HEAT EXCHANGER AND BRAYTON CYCLE SYSTEM BASED ON SOLUTION TO PINCH POINT IN THERMODYNAMIC CYCLE

Abstract

A heat exchanger based on solution to pinch point in a thermodynamic cycle includes a heat exchange core and a cover plate. The heat exchange core is sealed by the cover plate. Through coordinated structure of first and second flow channels and branch flow channels on alternately stacked cold side and hot side heat exchange plates, the heat exchanger of the present application improves heat exchange efficiency and avoids the adverse effects caused by pinch points. A Brayton cycle system including the heat exchanger is also provided.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of International Application No. PCT/CN2024/124127, filed on Oct. 11, 2024, which claims priority to Chinese Patent Application No. 202311814242.X, filed on Dec. 27, 2023. All of the aforementioned applications are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present application relates to the technical field of thermodynamic cycles, and in particular, to a heat exchanger and a Brayton cycle system based on a solution to a pinch point in a thermodynamic cycle.

BACKGROUND

In the thermodynamic cycle system, recuperators and coolers are key components for heat transfer. The recuperator recovers a portion of the high-grade heat from the turbine exhaust to preheat the working fluid. The incorporating regeneration raises the temperature of the working fluid entering the heat source, reduces irreversible heat absorption losses within the heat source, and improves the overall thermal efficiency of the cycle. The cooler functions primarily as a cold sink, enabling thermal-to-mechanical energy conversion and supplying low-temperature working fluid to the compressor. However, in existing thermodynamic systems, pinch phenomena may occur within heat exchangers such as recuperators and coolers. A pinch point refers to the location within a heat exchanger where the temperature difference between the hot and cold fluids reaches a minimum. Due to variations in the thermophysical properties of the working fluid, this minimum temperature difference may appear in the middle section of the heat exchanger rather than at the cold or hot end. When the pinch point arises in the central region of the heat exchanger, it can result in increased exchanger size, degraded heat transfer performance, and overall system inefficiency. This problem, in which the occurrence of a minimum temperature difference between the hot and cold fluids in the middle of the heat exchanger results in degraded heat transfer, is referred to as the pinch point problem. When heat exchangers including recuperators and coolers experience a pinch point problem, it can cause deterioration in heat transfer on both the hot and cold sides of the heat exchanger, a reduction in heat exchange efficiency, and localized overheating, which may result in excessive thermal stress on the heat exchanger and adversely affect the operation of the thermodynamic cycle system.

SUMMARY

The main objective of the present application is to provide a heat exchanger and a Brayton cycle system based on solution to pinch point in a thermodynamic cycle, so as to solve the pinch point problem that frequently occurs in a heat exchange device in the prior art.

In order to achieve the above purpose, the present application provides the following technical solutions. A heat exchanger, based on a solution to a pinch point in a thermodynamic cycle, which includes:

• • a heat exchange core, where the heat exchange core includes a plurality of cold side heat exchange plates and a plurality of hot side heat exchange plates stacked alternately; a first surface of each cold side heat exchange plate defines a plurality of first flow channels by first partitions; a second surface, which faces the same direction as the first surface, of each hot side heat exchange plate defines a plurality of second flow channels by second partitions; the cold side heat exchange plates and/or the hot side heat exchange plates further include branch flow channels; the branch flow channels are disposed along flow paths of all the first flow channels and/or all the second flow channels, and are in fluid communication with all the first flow channels and/or all the second flow channels, to converge or split flows within the cold side heat exchange plates and/or the hot side heat exchange plates; and
  • a cover plate, configured to seal the heat exchange core.

In an embodiment, the heat exchanger further includes a heat exchange interface, the heat exchange interface includes a cold side inlet, a cold side outlet, a hot side inlet, a hot side outlet and a branch port which are arranged on a side face of the heat exchange core, the cold side inlet and the cold side outlet are respectively connected to two ends of the second heat channels, the hot side inlet and hot side outlet are respectively connected to two ends of the second flow channels, the cold side inlet and the hot side inlet are respectively located on two opposite sides of the heat exchange core, the cold side outlet and the hot side outlet are respectively located on two opposite sides of the heat exchange core, and the branch port is connected to one end of the branch flow channels.

In an embodiment, the branch ports are provided in pairs, and the branch flow channels transversely penetrate through all the first flow channels and/or all the second flow channels, with two ends of the branch flow channels are connected to respective branch ports.

In an embodiment, each branch port is provided with a control valve to regulate flow entering the branch flow channel.

In an embodiment, a plurality of the branch flow channels are arranged at preset intervals on each cold side heat exchange plate and/or each hot side heat exchange plate.

In an embodiment, the partitions are a plurality of elongated grid plates arranged in parallel, and all the first flow channels and/or all the second flow channels are formed as continuous linear, zigzag, or meandering flow channels through the partitions.

In an embodiment, the partitions are a plurality of regularly distributed fins, and all the first flow channels and/or all the second flow channels are formed as aligned and interconnected non-continuous flow channels through the partitions.

In another aspect, the present application further provides a Brayton cycle system, where the Brayton cycle system includes a heat source, a thermoelectric conversion unit, a recuperating unit, a cooling unit, and a compression unit. The heat source, the thermoelectric conversion unit, the recuperating unit, the cooling unit, and the compression unit are in communication sequentially. The recuperating unit and the cooling unit each include the heat exchanger according to any one of the foregoing.

In an embodiment, the compression unit includes a main compressor and at least one re-compressor, an input end of the main compressor is connected to a hot side outlet of the cooling unit, an input end of the re-compressor is connected to a hot side outlet of the recuperating unit, an output end of the main compressor is connected to a cold side inlet of the recuperating unit, and an output end of the re-compressor is connected to a branch port of the recuperating unit.

In an embodiment, the hot side outlet of the cooling unit and a cold side outlet of the recuperating unit each are provided with a temperature monitoring unit, the Brayton cycle system further includes a measurement and control unit, the measurement and control unit is electrically connected to the control valve on each branch port and the temperature monitoring unit, and is configured to monitor the temperature at the hot side outlet of the cooling unit and the temperature at the cold side outlet of recuperating unit, and regulate a flow rate of a working fluid inside the cooling unit and the recuperating unit.

