Heat exchanger based on solution of pinch point problem in thermodynamic cycle, and brayton cycle system

Abstract

Disclosed in the present application are a heat exchanger based on solution of a pinch point problem in a thermodynamic cycle, and a Brayton cycle system. The heat exchanger comprises a heat exchange core body and cover plates, wherein the heat exchange core body is provided with several cold-side heat exchange plates and several hot-side heat exchange plates which are alternately layered, and first heat exchange flow channels and second heat exchange flow channels are respectively formed on the cold-side heat exchange plates and the hot-side heat exchange plates by means of separators; branch flow channels are further provided along all the first heat exchange flow channels and / or all the second heat exchange flow channels on the cold-side heat exchange plates and / or the hot-side heat exchange plates, and communicate all the first heat exchange flow channels and / or all the second heat exchange flow channels for flow convergence or divergence on the cold-side heat exchange plates and / or the hot-side heat exchange plates; and the heat exchange core body is sealed by means of the cover plates. By means of the structural cooperation of the first heat exchange flow channels, the second heat exchange flow channels and the branch flow channels that are located on the alternately-arranged cold-side heat exchange plates and hot-side heat exchange plates, the present application improves the heat exchange efficiency of the heat exchanger, avoiding the impact of a pinch point problem.

Description

Heat exchanger and Brayton cycle system based on solution of thermodynamic cycle pinch point problem

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 27, 2023, with application number 202311814242X and application name “Heat exchanger and Brayton cycle system based on solution to thermodynamic cycle pinch point problem”, all contents of which are incorporated by reference into the application. Technical Field

[0002] The present application relates to the field of thermodynamic cycle technology, and in particular to a heat exchanger and a Brayton cycle system based on solving the pinch point problem of thermodynamic cycle. Background Art

[0003] In a thermal cycle system, the regenerator and cooler are the core heat transfer devices in the circulation system. The regenerator recovers some of the high-value heat from the exhaust gas at the turbine outlet to preheat the working fluid. The heat recovery process can increase the temperature of the working fluid entering the heat source, reduce the irreversible heat loss of the working fluid in the heat source, and improve the thermal efficiency of the cycle. The main function of the cooler is to serve as a circulating cold source to achieve system heat-to-work conversion and provide low-temperature working fluid for the compressor. Existing thermal cycle systems may have a pinch point phenomenon within the regenerator, cooler, and other heat exchangers. The pinch point refers to the location where the minimum temperature difference between the cold and hot fluids in the heat exchanger occurs. Due to changes in the physical properties of the working fluid, the minimum temperature difference between the cold and hot fluids may occur in the middle of the heat exchanger, rather than at the cold or hot end outlets. If the pinch point occurs in the middle of the heat exchanger, it may lead to unfavorable conditions such as increased heat exchanger size and decreased heat transfer efficiency. This heat transfer deterioration problem caused by the minimum temperature difference between the cold and hot fluids appearing in the middle of the heat exchanger is called the pinch point problem. When the pinch point problem occurs in heat exchanger equipment, including regenerators and coolers, it will cause the heat transfer on the hot and cold sides of the heat exchanger equipment to deteriorate, the heat transfer efficiency to decrease, and the temperature at a local location to be too high, resulting in excessive thermal stress in the heat exchanger and detrimental to the circulation process of the thermal system.

[0004] Application Contents

[0005] The main purpose of this application is to provide a heat exchanger and a Brayton cycle system based on solving the pinch point problem of the thermodynamic cycle, so as to solve the pinch point problem that often occurs in heat exchange equipment in the prior art.

[0006] To achieve the above objectives, the present application provides the following technical solution: a heat exchanger based on solving the thermodynamic cycle pinch point problem, the heat exchanger comprising:

[0007] A heat exchange core, the heat exchange core comprising a plurality of cold-side heat exchange plates and a plurality of hot-side heat exchange plates arranged in staggered layers, wherein a first surface of the cold-side heat exchange plate is formed with a first partition to form a plurality of first heat exchange channels, and a second surface of the hot-side heat exchange plate, which is in the same direction as the first surface, is formed with a second partition to form a plurality of second heat exchange channels; the cold-side heat exchange plate and / or the hot-side heat exchange plate further comprising a branch flow channel, the branch flow channel being arranged along all the first heat exchange channels and / or all the second heat exchange channels and connecting all the first heat exchange channels and / or all the second heat exchange channels to converge or diverge to the cold-side heat exchange plate and / or the hot-side heat exchange plate;

[0008] A cover plate is used to seal the heat exchange core.

[0009] Optionally, the heat exchanger also includes a heat exchange interface, which includes a cold side inlet, a cold side outlet, a hot side inlet, a hot side outlet and a branch port arranged on the side of the heat exchange core, the cold side inlet and the cold side outlet are respectively connected to the two ends of the first heat exchange channel, the hot side inlet and the hot side outlet are respectively connected to the two ends of the second heat exchange channel, the cold side inlet and the hot side inlet are respectively located on the two sides of the heat exchange core, the cold side outlet and the hot side outlet are respectively located on the two sides of the heat exchange core, and the branch port is connected to one end of the branch channel.

[0010] Optionally, two branch ports are provided, the branch flow channel transversely passes through all the first heat exchange channels and / or all the second heat exchange channels, and each end of the branch flow channel is connected to a branch port.

[0011] Optionally, each branch outlet is provided with a control valve to control the flow rate entering the branch flow channel.

[0012] Optionally, a plurality of branch flow channels are provided on each cold-side heat exchange plate and / or each hot-side heat exchange plate at preset intervals.

[0013] Optionally, the partition is a plurality of parallel long grid plates, and all the first heat exchange channels and / or all the second heat exchange channels pass through the partition to form a straight line, a broken line or a circuitous continuous channel.

