluid in the liquid state at the second temperature.

In one embodiment, the second sub-heat exchanger receives the working fluid in a gaseous state and outputs the working fluid in a liquid state.

In one embodiment, the first fluid flows into the second sub-heat exchanger prior to flowing into the first sub-heat exchanger.

In one embodiment, the first sub-heat exchanger defines the first area and the second sub-heat exchanger defines a third area, wherein the first area is configured in parallel with the third area.

In one embodiment, the first area is a first planar surface, the second area is a second planar surface, and the third area is a third planar surface substantially a same size as the first and second planar surfaces, wherein the first planar surface is parallel to and offset from the third planar surface, and wherein the working fluid flows over the first and third planar surfaces in counterflow, and wherein the working fluid flows over the second and third planar surfaces in counterflow, and wherein the working fluid transfers thermal energy with the first fluid across substantially all of the first, second, and third planar surfaces.

In another embodiment, the present disclosure includes a heat exchanger apparatus comprising: a first heat exchanger configured to receive a refrigerant at a first temperature and output the refrigerant at a second temperature less than the first temperature; and a second heat exchanger configured to receive the refrigerant at the second temperature and output the refrigerant at a third temperature less than the second temperature, wherein a gas flows into the second heat exchanger and out of the first heat exchanger, wherein a first temperature difference between the first temperature and the second temperature is greater than a second temperature difference between the second temperature and the third temperature, and wherein a temperature of the gas increases as the gas flows through the first heat exchanger and further increases as the gas flows through the second heat exchanger, wherein a temperature increase of the gas from the first heat exchanger is greater than a temperature increase of the gas from the second heat exchanger.

In one embodiment, the gas is air.

In one embodiment, the refrigerant is in a gaseous state at the first temperature and the refrigerant is in a liquid state at the second temperature.

In one embodiment, the second and third temperatures are greater than a temperature of the gas when the gas enters the second heat exchanger.

In one embodiment, first heat exchanger and the second heat exchanger are arranged in counterflow with the gas.

In one embodiment, the first heat exchanger defines a rectangular space arranged along a first plane; the second heat exchanger defines a rectangular space arranged along a second plane in parallel with the first plane and separated by a gap; and the gas flows through the first and second heat exchangers perpendicular to the first and second planes.

In one embodiment, the present disclosure includes a temperature control system comprising a compressor, a first heat exchanger, and a second heat exchanger. The compressor couples working fluid to the first and second heat exchangers. The first heat exchanger is coupled to a heat source or heat sink. The second heat exchanger comprises a subcooling heat exchanger as described herein. The second heat exchanger may act as a tank when the system switches from heating to cooling mode.

The above description illustrates various embodiments of the present disclosure along with examples of how aspects of the particular embodiments may be implemented. The above examples should not be deemed to be the only embodiments, and are presented to illustrate the flexibility and advantages of the particular embodiments as defined by the following claims. Based on the above disclosure and the following claims, other arrangements, embodiments, implementations and equivalents may be employed without departing from the scope of the present disclosure as defined by the claims.

Claims

1. A heat exchanger apparatus comprising: a first heat exchanger configured to receive a working fluid at a first temperature in a gaseous state and output the working fluid in a liquid state at a second temperature, wherein the second temperature is less than the first temperature; anda second heat exchanger configured to receive the working fluid in the liquid state at the second temperature and output the working fluid in the liquid state at a third temperature less than the second temperature,wherein the first heat exchanger defines a first area and the second heat exchanger defines a second area, wherein the first area is configured in parallel with the second area, andwherein a first fluid flows into the second heat exchanger across the second area and out of the first heat exchanger across the first area.

2. The heat exchanger apparatus of claim 1, wherein the working fluid in the liquid state at the second temperature received by the second heat exchanger is subcooled and wherein the working fluid in the liquid state at the third temperature is further subcooled.

3. The heat exchanger apparatus of claim 1, wherein the third temperature of the working fluid is approximately equal to a fourth temperature of the first fluid flowing into the second heat exchanger.

4. The heat exchanger apparatus of claim 1, wherein a first difference between the second temperature of the working fluid and the third temperature of the working fluid is greater than a second difference between the third temperature of the working fluid and a fourth temperature of the first fluid flowing into the second heat exchanger.

5. The heat exchanger apparatus of claim 1, wherein a first temperature difference between the first temperature and the second temperature is greater than a second temperature difference between the second temperature and the third temperature.