In an embodiment, a working fluid of the Brayton cycle system is supercritical carbon dioxide, a pressure at the cold side inlet of the recuperating unit is 12 MPa to 25 MPa, the pressure at the hot side inlet of the recuperating unit is 7.38 MPa, and a temperature at the cold side inlet of the recuperating unit is greater than 50° C.

The heat exchanger of the present application includes a heat exchange core and a cover plate, where the cover plate is configured to seal the heat exchange core. The heat exchange core is formed by alternately stacked cold side heat exchange plates and hot side heat exchange plates. A plurality of first flow channels are formed on a first surface of each cold side heat exchange plate by first partitions, and a plurality of second flow channels are formed on a second surface of each hot side heat exchange plate, facing the same direction as the first surface, by second partitions. In this way, the first flow channels and the second flow channels are separate from each other but enable heat exchange via thermal conduction through the cold side and hot side heat exchange plates, forming the core structure of the heat exchanger. Further, the present application provides that branch flow channels are formed on the cold side heat exchange plates and/or the hot side heat exchange plates (i.e., at least one of the two types of plates is provided with branch flow channels), such that the branch flow channels are in communication with all the first flow channels and/or all the second flow channels. These branch flow channels serve as inlets for external working fluid or outlets for internal working fluid on the heat exchange core, thereby enabling regulation of the flow rate of the working fluid within the heat exchanger. Additionally, working fluids with different thermal energies may be mixed through the branch flow channels to achieve efficient heat exchange inside the heat exchanger. This configuration avoids problems such as degraded heat transfer on the hot and cold sides due to excessively small temperature differences between the cold side and hot side heat exchange plates or the occurrence of a pinch point within the heat exchanger, which may otherwise lead to excessive localized temperature and thermal stress. As a result, the heat exchange efficiency of the heat exchanger can be directly and effectively improved through a self-regulating mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a simplified Brayton cycle system.

FIG. 2 shows the parameter variations along the flow path on the hot and cold sides of a recuperating unit under typical operating conditions when a pinch point occurs.

FIG. 3 is a schematic diagram illustrating the overall structure of a heat exchanger according to an embodiment of the present application.

FIG. 4 is an exploded schematic view of the heat exchange core of the heat exchanger according to an embodiment of the present application.

FIG. 5 is an enlarged schematic view of a portion A in FIG. 4.

FIG. 6 is a schematic diagram illustrating an embodiment of the structure of the first flow channels and/or second flow channels of the heat exchanger according to the present application.

FIG. 7 is another schematic diagram illustrating an embodiment of the structure of the first flow channels and/or second flow channels of the heat exchanger.

FIG. 8 is another schematic diagram illustrating an embodiment of the structure of the first flow channels and/or second flow channels of the heat exchanger.

FIG. 9 is a schematic diagram illustrating the logical connections of a Brayton cycle system according to an embodiment of the present application.

FIG. 10 is another schematic diagram illustrating the logical connections of a Brayton cycle system according to an embodiment of the present application.

FIG. 11A shows the temperature and specific heat at constant pressure of the working fluid on the hot and cold sides along the flow path for the first cold side pressures in a typical recuperating unit.

FIG. 11B shows the temperature and specific heat at constant pressure of the working fluid on the hot and cold sides along the flow path for the second cold side pressures in a typical recuperating unit.

FIG. 11C shows the temperature and specific heat at constant pressure of the working fluid on the hot and cold sides along the flow path for the third cold side pressures in a typical recuperating unit.

FIG. 11D shows the temperature and specific heat at constant pressure of the working fluid on the hot and cold sides along the flow path for the fourth cold side pressures in a typical recuperating unit.

FIG. 12A shows the temperature and specific heat at constant pressure of the working fluid on the hot and cold sides along the flow path for the first cold side inlet temperatures in the typical recuperating unit.

FIG. 12B shows the temperature and specific heat at constant pressure of the working fluid on the hot and cold sides along the flow path for the second cold side inlet temperatures in the typical recuperating unit.

FIG. 12C shows the temperature and specific heat at constant pressure of the working fluid on the hot and cold sides along the flow path for the third cold side inlet temperatures in the typical recuperating unit.

FIG. 12D shows the temperature and specific heat at constant pressure of the working fluid on the hot and cold sides along the flow path for the fourth cold side inlet temperatures in the typical recuperating unit.

FIG. 13A shows the parameters of the working fluid along the flow path on the hot and cold sides for the first cold side flow rate in a typical recuperating unit.

FIG. 13B shows the parameters of the working fluid along the flow path on the hot and cold sides for the second cold side flow rate in a typical recuperating unit.

FIG. 14 shows data of parameter variations along the flow path in a high-temperature recuperation section and a low-temperature recuperation section of the recuperating unit in the Brayton cycle system according to the present application.

Implementations, functional features, and advantages of the present disclosure will be further described with reference to the accompanying drawings in combination with the embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The technical solutions of the embodiments of the present application will be clearly and fully described below with reference to the accompanying drawings in the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present application.

The terms “first,” “second,” and “third” in the present application are used solely for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly indicating the quantity of the features referred to. Accordingly, features designated as “first,” “second,” or “third” may explicitly or implicitly include at least one such feature. As used herein, the term “plurality” means two or more, such as two, three, etc., unless otherwise specifically defined. All directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of the present application are intended solely to describe the relative positional relationships, movement conditions, and the like between components in a specific posture (such as that shown in the accompanying drawings). If the specific posture is changed, the corresponding directional indications shall be changed accordingly. In addition, the terms “comprise” or “include” and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus that comprises a series of steps or elements is not limited to only those steps or elements expressly listed but may optionally include other steps or elements not listed, or may optionally include additional steps or elements inherent to such process, method, product, or apparatus.

As used herein, the term “embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present application. The appearances of the phrase “in one embodiment” or similar expressions in various places throughout the specification are not necessarily all referring to the same embodiment, nor are they mutually exclusive alternative embodiments. It is explicitly and implicitly understood by those skilled in the art that the described embodiments can be combined with one another.