[0014] Optionally, the partition is a plurality of regularly distributed fins, and all the first heat exchange channels and / or all the second heat exchange channels form unidirectional and interconnected discontinuous channels through the partition.

[0015] On the other hand, the present application also provides a Brayton cycle system, which includes a heat source, a thermoelectric conversion unit, a heat recovery unit, a cooling unit, and a compression unit. The heat source, the thermoelectric conversion unit, the heat recovery unit, the cooling unit, and the compression unit are connected in a cycle in sequence, and the heat recovery unit and the cooling unit include a heat exchanger as described in any of the previous items.

[0016] Optionally, the compression unit includes a main compressor and at least one re-compressor, the input end of the main compressor is connected to the hot side outlet of the cooling unit, and the input end of the re-compressor is connected to the hot side outlet of the heat recovery unit; the output end of the main compressor is connected to the cold side inlet of the heat recovery unit, and the output end of the re-compressor is connected to the branch port of the heat recovery unit.

[0017] Optionally, a temperature monitoring unit is provided on the hot side outlet of the cooling unit and the cold side outlet of the heat regeneration unit, respectively. The Brayton cycle system also includes a measurement and control unit, which is electrically connected to the control valve on each branch outlet and the temperature monitoring unit, respectively, and is used to monitor the hot side outlet temperature of the cooling unit, the cold side outlet temperature of the heat regeneration unit, and adjust and control the internal working fluid flow of the cooling unit and the heat regeneration unit.

[0018] Optionally, the working fluid of the Brayton cycle system is supercritical carbon dioxide, the cold side inlet pressure of the heat recovery unit is 12MPa~25MPa, the cold side inlet pressure of the heat recovery unit is 7.38MPa, and the cold side inlet temperature of the heat recovery unit is greater than 50°C.

[0019] The heat exchanger of the present application includes a heat exchange core and a cover plate, wherein the cover plate is used to seal the heat exchange core; the heat exchange core is arranged as a plurality of cold-side heat exchange plates and a plurality of hot-side heat exchange plates arranged in staggered layers, and a plurality of first heat exchange flow channels are formed on the first surface of the cold-side heat exchange plate by a first partition, and a plurality of second heat exchange flow channels are formed on the second surface of the hot-side heat exchange plate which is in the same direction as the first surface, so that the first heat exchange flow channels and the second heat exchange flow channels are isolated from each other but can be used as heat transfer media for heat exchange by using the cold-side heat exchange plate and the hot-side heat exchange plate as the heat transfer medium; further, the present application also provides a heat exchanger main structure by arranging branch flow channels (i.e., cold-side heat exchange plate or hot-side heat exchange plate) on the cold-side heat exchange plate and / or the hot-side heat exchange plate At least one of the two plates is provided with a branch flow channel), so that the branch flow channel connects all the first heat exchange flow channels and / or all the second heat exchange flow channels, forming an inlet for external working fluid or an outlet for internal working fluid on the heat exchange core, thereby adjusting the flow rate of the working fluid in the heat exchanger equipment, and at the same time, working fluids with different heat contents can be mixed into the branch flow channel for efficient heat exchange inside the heat exchanger, thereby avoiding problems such as deterioration of heat transfer on the cold and hot sides of the heat exchanger due to too small a temperature difference between the cold side heat exchange plate and the hot side heat exchange plate, the pinch point being located inside the heat exchanger, and excessive thermal stress in the heat exchanger caused by excessively high temperature at a local location, thereby directly and effectively improving the heat exchange efficiency of the heat exchanger in a self-regulatory manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG1 is a schematic diagram of the principle of an existing simplified Brayton cycle system;

[0021] Figure 2 shows the changes in parameters along the hot and cold sides of the regenerator when a pinch point occurs under typical parameter conditions;

[0022] FIG3 is a schematic diagram of the overall structure of an embodiment of a heat exchanger of the present application;

[0023] FIG4 is a schematic diagram of a partially disassembled heat exchange core of an embodiment of the heat exchanger of the present application;

[0024] Figure 5 is an enlarged schematic diagram of point A in Figure 4;

[0025] FIG6 is a schematic structural diagram of an embodiment of the first heat exchange channel and / or the second heat exchange channel of the heat exchanger of the present application;

[0026] FIG7 is a schematic structural diagram of an embodiment of the first heat exchange channel and / or the second heat exchange channel of the heat exchanger of the present application;

[0027] FIG8 is a schematic structural diagram of an embodiment of the first heat exchange channel and / or the second heat exchange channel of the heat exchanger of the present application;

[0028] FIG9 is a logical connection diagram of an embodiment of a Brayton cycle system provided by the present application;

[0029] FIG10 is a schematic diagram of the logical connections of an embodiment of a Brayton cycle system provided by the present application;

[0030] Figure 11 shows the comparative data of the changes in the working fluid temperature and specific heat at constant pressure on the cold and hot sides of a typical existing regenerator when the cold side pressure is different;

[0031] Figure 12 shows the comparative data of the changes in the working fluid temperature and specific heat at constant pressure along the cold and hot sides of a typical existing regenerator when the working fluid inlet temperature on the cold side is different;

[0032] Figure 13 shows the comparison of parameters of working fluids along the hot and cold sides of a typical existing regenerator when the cold side flow rate is different;

[0033] FIG14 is a diagram showing parameter variation data along the high-temperature regenerative section and the low-temperature regenerative section of the regenerator (regenerative unit) in the Brayton cycle system provided by this application;

[0034] Explanation of the serial numbers: 1. Heat exchange core; 10. Cold side heat exchange plate; 100. First heat exchange channel; 110. Branch channel; 20. Hot side heat exchange plate; 200. Second heat exchange channel; 2. Cover plate; 3. Heat exchange interface; 31-a. Cold side inlet; 31-b. Cold side outlet; 32-a. Hot side inlet; 32-b. Hot side outlet; 33. Branch port.