6. The heat exchanger apparatus of claim 1, wherein a temperature of the first fluid increases as the first fluid flows through the first heat exchanger and further increases as the first fluid flows through the second heat exchanger, wherein a temperature increase of the first fluid from the first heat exchanger is greater than a temperature increase of the first fluid from the second heat exchanger.

7. The heat exchanger apparatus of claim 1, wherein the first fluid is air.

8. The heat exchanger apparatus of claim 1, wherein the working fluid is refrigerant.

9. The heat exchanger apparatus of claim 1, wherein the working fluid in the first heat exchanger is configured in counterflow with the working fluid in the second heat exchanger.

10. The heat exchanger apparatus of claim 1, wherein the first heat exchanger defines a first planar surface and the second heat exchanger defines a second planar surface substantially a same size as the first planar surface, wherein the first planar surface is parallel to and offset from the second planar surface, and wherein the working fluid flows over the first and second planar surfaces, in counterflow, to transfer thermal energy with the first fluid across substantially all of the first and second planar surfaces.

11. The heat exchanger apparatus of claim 1, wherein the first area is approximately a same size as the second area.

12. The heat exchanger apparatus of claim 1, wherein the first area is a first planar surface and the second area is a second planar surface.

13. The heat exchanger apparatus of claim 1, wherein the first heat exchanger comprises: a first sub-heat exchanger configured to receive the working fluid at the first temperature in the gaseous state and output the working fluid at an intermediate temperature; anda second sub-heat exchanger configured to receive the working fluid at the intermediate temperature and output the working fluid in the liquid state at the second temperature.

14. The heat exchanger apparatus of claim 13, wherein the second sub-heat exchanger receives the working fluid in a gaseous state and outputs the working fluid in a liquid state.

15. The heat exchanger apparatus of claim 14, wherein the first fluid flows into the second sub-heat exchanger prior to flowing into the first sub-heat exchanger.

16. The heat exchanger apparatus of claim 13, wherein the first sub-heat exchanger defines the first area and the second sub-heat exchanger defines a third area, wherein the first area is configured in parallel with the third area.

17. The heat exchanger apparatus of claim 16, wherein the first area is a first planar surface, the second area is a second planar surface, and the third area is a third planar surface substantially a same size as the first and second planar surfaces, wherein the first planar surface is parallel to and offset from the third planar surface, and wherein the working fluid flows over the first and third planar surfaces in counterflow, and wherein the working fluid flows over the second and third planar surfaces in counterflow, and wherein the working fluid transfers thermal energy with the first fluid across substantially all of the first, second, and third planar surfaces.

18. A method comprising: receiving a working fluid in a first heat exchanger at a first temperature in a gaseous state and outputting the working fluid in a liquid state at a second temperature, wherein the second temperature is less than the first temperature; andreceiving the working fluid in a second heat exchanger in the liquid state at the second temperature and outputting the working fluid in the liquid state at a third temperature less than the second temperature,wherein the first heat exchanger defines a first area and the second heat exchanger defines a second area, wherein the first area is configured in parallel with the second area, andwherein a first fluid flows into the second heat exchanger across the second area and out of the first heat exchanger across the first area.

19. A heat exchanger apparatus comprising: a first heat exchanger configured to receive a refrigerant at a first temperature and output the refrigerant at a second temperature less than the first temperature; anda second heat exchanger configured to receive the refrigerant at the second temperature and output the refrigerant at a third temperature less than the second temperature,wherein a gas flows into the second heat exchanger and out of the first heat exchanger, wherein a first temperature difference between the first temperature and the second temperature is greater than a second temperature difference between the second temperature and the third temperature, andand wherein a temperature of the gas increases as the gas flows through the first heat exchanger and further increases as the gas flows through the second heat exchanger, wherein a temperature increase of the gas from the first heat exchanger is greater than a temperature increase of the gas from the second heat exchanger.

20. The heat exchanger apparatus of claim 19, wherein the gas is air.

21. The heat exchanger apparatus of claim 19, wherein the refrigerant is in a gaseous state at the first temperature and the refrigerant is in a liquid state at the second temperature.

22. The heat exchanger apparatus of claim 19, wherein the second and third temperatures are greater than a temperature of the gas when the gas enters the second heat exchanger.

23. The heat exchanger apparatus of claim 19, wherein first heat exchanger and the second heat exchanger are arranged in counterflow with the gas.

24. The heat exchanger apparatus of claim 19, wherein: the first heat exchanger defines a rectangular space arranged along a first plane;the second heat exchanger defines a rectangular space arranged along a second plane in parallel with the first plane and separated by a gap; andthe gas flows through the first and second heat exchangers perpendicular to the first and second planes.