Thermal energy power generation typically utilizes water steam as the heat transfer working fluid, whereby water is heated and pressurized, and thermal energy is converted into mechanical energy via a turbine, which is then converted into electrical energy by a generator. In the current field of thermal power generation, supercritical carbon dioxide (sCO₂) has been widely adopted as the working fluid due to its advantages such as low critical temperature and pressure, liquid-like density, gas-like fluidity, and high heat transfer efficiency. Compared with conventional gaseous or steam-based working fluids, sCO₂ offers greater potential for application and research owing to these superior properties. At present, supercritical carbon dioxide is commonly used as the working fluid in Brayton cycle systems for thermodynamic power generation. FIG. 1 illustrates a schematic diagram of a simplified Brayton cycle system. A Brayton cycle system generally comprises, in sequence, a heat source, a turbine, a recuperating unit, a cooler, and a compressor connected in a closed loop. Typically, the turbine is coupled to a generator to convert mechanical energy into electrical energy, while the compressor is usually driven by a motor to compress the working fluid. The recuperating unit is used to recover part of the high-quality heat from the exhaust gas at the turbine outlet to preheat the working fluid. By incorporating a recuperative process, the temperature of the working fluid entering the heat source can be increased, thereby reducing the irreversible heat absorption loss within the heat source and improving the thermal efficiency of the cycle. The primary function of the cooler is to act as a cold source in the cycle to enable thermal-to-mechanical energy conversion and to provide low-temperature working fluid for the compressor. Leveraging the thermophysical property variations of supercritical carbon dioxide near its critical point, the cooler contributes to reducing compression power consumption and enhancing the overall cycle efficiency.

For example, in a Brayton cycle system, the heat exchanger such as the recuperating unit and the cooler inevitably leads to the pinch point. The pinch point refers to the location where the minimum temperature difference between the hot and cold fluids within the heat exchanger does not occur at the ends of the exchanger but at some points inside the exchanger. This can potentially lead to a deterioration in heat exchange efficiency or increase the complexity of the heat exchanger design. Therefore, preventing the occurrence of pinch points in heat exchangers such as recuperating units and coolers is of significant importance in improving efficiency and ensuring safety in various thermal power generation systems, including but not limited to those utilizing supercritical carbon dioxide as the working fluid in a Brayton cycle.

It should be noted that some parts of the description in the present application are provided for ease of understanding, and the explanation of the heat exchanger in the following sections will also be illustrated using the example of a Brayton cycle system utilizing supercritical carbon dioxide as the working fluid. However, this does not limit the application environment of the heat exchanger provided in the present application. Those skilled in the art should understand that devices with the same or similar structure to the heat exchanger in the present application, used to solve the pinch point problem in other thermal power generation systems, are also included within the scope of protection of the present application.

The occurrence of the pinch point in heat exchange devices is due to a significant change in the heat capacity flow rate (i.e., the product of mass flow rate and specific heat at constant pressure, mCp) of the two fluids involved in the heat exchange within the heat exchanger. This could occur, for example, when phase changes during the heat exchange process cause the specific heat at constant pressure to become infinite, or when changes in material properties cause the temperature curve to no longer approximate a straight line, resulting in the minimum temperature difference occurring within the heat exchanger. FIG. 2 shows the changes in the parameters along the hot and cold sides of the heat exchanger when the pinch point phenomenon occurs, using a recuperating unit as an example under typical parameter conditions. It can be seen from FIG. 2 that when the pinch point occurs within the recuperating unit, the lowest temperature difference between the hot and cold sides occurs inside the recuperating unit. Based on the enthalpy changes of the hot and cold sides and heat balance, the following formula applies:

$Q_c={\stackrel{.}{m}}_c\left(h_{c,\mathrm{out}}-h_{c,\mathrm{in}}\right)={\stackrel{.}{m}}_c\Delta h_c={\stackrel{.}{m}}_c{c}_{p_{{,}_c}}\left(t_{c,\mathrm{out}}-t_{c,\mathrm{in}}\right)$ $\begin{array}{cc}{Q}_h={\stackrel{.}{m}}_h\left(h_{h,\mathrm{in}}-h_{h,\mathrm{out}}\right)={\stackrel{.}{m}}_h\Delta h_h={\stackrel{.}{m}}_h{c}_{p_{{,}_h}}\left(t_{h,\mathrm{out}}-t_{h,\mathrm{in}}\right)& \left(1\right)\end{array}$ $\begin{array}{cc}{Q}_c=Q_h,i.e.{\stackrel{.}{m}}_c{c}_{p_{{,}_c}}\left(t_{c,\mathrm{out}}-t_{c,\mathrm{in}}\right)={\stackrel{.}{m}}_h{c}_{p_{{,}_h}}\left(t_{h,\mathrm{out}}-t_{h,\mathrm{in}}\right)& \left(2\right)\end{array}$

Q_c and Q_h are heat changes of the cold and hot working fluids, respectively. {dot over (m)}_c and {dot over (m)}_h are the mass flow rates of the cold and hot side fluids per unit time, respectively. h_{c, out}, h_{c, in}, h_{n, out}, h_{n, in} represent the enthalpy values at the cold side outlet, cold side inlet, hot side outlet, and hot side inlet of the recuperating unit, respectively. Δh_c and Δh_h represent the changes in enthalpy for the cold and hot sides of the recuperating unit, respectively. C_p,c and C_p,h represent the specific heat at constant pressure for the cold and hot side working fluids, respectively. tc,out and tc,in are the outlet and inlet temperatures for the cold side fluid. th,out and th,in are the outlet and inlet temperatures for the hot side fluid. It can be seen from formula (2) that when the mass flow rates of the cold and hot side fluids in the recuperating unit are equal, the specific heat at constant pressure c_p,c and c_p,h of the cold and hot fluids play a decisive role in the temperature variation of the fluids. That is, the pinch point phenomenon inside the recuperating unit is closely related to the specific heat at constant pressure of the working fluid. FIG. 2 shows the variation of the specific heat at constant pressure along the cold and hot sides of the working fluids. It can be observed that the point where the specific heat curves of the cold and hot side fluids intersect corresponds to the location inside the recuperating unit where the pinch point occurs. In this case, the mass flow rates of the cold and hot side fluids and the specific heat at constant pressure are the same. Under the constraint of heat balance, the temperature change rate of the cold and hot side fluids is also the same. Therefore, the minimum temperature of the cold and hot side fluids occurs here, and the pinch point phenomenon appears. The specific heat at constant pressure is affected by factors such as fluid temperature and pressure, and in a supercritical CO₂ Brayton cycle system, the operational parameters like fluid temperature and pressure are related to the system parameters and process design.