[0035] The realization of the objectives, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0037] The terms "first," "second," and "third" in this application are used only for descriptive purposes and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of such features. In the description of this application, "multiple" means at least two, for example, two, three, etc., unless otherwise specifically defined. All directional indications in the embodiments of this application (such as up, down, left, right, front, back...) are only used to explain the relative positional relationship, movement, etc. between the components under a specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indications also change accordingly. In addition, the terms "including" and "having," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units that are not listed, or may optionally include other steps or units that are inherent to these processes, methods, products, or devices.

[0038] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0039] Thermal power generation usually uses water vapor as a heat transfer medium, that is, water is heated and pressurized, a turbine is used to convert thermal energy into mechanical energy, and then a generator is used to convert mechanical energy into electrical energy. In the current field of thermal power generation, supercritical carbon dioxide (sCO2) is widely used as a working fluid for thermal power generation due to its low critical temperature and pressure, liquid density and gas fluidity, and high heat transfer efficiency. Compared with previous gas and steam working fluids, it has more application and research value due to the above advantages. At present, it is more common to use supercritical carbon dioxide as a working fluid in a Brayton cycle system for thermal cycle power generation. Figure 1 shows a simplified schematic diagram of the Brayton cycle system. The Brayton cycle system generally includes a heat source, a turbine, a regenerator, a cooler and a compressor that are connected in a cycle. Among them, the output of the turbine is generally connected to a generator to convert mechanical energy into electrical energy, while the compressor is generally connected to an electric motor, which compresses the working fluid under the drive of the electric motor; the regenerator is used to recover part of the high-value heat of the exhaust gas at the turbine outlet to preheat the working fluid. The heat recovery process can increase the temperature of the working fluid entering the heat source, reduce the irreversible heat absorption loss of the working fluid in the heat source, and improve the thermal efficiency of the cycle; and the main function of the cooler is to serve as a circulating cold source to realize the system heat-to-work conversion, provide low-temperature working fluid for the compressor, and utilize the physical property changes of supercritical carbon dioxide near the critical point to reduce compression power consumption and improve cycle efficiency.

[0040] For example, in a Brayton cycle system, the presence of heat exchangers such as regenerators and coolers inevitably creates pinch points. This occurs when the minimum temperature difference in a heat exchanger occurs not at its ends but somewhere within the heat exchanger. This can lead to adverse effects such as reduced heat transfer efficiency and increased design complexity. Therefore, avoiding pinch points in heat exchangers such as regenerators and coolers is crucial for improving efficiency and ensuring safety in various thermal power generation systems, including but not limited to the aforementioned Brayton cycle system using supercritical carbon dioxide as a working fluid.

[0041] It should be noted that, for ease of understanding, the following description of the heat exchanger in this application will be explained 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 this application. Those skilled in the art should understand that devices in other thermal power generation systems that employ the same or similar structures to the heat exchanger in this application to address pinch point issues are also included within the scope of protection of this application.

[0042] The pinch point phenomenon in heat exchange equipment occurs because the heat capacity flow rate (the product of mass flow rate and constant pressure specific heat, mCp) of the two fluids involved in the heat exchange in the heat exchanger changes dramatically (for example, a phase change during the heat exchange process will cause the constant pressure specific heat to be infinite), or because the temperature curve is no longer approximately a straight line due to changes in physical properties, the minimum temperature difference in the heat exchange process occurs inside the heat exchanger. Figure 2 shows the parameter changes along the hot and cold sides of the regenerator under typical parameter conditions. It can be observed from Figure 2 that when the pinch point phenomenon occurs in the regenerator, the lowest temperature difference between the hot and cold sides of the working fluid occurs inside the regenerator. According to the change in the enthalpy value of the hot and cold sides and the heat balance, the following formula is obtained:

[0043] Q c =Q h ,Right now

[0044] Among them, Q c , Q h are the heat changes of the cold and hot working fluids, and are the mass flow rates of the hot and cold working fluids per unit time, h c，out 、h c，in 、h h，out 、h h，in are the enthalpy values ​​of the cold side outlet, cold side inlet, hot side outlet, and hot side inlet of the regenerator, Δh c , Δh h are the enthalpy changes of the cold side and hot side of the regenerator, c p,c and c p,h are the constant pressure specific heat of the working fluid on the cold and hot sides respectively, and t c,out and t c,in are the inlet and outlet temperatures of the cold side working medium, t h,out and t h,in are the inlet and outlet temperatures of the hot side working medium respectively. From formula (2), we can see that when the mass flow of the working medium on the hot and cold sides of the regenerator is the same, the constant pressure specific heat of the hot and cold working medium c p,c and c p,h The pinch point phenomenon within the regenerator is crucial for the temperature variations of the hot and cold working fluids. This phenomenon is closely related to the constant-pressure specific heat of the working fluid. Figure 2 shows the variations in the constant-pressure specific heat of the working fluids on the hot and cold sides. The intersection of the constant-pressure specific heat curves for the hot and cold sides corresponds to the location of the pinch point within the regenerator. At this point, the mass flow rate and constant-pressure specific heat of the working fluids on the hot and cold sides are identical. Under the constraints of thermal equilibrium, the rates of temperature change on both sides are also equal, resulting in the lowest temperatures on both sides, and the pinch point phenomenon. Constant-pressure specific heat is affected by operating parameters such as working fluid temperature and pressure. These operating parameters, in the supercritical carbon dioxide Brayton cycle system, are in turn related to parameter and process design.

[0045] On the other hand, it can be seen from formula (2) that the mass flow rate of the working fluid on the hot and cold sides of the regenerator per unit time is also one of the direct influencing factors of the temperature change of the hot and cold working fluids. After the constant pressure specific heat reaches the optimal value, the mass flow rate difference between the hot and cold sides can be adjusted to achieve a large change in the temperature of the working fluid on one side along the process, thereby effectively avoiding the occurrence of the pinch point phenomenon.

[0046] In summary, through analysis of the heat balance formula, it can be determined that the pinch point phenomenon in heat exchange equipment is related to the mass flow rate and constant-pressure specific heat on the cold and hot sides of the heat exchanger when different heat media are exchanging heat. The pinch point phenomenon can be avoided by improving these two parameters during the heat exchanger's application. Based on this analysis, this application proposes a heat exchanger and Brayton cycle power generation system that can be used to resolve the pinch point problem in thermal cycles.

[0047] Some embodiments of the present application provide a heat exchanger based on solving the thermodynamic cycle pinch point problem, the heat exchanger comprising: a heat exchange core 1 and a cover plate 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 arranged in staggered layers, the first surface of the cold-side heat exchange plate 10 is formed with a first partition to form a plurality of first heat exchange channels 100, and the second surface of the hot-side heat exchange plate 20, which is in the same direction as the first surface, is formed with a second partition to form a plurality of second heat exchange channels 200; the cold side heat exchange plate 10 and / or the hot side heat exchange plate 20 also include a branch flow channel 110, and the branch flow channel 110 is arranged along all the first heat exchange channels 100 and / or all the second heat exchange channels 200 and connects all the first heat exchange channels 100 and / or all the second heat exchange channels 200 to converge or diverge to the cold side heat exchange plate 10 and / or the hot side heat exchange plate 20; the cover plate 2 is used to seal the heat exchange core 1.

[0048] Specifically, referring to Figures 3, 4 and 5, the heat exchanger includes a heat exchange core 1 and a cover plate 2 covering the upper and lower surfaces of the heat exchange core 1. The first heat exchange flow channel 100 and the second heat exchange flow channel 200 in the top (upper) surface and the bottom (lower) surface of the heat exchange core 1 can be sealed by covering and sealing the cover plate 2; in the heat exchange core 1 structure formed by a plurality of cold side heat exchange plates 10 and a plurality of hot side heat exchange plates 20 being staggered, the cold side heat exchange plates 10 and the hot side heat exchange plates 20 are parallel to each other, and the upper surface of the cold side heat exchange plate 10 (the side close to the top surface of the heat exchange core 1, and the rear side) is parallel to each other. The first heat exchange channel 100 and the second heat exchange channel 200 are respectively formed on the upper surface of the cold side heat exchange plate 10 and the hot side heat exchange plate 20 by partitions, and the first heat exchange channel 100 and the second heat exchange channel 200 are composed of a plurality of parallel sub-channels; wherein, the first heat exchange channel 100 and the second heat exchange channel 200 are isolated and sealed by the plate bodies of the staggered cold side heat exchange plates 10 and the hot side heat exchange plates 20; the direction of the first heat exchange channel 100 and the second heat exchange channel 200 can be adjusted accordingly according to actual heat exchange needs.

[0049] Figures 3, 4 and 5 take a regenerator as an example to illustrate an embodiment of the heat exchanger structure of the present application. In this embodiment, the staggered cold side heat exchange plates 10 and the hot side heat exchange plates 20 form a rectangular structure. The low-temperature working medium enters the cold side heat exchange plate 10 along one end of the long direction of the rectangular parallelepiped and flows out at the other end, and the direction of the first heat exchange channel 100 is straight. The high-temperature working medium enters the hot side heat exchange plate 20 from one end of the wide direction of the rectangular parallelepiped and flows out at the other end, and the direction of the second heat exchange channel 200 is "Z"-shaped. The low-temperature working medium and the high-temperature working medium flow independently in the first heat exchange channel 100 and the second heat exchange channel 200 of different layers respectively and can exchange heat with the heat conduction medium of the cold side heat exchange plate 10 and the hot side heat exchange plate 20.

[0050] In the embodiments shown in Figures 3, 4, and 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 heat exchange channel 100 and connects all sub-channels. Through the branch flow channel 110, working fluids of the same or different temperatures can be introduced into the cold-side heat exchange plate 10 to form a convergence, thereby increasing the mass flow rate of the working fluid on the cold side of the heat exchanger, or adjusting the working fluid temperature on the cold side of the heat exchanger, thereby meeting the corresponding parameter requirements for pinch point elimination. Specifically, the branch flow channel 110 can be connected to the sub-channels of the first heat exchange channel 100 in the form of a "fault" in this embodiment, or it can be provided in other entry forms such as a branch port 33, as long as it supports the influx of working fluids or adjustments outside the heat exchange core 1.

[0051] It should be noted that the aforementioned embodiments are merely specific demonstrations of the heat exchanger structure of the present application using a regenerator as an example for ease of understanding. Those skilled in the art should understand that by adjusting the direction or changing the configuration of the heat exchanger structure, it can also be applied as a cooler in a circulation system. Its structure, based on the same principle, can also adjust the mass flow rate of the working fluid and thereby resolve the pinch point problem. For example, the branch flow channel 110 serves as a confluence in the regenerator and as a diversion channel in the cooler. Accordingly, the branch flow channel 110 is not limited to being disposed on the cold-side heat exchange plate 10 in the aforementioned embodiment. It can also be disposed 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 in a circulation system during actual application. As long as a pinch point phenomenon occurs due to heat exchange between a low-temperature working fluid and a high-temperature working fluid in the same device, the applicable structural relationship of the heat exchanger of the present application can be adaptively selected to resolve the pinch point problem. Furthermore, when the heat exchanger of this application is used as a regenerator or cooler, it is not limited to the rectangular parallelepiped shape shown in the examples in the aforementioned embodiments. It can also be a plate-type, shell-and-tube-type, fin-type, or other types of configurations that can achieve the function of adjusting the position of the working fluid confluence (or diversion). As long as the structural principles identical or similar to those of this application are applied, they shall be included in the scope of protection claimed by this application.