On the other hand, it can be seen from formula (2) that the mass flow rate of the hot and cold side working fluids in the recuperating unit per unit time is also one of the direct factors influencing the temperature change of the cold and hot fluids. Once the specific heat at constant pressure reaches its optimal value, the occurrence of the pinch point phenomenon can be effectively avoided by adjusting the mass flow rate difference between the cold and hot sides, thereby achieving a significant temperature change along one side of the working fluid.

In summary, through the analysis of the heat balance formula, it can be determined that the occurrence of the pinch point in the heat exchange device is related to the mass flow rates and specific heat capacities at constant pressure of the cold and hot fluids during the heat exchange process. To avoid the pinch point, improvements to these two parameters during the operation of the heat exchanger can be implemented. Based on this analysis, the present application proposes a heat exchanger and a Brayton cycle power generation system to address the pinch point in a thermodynamic cycle.

Some embodiments of the present disclosure provide a heat exchanger based on solving the pinch point problem in thermodynamic cycles, the heat exchanger includes a heat exchange core 1 and a cover 2. The heat exchange core 1 comprises a plurality of cold side heat exchange plates 10 and a plurality of hot side heat exchange plates 20 stacked alternately. A first surface of the cold side heat exchange plate 10 defines multiple first flow channels 100 through first partitions, while the second surface of the hot side heat exchange plate 20, which faces the same direction as the first surface, defines several second flow channels 200 through second partitions. The cold side heat exchange plates 10 and/or the hot side heat exchange plates 20 each further comprises a branch flow channel 110. These branch channels 110 are set along the flow paths of all first flow channels 100 and/or all second flow channels 200, and communicate with all first flow channels 100 and/or all second flow channels 200 to merge or divert flow towards the cold side heat exchange plate 10 and/or the hot side heat exchange plate 20. The cover plate 2 is used for sealing the heat exchange core 1.

Specifically, referring to FIG. 3, FIG. 4, and FIG. 5, the heat exchanger includes a heat exchange core 1 and a cover plate 2 that covers the top and bottom of the heat exchange core 1. The first flow channel 100 and the second flow channel 200 on the top (upper) and bottom (lower) surfaces of the heat exchange core 1 can be sealed through the coverage of the cover plate 2. In the structure of the heat exchange core 1 formed by the alternately stacked cold side heat exchange plates 10 and hot side heat exchange plates 20, the cold side heat exchange plates 10 and the hot side heat exchange plates 20 are parallel to each other. The upper surface of the cold side heat exchange plate 10 (i.e., the surface close the top of the heat exchange core 1, and similar expressions in the following text refer to this surface) and the upper surface of the hot side heat exchange plate 20 each define the first flow channels 100 and the second flow channels 200 by partitions. The first flow channel 100 and the second flow channel 200 are each composed of several parallel sub-channels. The first flow channel 100 and the second flow channel 200 are separate and sealed from each other by the plate bodies of the cold side heat exchange plate 10 and the hot side heat exchange plate 20, which are alternately stacked. The orientation of the first flow channel 100 and the second flow channel 200 can be adapted to the actual heat exchange requirements.

FIG. 3, FIG. 4, and FIG. 5 illustrate one embodiment of the heat exchanger structure of the present application, using a recuperating unit as an example. In this embodiment, the alternately stacked cold side heat exchange plates 10 and hot side heat exchange plates 20 form a rectangular structure. The low-temperature working fluid enters from one end of the cold side heat exchange plate 10 along the length direction of the rectangular structure and exits from the other end, with the orientation of the first flow channel 100 being linear. The high-temperature working fluid enters from one end of the hot side heat exchange plate 20 along the width direction of the rectangular structure and exits from the other end, with the orientation of the second flow channel 200 being in a “Z” shape. The low-temperature and high-temperature working fluids independently flow in the first flow channel 100 and second flow channel 200 of different layers, respectively, and heat exchange occurs through the cold side heat exchange plate 10 and the hot side heat exchange plate 20, which serve as the heat conduction medium.

In the embodiment shown in FIG. 3, FIG. 4 and FIG. 5, the upper surface of the cold side heat exchange plate 10 is further provided with a branch flow channel 110. The branch flow channel 110 is arranged along the first flow channel 100 and is in communication with all the sub-channels. The branch flow channel 110 allows the introduction of working fluid at the same or different temperatures into the cold side heat exchange plate 10 to form a converging flow, thereby increasing the mass flow rate of the cold side working fluid in the heat exchanger or adjusting the working fluid temperature on the cold side. This configuration helps meet the parameters required for eliminating the pinch point. Specifically, the branch flow channel 110 can be connected to the sub-channels of the first flow channel 100 in a “fault” form, as shown in this embodiment, or set up in other forms such as the branch port 33, as long as it supports the influx of external working fluid or allows regulation for convergence.

It should be noted that the foregoing embodiments are merely examples of the heat exchanger of the present application using a recuperating unit as an example for ease of understanding. It should be understood by those skilled in the art that, by adjusting the orientation or configuration of the heat exchanger structure, it may also be applied as a cooler in a cycle system. The same structural principle can also serve to adjust the mass flow rate of the working fluid to thereby address the pinch point issue. For example, the branch flow channel 110 functions as a converging flow passage in the recuperating unit, while in the cooler it may function as a diverging flow passage. Accordingly, the branch flow channel 110 is not limited to being provided on the cold side heat exchange plate 10 as in the above embodiment; it may alternatively be provided on the hot side heat exchange plate 20, or on both the cold side heat exchange plate 10 and the hot side heat exchange plate 20. In other words, the heat exchanger of the present application is not limited to specific components or units within a cycle system in practical applications. So long as the occurrence of a pinch point due to heat exchange between low-temperature and high-temperature working fluids within a single device exists, the applicable structural relationship of the heat exchanger of the present application may be adaptively selected and adjusted to address the pinch point problem. Furthermore, when the heat exchanger of the present application is applied as a recuperating unit or a cooler, it is not limited to the rectangular structure exemplified in the foregoing embodiment, but may also take the form of a plate-type, shell-and-tube-type, finned-type, or other configurations that enable adjustment of the converging (or diverging) flow positions of the working fluid. Any application adopting a structure that is the same as or similar to that of the present application shall fall within the scope of protection claimed herein.