[0052] As a basic embodiment of the present application, the heat exchange core 1 of the heat exchanger is set to a plurality of cold side heat exchange plates 10 and a plurality of hot side heat exchange plates 20 arranged in staggered layers, and a plurality of first heat exchange channels 100 are formed on the first surface of the cold side heat exchange plate 10 by a first partition, and a plurality of second heat exchange channels 200 are formed on the second surface of the hot side heat exchange plate 20 in the same direction as the first surface by a second partition, so as to form a heat exchanger main structure in which the first heat exchange channels 100 and the second heat exchange channels 200 are isolated from each other but heat exchange can be performed using the cold side heat exchange plate 10 and the hot side heat exchange plate 20 as heat conduction medium; further, by setting a branch channel 110 on the cold side heat exchange plate 10 and / or the hot side heat exchange plate 20 (that is, the cold side heat exchange plate 10 or the hot side heat exchange plate 20 At least one of the two plates is provided with a branch flow channel 110), so that the branch flow channel 110 is connected to all the first heat exchange channels 100 and / or all the second heat exchange channels 200, forming an inlet for external working fluid or an outlet for internal working fluid on the heat exchange core 1, thereby adjusting the flow rate of the working fluid in the heat exchanger equipment, and at the same time, working fluids with different heat contents can be mixed into the branch flow channel 110 for efficient heat exchange inside the heat exchanger, thereby avoiding problems such as deterioration of heat transfer on the cold and hot sides of the heat exchanger due to the small temperature difference between the cold side heat exchange plate 10 and the hot side heat exchange plate 20, the pinch point being located inside the heat exchanger, and excessive thermal stress in the heat exchanger caused by excessively high temperature at a local location, thereby directly and effectively improving the heat exchange efficiency of the heat exchanger in an autonomously controllable manner.

[0053] In some embodiments, based on the above embodiments, the heat exchanger further includes a heat exchange interface 3, which includes a cold side inlet 31-a, a cold side outlet 31-b, a hot side inlet 32-a, a hot side outlet 32-b and a branch port 33 arranged on the side of the heat exchange core 1, the cold side inlet 31-a and the cold side outlet 31-b are respectively connected to the two ends of the first heat exchange channel 100, and the hot side inlet 32-a and the hot side outlet 32-b are respectively connected to the two ends of the second heat exchange channel 200, the cold side inlet 31-a and the hot side inlet 32-a are respectively located on the two sides of the heat exchange core 1, the cold side outlet 31-b and the hot side outlet 32-b are respectively located on the two sides of the heat exchange core 1, and the branch port 33 is connected to one end of the branch channel 110.

[0054] The cold side heat exchange plate 10 and the hot side heat exchange plate 20 shown in the aforementioned embodiment realize heat exchange through the different inlet and outlet directions of the low-temperature working fluid and the high-temperature working fluid, which is convenient for the centralized input and output of the low-temperature working fluid or the high-temperature working fluid on the heat exchanger. However, when the heat exchanger is used in actual equipment, the transmission flow of the working fluid is usually realized through pipeline connection. See Figures 3 and 4. In order to improve the adaptability of the heat exchanger of the present application, a heat exchange interface 3 including a cold side inlet 31-a, a cold side outlet 31-b, a hot side inlet 32-a, a hot side outlet 32-b and a branch port 33 is added to the inlet and outlet sides of the first heat exchange channel 100 and the inlet and outlet sides of the second heat exchange channel 200 and the inlet and outlet sides of the branch channel 110 to facilitate the connection of the heat exchanger in the equipment and system.

[0055] Optionally, 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 all formed by a pipe box structure to enhance the sealing of the heat exchanger in the equipment and system, improve the installation accuracy, and ensure that the heat exchange efficiency is not affected by connection defects.

[0056] Optionally, two branch ports 33 are provided, the branch channel 110 transversely passes through all the first heat exchange channels 100 and / or all the second heat exchange channels 200 , and each end of the branch channel 110 is connected to a branch port 33 .

[0057] The branch flow channel 110 shown in this embodiment connects all the sub-channels of the first heat exchange channel 100 and / or all the sub-channels of the second heat exchange channel 200. Compared with the embodiment in which a single branch port 33 is used to achieve convergence or diversion, the threshold for adjusting the working fluid flow rate using the heat exchanger of the present application can be increased, thereby improving the heat exchange efficiency and solving the pinch point problem.

[0058] Optionally, a control valve is provided on each branch port 33 to control the flow rate entering the branch flow channel 110. The provision of a control valve can improve the mass flow rate control capability of the heat exchanger of the present application, and provide good adaptability and flexible operability when applied to specific equipment or systems.

[0059] Optionally, a plurality of branch flow channels 110 are provided on each cold-side heat exchange plate 10 and / or each hot-side heat exchange plate 20 at preset intervals.

[0060] As shown in Figures 4 and 5, the branch flow channels 110 can be arranged at intervals on the first heat exchange flow channel 100 and / or the second heat exchange flow channel 200. Accordingly, in some embodiments, a plurality of branch flow ports 33 distributed at a certain interval are formed on the heat exchange core 1, so that the application parameters of the heat exchanger can be adjusted according to the actual situation, such as the position of convergence or diversion, and the mass flow rate of the working fluid inside the heat exchanger.

[0061] In 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 first heat exchange channels 100 and second heat exchange channels 200 are set in different directions to improve the heat exchange efficiency of the low-temperature working fluid and the high-temperature working fluid through the heat transfer medium (i.e., the plate body of the cold-side heat exchange plate 10 or the hot-side heat exchange plate 20). For example, changing the length and channel shape of the first heat exchange channel 100 and the second heat exchange channel 200 increases the heat exchange area between the low-temperature working fluid and the high-temperature working fluid, and improves the heat exchange efficiency of the low-temperature working fluid and the high-temperature working fluid in the heat exchanger. This application provides the following two implementation methods to achieve this effect:

[0062] As an embodiment, referring to Figures 5, 6, and 7, the partitions are a plurality of parallel long gratings, through which all first heat exchange channels 100 and / or all second heat exchange channels 200 form a continuous straight, zigzag, or circuitous flow channel. 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 continuous long gratings, thereby forming the first heat exchange channel 100 or the second heat exchange channel 200. The flow distance of the working fluid in the zigzag or circuitous (S-shaped) sub-channels is significantly greater than that in the straight-line channel. During the heat exchange process, this facilitates rapid changes in the working fluid temperature within a limited travel distance and avoids the occurrence of pinch points.

[0063] As one embodiment, referring to Figure 8 , the partitions are a plurality of regularly distributed fins, through which all first heat exchange channels 100 and / or all second heat exchange channels 200 form discontinuous channels that flow in the same direction and are interconnected. In this embodiment, independent fin structures are used to form a plurality of sub-channels on the cold-side heat exchange plate 10 or the hot-side heat exchange plate 20 to form the first heat exchange channel 100 or the second heat exchange channel 200. Compared with the previous embodiment, the fin structure (such as a teardrop-shaped fin structure viewed from above) imparts directionality to the channel, while the resulting discontinuous channels interconnect the sub-channels, thereby increasing the heat exchanger's mass flow capacity.

[0064] Optionally, the fin structure also includes wing-shaped fins, diamond-shaped fins, and cylindrical fins.

[0065] In some embodiments, to achieve efficient heat exchange in the heat exchanger, various microstructures such as one-dimensional, two-dimensional, and three-dimensional vortex generators (not shown) that do not affect the backflow blocking function may be installed in the first heat exchange channel 100 and / or the second heat exchange channel 200. These microstructures are conventional structures in the prior art that have a backflow blocking function and are not described in detail here.

[0066] Some other embodiments of the present application also provide a Brayton cycle system, which includes a heat source, a thermoelectric conversion unit, a heat recovery unit, a cooling unit, and a compression unit. The heat source, the thermoelectric conversion unit, the heat recovery unit, the cooling unit, and the compression unit are connected in a cycle in sequence, and the heat recovery unit and the cooling unit include the heat exchanger as described in the above embodiments.

[0067] FIG9 is a schematic diagram of the logical connection of the Brayton cycle system provided in the present application, wherein the regenerative unit includes a regenerator, the cooling unit includes a cooler, and the regenerator and the cooler use the heat exchanger in the aforementioned embodiment.

[0068] In some embodiments, further, the compression unit includes a main compressor and at least one re-compressor, the input end of the main compressor is connected to the hot side outlet 32-b of the cooling unit, and the input end of the re-compressor is connected to the hot side outlet 32-b of the heat recovery unit; the output end of the main compressor is connected to the cold side inlet 31-a of the heat recovery unit, and the output end of the re-compressor is connected to the branch port 33 of the heat recovery unit.

[0069] Specifically, referring to Figure 8, the heat exchanger in the aforementioned embodiment is used as an example for the heat regeneration unit. The circulation connection relationship among the heat regeneration unit, the cooling unit, and the compression unit is as follows: the hot side outlet 32-b of the heat regeneration unit forms two routes through a bypass valve: one route 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, and the output end of the main compressor is connected to the cold side inlet 31-a of the heat regeneration unit to form a cycle; the other route is connected to the input end of the recompressor, and the output end of the recompressor is connected to the branch port 33 of the heat regeneration unit to form another cycle.

[0070] During application, before the high-temperature working fluid enters the cooling unit, it is divided into two paths by the bypass valve, which controllably reduces the mass flow of the high-temperature working fluid entering the cooling unit. Correspondingly, the mass flow of the working fluid compressed by the main compressor and entering the cold side inlet 31-a of the heat recovery unit is also reduced. On the other hand, part of the bypassed high-temperature working fluid enters the re-compressor for compression and cooling, and flows into the heat recovery unit through the branch port 33 of the heat recovery unit. The mass flow of the working fluid on the cold side of the heat recovery unit can be adjusted, thereby increasing the temperature difference between the cold side and the hot side of the heat recovery unit, thereby avoiding the pinch point phenomenon.

[0071] Optionally, the branch valve includes a device that controllably divides the working fluid flow path into several branches, which can adopt devices in the prior art such as regulating valves, stop valves, plug valves, etc. that can realize the control branching function.

[0072] Alternatively, if the heat exchanger used in the regenerator unit has multiple branch ports 33 (i.e., the aforementioned embodiment with multiple branch channels 110), the connection between the compressor output and the branch ports 33 can be split by a bypass valve, with each branch port 33 connected. This, in conjunction with the control valve in the aforementioned embodiment, facilitates the delivery of a corresponding mass flow rate of a working fluid with a different temperature into the regenerator unit as needed. Furthermore, when multiple branch ports 33 are selectively connected and converged, the ratio of the low-temperature to high-temperature regenerator sections can be adjusted accordingly, further facilitating the elimination of pinch points (see below for a detailed explanation of the principle).

[0073] In some embodiments, based on the above embodiments, temperature monitoring units are respectively provided on the hot side outlet 32-b of the cooling unit and the cold side outlet 31-b of the heat regeneration unit, and the Brayton cycle system also includes a measurement and control unit, which is electrically connected to the control valve on each branch port 33 and the temperature monitoring unit, respectively, and is used to monitor the temperature of the hot side outlet 32-b of the cooling unit, the temperature of the cold side outlet 31-b of the heat regeneration unit, and adjust and control the internal working fluid flow of the cooling unit and the heat regeneration unit.