As a basic embodiment of the present application, the heat exchange core 1 of the heat exchanger is configured to include a plurality of cold side heat exchange plates 10 and a plurality of hot side heat exchange plates 20 alternately stacked. A plurality of first flow channels 100 are formed on a first surface of the cold side heat exchange plates 10 by first partitions, and a plurality of second flow channels 200 are formed on a second surface of the hot side heat exchange plates 20 by second partitions. The second surface is in the same direction as the first surface. This forms a main structure of the heat exchanger in which the first flow channels 100 and the second flow channels 200 are separate from each other, but heat exchange can be conducted via thermal conduction through the cold side heat exchange plates 10 and the hot side heat exchange plates 20. Furthermore, by providing the branch flow channel 110 on the cold side heat exchange plate 10 and/or the hot side heat exchange plate 20 (i.e., the branch flow channels 110 are provided on at least one of the two types of plates), the branch flow channel 110 is in communication with all of the first flow channels 100 and/or all of the second flow channels 200, forming an inlet for external working fluid or an outlet for internal working fluid on the heat exchange core 1. In this manner, the flow rate of the working fluid within the heat exchanger device can be regulated, and working fluids of different thermal states can be introduced through the branch flow channel 110 to achieve efficient heat exchange within the heat exchanger. This prevents problems such as deteriorated heat transfer between the cold side heat exchange plates 10 and the hot side heat exchange plates 20, or excessive local temperatures caused by insufficient temperature differences and the occurrence of pinch points inside the heat exchanger, which in turn can lead to excessive thermal stress. As a result, the heat exchange efficiency of the heat exchanger is directly and effectively improved in a self-adjustable manner.

In some embodiments, based on the foregoing embodiments, the heat exchanger further includes a heat exchange interface 3. The heat exchange interface 3 includes a cold side inlet 3-a, a cold side outlet 31-b, a hot side inlet 32-a, a hot side outlet 32-b, and a branch port 33, all of which are disposed on a side face of the heat exchange core 1. The cold side inlet 31-a and the cold side outlet 31-b are respectively connected to two ends of the first flow channels 100. The hot side inlet 32-a and the hot side outlet 32-b are respectively connected to two ends of the second flow channel 200. The cold side inlet 31-a and the hot side inlet 32-a are respectively located on opposite side surfaces of the heat exchange core 1, and the cold side outlet 31-b and the hot side outlet 32-b are respectively located on opposite side surfaces of the heat exchange core 1. The branch port 33 is connected to one end of the branch flow channel 110.

In the foregoing embodiment, the cold side heat exchange plates 10 and the hot side heat exchange plates 20 achieve heat exchange by virtue of the different inlet and outlet directions of the low-temperature working fluid and the high-temperature working fluid, which facilitates centralized input and output of the low-temperature or high-temperature working fluid on the heat exchanger. However, in practical applications, the heat exchanger is typically connected via pipelines for the transport and flow of the working fluid. Referring to FIG. 3 and FIG. 4, to enhance the adaptability of the heat exchanger of the present application, the heat exchange interface 3 including the cold side inlet 31-a, the cold side outlet 31-b, the hot side inlet 32-a, the hot side outlet 32-b, and the branch port 33 are respectively added at the inlet side and outlet side of the first flow channel 100, the inlet side and outlet side of the second flow channel 200, and the inlet side and outlet side of the branch flow channel 110, so as to facilitate the connection of the heat exchanger within devices and systems.

In an embodiment, the cold side inlet 31-a, the cold side outlet 31-b, the hot side inlet 32-a, the hot side outlet 32-b, and the branch port 33 are each formed by a header box structure, so as to enhance the sealing performance of the heat exchanger when connected within devices or systems, improve installation precision, and ensure that the heat exchange efficiency is not affected by connection defects.

In an embodiment, there are two branch ports 33, the branch flow channel 110 transversely communicates with all of the first flow channels 100 and/or all of the second flow channels 200, and each end of the branch flow channel 110 is connected to one of the branch ports 33.

The branch flow channel 110 shown in this embodiment is in communication with all of the sub-channels of the first flow channels 100 and/or all of the sub-channels of the second flow channels 200. Compared with an embodiment in which a single branch port 33 is used to achieve merging or splitting of flows, this configuration can increase the threshold for adjusting the working fluid flow rate using the heat exchanger of the present application, thereby enhancing heat exchange efficiency and addressing the pinch point issue.

In an embodiment, each branch port 33 is provided with a control valve configured to regulate the flow rate of the working fluid entering the branch flow channel 110. The provision of the control valves enhances the controllability of the heat exchanger in adjusting the mass flow rate of the working fluid, thereby offering improved adaptability and operational flexibility when implemented in specific devices or systems.

In an embodiment, a plurality of branch flow channels 110 are spaced apart by a preset distance on each of the cold side heat exchange plates 10 and/or each of the hot side heat exchange plates 20.

As shown in FIG. 4 and FIG. 5, the branch flow channels 110 may be arranged at intervals along the first flow channel 100 and/or the second flow channel 200. Correspondingly, in some embodiments, a plurality of branch ports 33 are also formed on the heat exchange core 1 at corresponding intervals. This configuration allows the application parameters of the heat exchanger to be adjusted based on actual conditions, such as the positions for flow merging or splitting and the mass flow rate of the working fluid inside the heat exchanger.

For the heat exchange process between the low-temperature working fluid in the cold side heat exchange plate 10 and the high-temperature working fluid in the hot side heat exchange plate 20, different flow path configurations of the first flow channel 100 and the second flow channel 200 are provided to enhance the heat exchange efficiency via a heat conduction medium (i.e., the plate body of the cold side heat exchange plate 10 or the hot side heat exchange plate 20). The heat exchange area between the low-temperature working fluid and the high-temperature working fluid can be increased by varying parameters such as the length and channel configuration of the first flow channel 100 and the second flow channel 200, thereby improving the heat exchange efficiency within the heat exchanger. The present application provides the following two embodiments to achieve this effect.

In a first embodiment, referring to FIGS. 5, 6, and 7, the partitions are a plurality of parallel strip-like baffles, and all of the first flow channels 100 and/or all of the second flow channels 200 form continuous flow paths in a straight, zigzag, or serpentine configuration through the partitions. In this embodiment, a plurality of parallel sub-channels are formed on the cold side heat exchange plate 10 or the hot side heat exchange plate 20 by the continuous strip-like baffles, thereby forming the first flow channel 100 or the second flow channel 200. The flow path of the working fluid in a zigzag or serpentine (S-shaped) sub-channel is significantly longer than that in a straight flow channel. During the heat exchange process, this facilitates a rapid temperature change of the working fluid within a limited travel distance and helps to prevent the occurrence of pinch point.

In a second embodiment, referring to FIG. 8, the partitions are a plurality of regularly distributed fins, and all of the first flow channels 100 and/or all of the second flow channels 200 form discontinuous but interconnected flow paths in the same direction through the partitions. In this embodiment, a plurality of sub-channels are formed on the cold side heat exchange plate 10 or the hot side heat exchange plate 20 by mutually independent fins, thereby constituting the first flow channel 100 or the second flow channel 200. Compared to the previous embodiment, the fin structures (e.g., teardrop-shaped fins in a top view) provide directionality to the flow channels, while the resulting discontinuous flow paths allow communication among the sub-channels, thereby increasing the mass flow capacity of the heat exchanger.

In an embodiment, the fin may be airfoil-shaped, diamond-shaped, or cylindrical.

In some embodiments, in order to achieve efficient heat exchange within the heat exchanger, various one-dimensional vortex generators, two-dimensional vortex generators, and three-dimensional vortex generators (not shown in the figures) may be provided in the first flow channel 100 and/or the second flow channel 200, as long as they do not impair the counterflow cutoff function. The one-dimensional vortex generators, the two-dimensional vortex generators and the three-dimensional vortex generators are conventional structures known in the prior art that possess counterflow cutoff functionality, and thus will not be described in detail described herein.

Some other embodiments of the present application further provide a Brayton cycle system. The Brayton cycle system includes a heat source, a thermoelectric conversion unit, a recuperating unit, a cooling unit, and a compression unit. The heat source, the thermoelectric conversion unit, the recuperating unit, the cooling unit, and the compression unit are in communication sequentially. The recuperating unit and the cooling unit include the heat exchanger in the foregoing embodiments.

FIG. 9 is a schematic diagram illustrating the logical connection of the Brayton cycle system according to the present application. The recuperating unit includes a recuperator, and the cooling unit includes a cooler. Both the recuperator and the cooler adopt the heat exchanger in the foregoing embodiments.

In some embodiments, the compression unit includes a main compressor and at least one re-compressor. An input end of the main compressor is connected to a hot side outlet 32-b of the cooling unit. An input end of the re-compressor is connected to a hot side outlet 32-b of the recuperating unit. An output end of the main compressor is connected to a cold side inlet 31-a of the recuperating unit. An output end of the re-compressor is connected to a branch port 33 of the recuperating unit.

Specifically, referring to FIG. 8, taking the case in which the recuperator employs the heat exchanger described in the foregoing embodiments as an example, the connection relationship among the recuperating unit, the cooling unit, and the compression unit is as follows. The hot side outlet 32-b of the recuperating unit branches into two paths by a diverter valve. One path is connected to the hot side inlet 32-a of the cooling unit. The hot side outlet 32-b of the cooling unit is connected to the input end of the main compressor. The output end of the main compressor is connected to the cold side inlet 31-a of the recuperating unit to form a loop. The other path is connected to the input end of the re-compressor, and the output end of the compressor is connected to the branch port 33 of the recuperating unit to form another cycle.

In applications, before entering the cooling unit, the high-temperature working fluid is divided into two streams by the diverter valve, thereby controllably reducing the mass flow rate of the high-temperature working fluid entering the cooling unit. Consequently, the mass flow rate of the working fluid compressed by the main compressor and entering from the cold side inlet 31-a of the recuperating unit is also reduced. On the other hand, the diverted portion of the high-temperature working fluid is compressed and cooled by the re-compressor, and then introduced into the recuperating unit through the branch port 33 of the recuperating unit. This allows adjustment of the mass flow rate of the working fluid on the cold side of the recuperating unit, thereby increasing the temperature difference between the cold side and the hot side of the recuperating unit, and thus avoiding the occurrence of a pinch point.

In an embodiment, the diverter valve includes a device controllably dividing the working fluid flow path into a plurality of branches, which may adopt devices such as a regulating valve, a stop valve, a stopcock valve and the like in the prior art to implement the branching function.

In an embodiment, if the heat exchanger used by the recuperating unit is provided with a plurality of branch ports 33 (that is, the foregoing embodiments with a plurality of branch flow channels 110), the connection between the output end of the compressor and the branch port 33 may also be split via the diverter valve and connected to each branch port 33. In cooperation with the control valves in the foregoing embodiments, this facilitates the introduction of working fluids with different temperatures and corresponding mass flow rates into the recuperating unit as needed. Further, when one of the plurality of branch ports 33 is selectively connected to form a confluence, the proportional distribution between the low-temperature recuperation section and the high-temperature recuperation section of the recuperator may be correspondingly adjusted, which is more conducive to eliminating pinch points (for detailed explanation of the principles, reference is made to the following description)

In some embodiments, on the basis of the above embodiments, temperature monitoring units are respectively provided at the hot side outlet 32-b of the cooling unit and the cold side outlet 31-b of the recuperating unit. The Brayton cycle system further comprises a measurement and control unit. The measurement and control unit is electrically connected to the control valve at each branch port 33 and the temperature monitoring units, and is configured to monitor the temperature at the hot side outlet 32-b of the cooling unit, the temperature at the cold side outlet 31-b of the recuperating unit, and to regulate the flow rate of the working fluid in the cooling unit and the recuperating unit.

In this embodiment, the measurement and control unit is added to the cycle system and electrically connected to the control valves at the branch ports 33 of the heat exchanger in the recuperating unit, to accurately control the mass flow of the working fluid entering the cold side of the recuperating unit in the cycle system, while also facilitating operation. In addition, the temperature monitoring units are provided at the cold side outlet 31-b of the recuperating unit and the hot side outlet 32-b of the cooling unit, and are electrically connected to the measurement and control unit as well. These temperature monitoring units provide visualized data conditions for the measurement and control unit to regulate the mass flow rate entering the recuperator based on the temperatures of the working fluid in different sections of the cycle system, thereby further enhancing the overall coordination of the cycle system.