[0074] This embodiment adds a measurement and control unit to the circulation system and electrically connects it to the control valve pair on the branch port 33 of the heat exchanger in the heat regeneration unit to achieve precise control of the mass flow of the working fluid entering the cold side of the heat regeneration unit in this circulation system, while facilitating operation; in addition, the cold side outlet 31-b of the heat regeneration unit and the hot side outlet 32-b of the cooling unit in this circulation system are provided with a temperature monitoring unit, which is also electrically connected to the measurement and control unit, providing visual data conditions for the measurement and control unit to control the mass flow of the working fluid entering the heat regeneration unit according to the temperature of the working fluid in each section of the circulation system, while enhancing the overall coordination of the circulation system.

[0075] Optionally, the temperature monitoring unit adopts a digital thermocouple, a thermal resistor and an infrared temperature sensor.

[0076] In some embodiments, as shown in FIG10 , the cooling unit in the Brayton cycle system also utilizes the heat exchanger described in the aforementioned embodiment. In contrast to the flow confluence function employed in the regenerative unit, the heat exchanger's branch flow channels 110 in this embodiment serve as diversion channels. Similarly, each branch flow port 33 in the cooling unit is also electrically connected to the measurement and control unit to achieve the same effects as in the aforementioned embodiment, which will not be further described here.

[0077] The following is a further theoretical analysis of the heat exchanger and Brayton cycle system in the aforementioned embodiment to solve the pinch point problem combined with relevant experimental data:

[0078] It is known from formula (2) that the pinch point phenomenon existing in heat exchange equipment is related to the mass flow rate and constant pressure specific heat of different heat working fluids during heat exchange. In thermodynamic theory, constant pressure specific heat is affected by operating parameters such as working fluid temperature and pressure. Further analysis shows that operating parameters such as temperature and pressure are closely related to Brayton cycle system parameters and process design.

[0079] Figure 11 shows comparative data on the variations in the working fluid temperatures and specific heat at constant pressure on the hot and cold sides of a typical existing regenerator at different cold-side pressures. This data indicates that when the hot-side pressure of the regenerator is 7.9 MPa, a pinch point occurs in the cold-side pressure range of 9 to 25 MPa. As the cold-side pressure gradually decreases, the average specific heat at constant pressure of the cold-side working fluid gradually increases, and the amplitude of the variation also increases. When the cold-side pressure of the regenerator is 9 MPa, only the hot-side inlet 32-a section (approximately 1 / 3 of the total heat exchange section) in the regenerator performs heat exchange, while the hot and cold working fluid temperatures in the remaining sections vary gently. This indicates that heat transfer between the hot and cold working fluids has deteriorated, resulting in low heat transfer efficiency and a significant waste of heat exchange area within the regenerator. Therefore, to address the pinch point problem in the regenerator, the working fluid pressure on the cold side of the regenerator should not be too low and should be at least greater than 12 MPa. On the other hand, from the perspective of the thermal efficiency of the circulation system, the greater the cold side pressure of the regenerator (corresponding to the maximum pressure of the system, see the circulation system in Figure 1), the higher the circulation efficiency can be achieved. From the perspective of compressor design (the cold side pressure of the regenerator corresponds to the compressor outlet pressure, see the circulation system in Figure 1), but the higher the outlet pressure means higher manufacturing difficulty and cost. Therefore, for the cold side pressure of the regenerator, combined with the above experimental data, it is necessary to comprehensively consider various factors such as the regenerator pinch point, system circulation efficiency, and compressor manufacturing difficulty, and it is better to determine it to be adjustable in the range of 12 to 25 MPa. As for the hot side pressure of the regenerator (which corresponds to the turbine outlet pressure, see Figure 1), from the perspective of circulation efficiency, the highest circulation efficiency can be achieved near the critical pressure of supercritical carbon dioxide (7.38 MPa).

[0080] Figure 12 shows comparative data on the variations in the cold-side and hot-side working fluid temperatures and specific heat at constant pressure along the reheat cycle for different cold-side working fluid inlet temperatures in a typical conventional reheater. It can be seen that as the reheater cold-side inlet temperature 31-a (corresponding to the compressor outlet temperature, see the cycle system in Figure 1) increases, the pinch point within the reheater gradually shifts toward the hot-side outlet 32-b. When the cold-side working fluid inlet temperature is 60°C, no pinch point occurs within the reheater; at this point, the cold-side working fluid specific heat at constant pressure is consistently greater than that of the hot-side working fluid. Therefore, to eliminate the pinch point in the reheater, it is advisable to rationally select the cold-side working fluid inlet temperature to ensure that the cold-side working fluid specific heat at constant pressure is consistently greater than that of the hot-side working fluid. On the other hand, the cold-side working fluid inlet temperature is limited by the compressor outlet working fluid temperature. Therefore, when improving the Brayton cycle system based on experimental data, it is necessary to comprehensively consider the impact of the compressor's enthalpy rise on the outlet working fluid temperature and maximize the compressor outlet working fluid temperature. At the same time, by comparing Figures 11 and 12, it can be seen that, compared with increasing the working fluid pressure on the cold side of the regenerator, increasing the working fluid inlet temperature on the cold side can more effectively eliminate the regenerator pinch point problem. Therefore, it is advisable to give priority to increasing the temperature of the cold side inlet 31-a to achieve the elimination of the regenerator pinch point.

[0081] To sum up, in the Brayton cycle system proposed in the present application, as an embodiment, the working fluid of the Brayton cycle system is supercritical carbon dioxide, the pressure of the cold side inlet 31-a of the heat recovery unit is 12MPa~25MPa, the pressure of the cold side inlet 31-a of the heat recovery unit is 7.38MPa, and the temperature of the cold side inlet 31-a of the heat recovery unit is greater than 50°C.

[0082] In the Brayton cycle system, after the temperature and pressure parameters are adjusted to the optimal values, if the pinch point problem is still not solved, it is necessary to consider adjusting the mass flow rate of the working fluid in the heat exchange equipment according to formula (2). That is, by reducing the mass flow rate of the working fluid on the cold side of the regenerator to offset the excessive constant pressure specific heat on the cold side, thereby achieving a large change in the temperature of the working fluid along the cold side.