In an embodiment, the temperature monitoring unit adopts a digital thermocouple, a resistance temperature detector and an infrared temperature sensor.

In some embodiments, referring to FIG. 10, the cooling unit in the Brayton cycle system also adopts the heat exchanger in the foregoing embodiments. Compared with the confluence function applied to the recuperating unit, the branch flow channel 110 of the heat exchanger serve a diverging function in this embodiment. Similarly, each tributary port 33 in the cooling unit is also electrically connected to the measurement and control unit to achieve the same effects as in the foregoing implementations, and thus will not be repeated here for the sake of brevity.

The following provides a further theoretical analysis of the heat exchanger and the Brayton cycle system in the foregoing embodiments in solving the pinch point problem, in combination with the related experimental data.

It is known from formula (2) that the occurrence of pinch points in the heat exchange device is related to two key factors: the mass flow rate of the working fluids and their specific heat at constant pressure during heat exchange. In thermodynamic theory, the specific heat at constant pressure is influenced by operational parameters such as the temperature and pressure of the working fluid. Upon further analysis, these operational parameters are, in turn, closely related to the system parameters and process design of the Brayton cycle.

FIGS. 11A-11D illustrate comparative data of the temperature and specific heat at constant pressure of the working fluids on both the hot and cold sides of a conventional recuperator under varying cold side pressures. Based on this data, it can be seen that when the hot side pressure of the recuperator is 7.9 MPa, pinch points occur across the entire range of cold side pressures from 9 MPa to 25 MPa. As the cold side pressure of the recuperator decreases, the average specific heat at constant pressure of the cold side working fluid increases, with a progressively larger variation range. When the cold side pressure is reduced to 9 MPa, only the hot side inlet section 32-a (approximately one-third of the total heat exchange length) effectively participates in heat exchange. In the remaining sections, the temperature profiles of the hot and cold working fluids become relatively flat, indicating a deterioration in heat transfer performance and poor heat transfer efficiency between the hot and cold fluids. This results in a significant waste of the heat exchange area within the recuperator. Therefore, to mitigate the pinch point issue in the recuperator, the cold side pressure of the recuperator working fluid should not be too low and should be set to at least greater than 12 MPa. From the perspective of overall thermal efficiency of the cycle system, a higher cold side pressure of the recuperator (which corresponds to the highest pressure in the cycle system, see FIG. 1) enables higher cycle efficiency. However, from the compressor design perspective (the cold side pressure of the recuperator corresponds to the outlet pressure of the compressor, see FIG. 1), a higher outlet pressure results in greater manufacturing complexity and cost. Accordingly, based on the above experimental data, a balanced consideration of the pinch point phenomenon in the recuperator, the cycle system thermal efficiency, and compressor manufacturing constraints suggests that the cold side pressure of the recuperator is preferably adjustable within a range of 12 MPa to 25 MPa. As for the hot side pressure of the recuperator (which corresponds to the turbine outlet pressure, see FIG. 1), selecting a pressure near the critical pressure of supercritical carbon dioxide (7.38 MPa) can yield the highest cycle efficiency from a thermodynamic perspective.

FIGS. 12A-12D illustrate comparative data of the temperature and specific heat at constant pressure of the working fluids on both the hot and cold sides of a typical conventional recuperator under different cold side working fluid inlet temperatures. It can be observed that as the cold side inlet temperature 31-a of the recuperator (corresponding to the compressor outlet temperature; see FIG. 1 of the cycle system) increases, the location of the pinch point within the recuperator gradually shifts toward the hot side outlet 32-b. When the cold side working fluid inlet temperature reaches 60° C., no pinch point occurs within the recuperator. At this point, the specific heat at constant pressure of the cold side working fluid remains consistently higher than that of the hot side working fluid. Therefore, from the perspective of eliminating pinch points in the recuperator, it is desirable to appropriately select the cold side working fluid inlet temperature to ensure that the specific heat at constant pressure of the cold side working fluid remains greater than that of the hot side working fluid. On the other hand, the cold side inlet temperature of the recuperator is limited by the compressor outlet temperature. Accordingly, when optimizing the Brayton cycle system based on experimental data, the influence of enthalpy rise within the compressor on the outlet working fluid temperature should be comprehensively considered, and efforts should be made to maximize the outlet temperature of the working fluid from the compressor. Moreover, it is evident from the comparison between FIGS. 11A-11D and FIGS. 12A-12D that increasing the cold side working fluid inlet temperature is more effective in eliminating the pinch point problem of the recuperator than increasing the cold side pressure. Therefore, priority should be given to raising the cold side inlet temperature 31-a as a more effective strategy to eliminate the pinch point within the recuperator.

In summary, in the Brayton cycle system proposed in the present application, the working fluid of the Brayton cycle system is supercritical carbon dioxide. The pressure at the cold side inlet 31-a of the recuperating unit ranges from 12 MPa to 25 MPa, the pressure at the hot side inlet of the recuperating unit is 7.38 MPa, and the temperature at the cold side inlet 31-a of the recuperating unit is greater than 50° C.

In the Brayton cycle system, if the pinch point remains unresolved after the temperature and pressure parameters have been set to their optimal values, then, as indicated by Equation (2), it is necessary to consider adjusting the mass flow rate of the working fluid within the heat exchange device. Specifically, reducing the mass flow rate of the cold side working fluid in the recuperator can offset the excessively high specific heat at constant pressure on the cold side, thereby inducing a more significant temperature variation of the cold side working fluid along the heat exchange path.

FIGS. 13A-13B illustrate comparative data of parameters of the hot side and cold side working fluids under different cold side flow rates in a typical conventional recuperator. It can be observed that when the mass flow rates of the hot side and cold side working fluids are equal, no pinch point occurs. However, the temperature variation of the working fluid near the hot side outlet 32-b is relatively flat. This indicates that pinch points are more likely to occur in the low-temperature recuperation section (as a counter-flow heat exchanger, the recuperator inherently comprises both a low-temperature and a high-temperature recuperation section), where heat exchange efficiency is low and the heat transfer area of the recuperator is not fully utilized. In contrast, after flow splitting is applied to the working fluid on the cold side, the thermal capacity (m_cc_p,c) of the cold side working fluid decreases, resulting in a significant temperature change in, the working fluid on the cold side. The cold side working fluid thereby achieves a higher outlet temperature, and the overall temperature distribution in the recuperator becomes more rational. Consequently, the heat exchange efficiency along the recuperator improves, and the overall heat transfer area is utilized more effectively.

The heat exchanger in the present application is used as a recuperator in the cycle system and adopts a diverging-and-converging flow configuration (i.e., the configuration in which the re-compressor is connected via flow splitting to the branch ports 33 as described in in the foregoing embodiment), so that a high mass flow rate on the hot side and a low mass flow rate on the cold side can be achieved in the low-temperature recuperation section. This operating mode effectively avoids the occurrence of pinch points in the low-temperature section of the recuperator. FIG. 14 shows data on the parameter variations in the high-temperature and low-temperature recuperation sections of the recuperator (recuperating unit) within the Brayton cycle system provided by the present application. It can be seen that, after adopting the flow-splitting design, the pinch point phenomenon within the recuperator is eliminated. The overall temperature distribution of the working fluid in the recuperator becomes more rational, the heat exchange area of the recuperator is fully utilized, and a higher heat exchange efficiency is achieved.

It is specifically noted that the above-mentioned use of the heat exchanger as a recuperator (recuperating unit) is intended solely for illustrative convenience in the context of experimental observations. Based on the relevant principles, those skilled in the art may reasonably deduce that similar results would be achieved when the heat exchanger of the present application is used as a cooler (cooling unit). Therefore, related data are not provided herein.

The above detailed description of specific embodiments of the present application is intended to serve as illustrative examples only, and the present application is not limited to the specific embodiments described above. Various equivalent modifications and substitutions made by those skilled in the art without departing from the spirit and scope of the present application shall also fall within the scope of protection of the present application. Accordingly, all equivalent transformations, modifications, and improvements made within the spirit and principles of the present application are intended to be covered by the scope of the present application.

Claims

1. A heat exchanger based on a solution to a pinch point in a thermodynamic cycle, comprising:

a heat exchange core, wherein the heat exchange core comprises a plurality of cold side heat exchange plates and a plurality of hot side heat exchange plates stacked alternately; a first surface of each cold side heat exchange plate defines a plurality of first flow channels by first partitions; a second surface, which faces the same direction as the first surface, of each hot side heat exchange plate defines a plurality of second flow channels by second partitions; the cold side heat exchange plates and/or the hot side heat exchange plates further comprise branch flow channels; the branch flow channels are disposed along flow paths of all the first flow channels and/or all the second flow channels, and are in fluid communication with all the first flow channels and/or all the second flow channels, to converge or split flows within the cold side heat exchange plates and/or the hot side heat exchange plates; and

a cover plate, configured to seal the heat exchange core.

2. The heat exchanger according to claim 1, wherein the heat exchanger further comprises a heat exchange interface, the heat exchange interface comprises a cold side inlet, a cold side outlet, a hot side inlet, a hot side outlet and a branch port which are arranged on a side face of the heat exchange core, the cold side inlet and the cold side outlet are respectively connected to two ends of the second heat channels, the hot side inlet and hot side outlet are respectively connected to two ends of the second flow channels, the cold side inlet and the hot side inlet are respectively located on two opposite sides of the heat exchange core, the cold side outlet and the hot side outlet are respectively located on two opposite sides of the heat exchange core, and the branch port is connected to one end of the branch flow channels.

3. The heat exchanger according to claim 2, wherein the branch ports are provided in pairs, and the branch flow channels transversely penetrate through all the first flow channels and/or all the second flow channels, with two ends of the branch flow channels are connected to respective branch ports.

4. The heat exchanger according to claim 3, wherein each branch port is provided with a control valve to regulate flow entering the branch flow channel.

5. The heat exchanger according to claim 1, wherein a plurality of the branch flow channels are arranged at preset intervals on each cold side heat exchange plate and/or each hot side heat exchange plate.

6. The heat exchanger according to claim 1, wherein the partitions are a plurality of elongated grid plates arranged in parallel, and all the first flow channels and/or all the second flow channels are formed as continuous linear, zigzag, or meandering flow channels through the partitions.

7. The heat exchanger according to claim 1, wherein the partitions are a plurality of regularly distributed fins, and all the first flow channels and/or all the second flow channels are formed as aligned and interconnected non-continuous flow channels through the partitions.

8. A Brayton cycle system, comprising:

a heat source;

a thermoelectric conversion unit;

a recuperating unit;

a cooling unit; and

a compression unit, wherein the heat source, the thermoelectric conversion unit, the recuperating unit, the cooling unit, and the compression unit are in communication sequentially, the recuperating unit and the cooling unit comprise the heat exchanger according to claim 1.

9. The Brayton cycle system according to claim 8, wherein the compression unit comprises a main compressor and at least one re-compressor, an input end of the main compressor is connected to a hot side outlet of the cooling unit, an input end of the re-compressor is connected to a hot side outlet of the recuperating unit, an output end of the main compressor is connected to a cold side inlet of the recuperating unit, and an output end of the re-compressor is connected to a branch port of the recuperating unit.

10. The Brayton cycle system according to claim 9, wherein the hot side outlet of the cooling unit and a cold side outlet of the recuperating unit each are provided with a temperature monitoring unit, the Brayton cycle system further comprises a measurement and control unit, the measurement and control unit is electrically connected to the control valve on each branch port and the temperature monitoring unit, and is configured to monitor the temperature at the hot side outlet of the cooling unit and the temperature at the cold side outlet of recuperating unit, and regulate a flow rate of a working fluid inside the cooling unit and the recuperating unit.

11. The Brayton cycle system according to claim 10, wherein a working fluid of the Brayton cycle system is supercritical carbon dioxide, a pressure at the cold side inlet of the recuperating unit is 12 MPa to 25 MPa, the pressure at the hot side inlet of the recuperating unit is 7.38 MPa, and a temperature at the cold side inlet of the recuperating unit is greater than 50° C.