[0083] Figure 13 shows the comparison of parameters of the working fluid along the hot and cold sides of the existing typical regenerator when the cold side flow rate is different. It can be seen that when the working fluid flow rate of the hot and cold sides of the regenerator is the same, even if there is no pinch point phenomenon, the working fluid temperature changes slowly near the outlet 32-b section of the hot side of the regenerator, indicating that the pinch point is likely to appear on the side of the low-temperature heat recovery section (as a device for counter-heat exchange, it must have a low-temperature heat recovery section and a high-temperature heat recovery section), and the heat exchange efficiency is low, and the heat exchange area of ​​the regenerator is not fully utilized. After the working fluid on the cold side of the regenerator is diverted, the heat capacity of the working fluid on the cold side is increased. The temperature change of the working medium on the cold side is significantly increased, the working medium on the cold side achieves a higher outlet temperature, and the overall temperature distribution of the regenerator is more reasonable. The heat exchange efficiency along the regenerator is higher, and the overall heat exchange area is more fully utilized.

[0084] By using the heat exchanger of the present application as the regenerator in the circulation system and merging it in a diverted manner (i.e., in the aforementioned embodiment, it is connected to the branch port 33 through the re-compressor shunt), it is possible to achieve an operation mode in which the low-temperature regenerator section has a high flow rate on the hot side and a low flow rate on the cold side, thereby avoiding the pinch point problem in the low-temperature section of the regenerator. Figure 14 shows the parameter change data along the high-temperature regenerator section and the low-temperature regenerator section of the regenerator (regenerator unit) in the Brayton cycle system provided by the present application. It can be seen that after adopting the diverted design, the pinch point phenomenon in the regenerator has been eliminated, the overall working medium temperature distribution of the regenerator is reasonable, the heat exchanger area of ​​the regenerator is fully utilized, and a higher heat exchange efficiency is achieved.

[0085] It should be noted that the above experimental observation using the heat exchanger as a regenerator (regenerator unit) is only for the convenience of explanation. People in this field can reasonably infer based on relevant principles that the heat exchanger of this application as a cooler (cooling unit) should have similar results, and the relevant data will not be listed here to prove it.

[0086] The above detailed description of the specific implementation methods of the application is intended only as an example, and the present application is not limited to the specific implementation methods described above. For those skilled in the art, any equivalent modifications or substitutions made to the application are also within the scope of the present application. Therefore, equivalent changes, modifications, and improvements made without departing from the spirit and scope of the present application should be included within the scope of the present application.

Claims

1. A heat exchanger based on solving the pinch problem of the thermodynamic cycle, wherein, The heat exchanger includes: A heat exchange core body, which includes a number of cold-side heat exchange plates and a number of hot-side heat exchange plates arranged in an interleaved layer. A first surface of the cold-side heat exchange plate forms a number of first heat exchange channels through a first spacer, and a second surface of the hot-side heat exchange plate facing the first surface forms a number of second heat exchange channels through a second spacer; the cold-side heat exchange plate and / or the hot-side heat exchange plate further includes a branch channel, and the branch channel is arranged along the whole length of all the first heat exchange channels and / or all the second heat exchange channels and communicates with all the first heat exchange channels and / or all the second heat exchange channels to converge or diverge to / from the cold-side heat exchange plate and / or the hot-side heat exchange plate; A cover plate, which is used to seal the heat exchange core body.

2. The heat exchanger according to claim 1, wherein, The heat exchanger further includes a heat exchange interface, and 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 arranged on the side surface of the heat exchange core body. The cold-side inlet and the cold-side outlet are respectively connected to two ends of the first heat exchange channel, the hot-side inlet and the hot-side outlet are respectively connected to two ends of the second heat exchange channel, the cold-side inlet and the hot-side inlet are respectively located on two side surfaces of the heat exchange core body, the cold-side outlet and the hot-side outlet are respectively located on two side surfaces of the heat exchange core body, and the branch port is connected to one end of the branch channel.

3. The heat exchanger according to claim 2, wherein, There are two branch ports, the branch channel transversely penetrates all the first heat exchange channels and / or all the second heat exchange channels, and each end of the branch channel is connected to a branch port.

4. The heat exchanger according to claim 3, wherein, A control valve is arranged on each branch port to control the flow rate entering the branch channel.

5. The heat exchanger according to any one of claims 1 to 4, wherein, A number of branch channels are arranged on each cold-side heat exchange plate and / or each hot-side heat exchange plate at preset intervals.

6. The heat exchanger according to claim 1, wherein, The spacer is a number of parallel long grid plates, and all the first heat exchange channels and / or all the second heat exchange channels form a linear, zigzag or meandering continuous channel through the spacer.

7. The heat exchanger according to claim 1, wherein, The spacer is a number of regularly distributed fins, and all the first heat exchange channels and / or all the second heat exchange channels form a non-continuous channel that is in the same direction and communicates through the spacer.

8. A Brayton cycle system, the Brayton cycle system comprising a heat source, a thermoelectric conversion unit, a regenerative unit, a cooling unit, and a compression unit, the heat source, the thermoelectric conversion unit, the regenerative unit, the cooling unit, and the compression unit being connected in sequence in a cycle, wherein, The regenerative unit and the cooling unit include the heat exchanger according to any one of claims 1 to 7.

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

10. The Brayton cycle system according to claim 9, wherein, Temperature monitoring units are respectively arranged on the hot-side outlet of the cooling unit and the cold-side outlet of the regenerative unit. The Brayton cycle system further includes a measurement and control unit, and the measurement and control unit is electrically connected to the control valve on each branch port and the temperature monitoring unit respectively, and is used to monitor the hot-side outlet temperature of the cooling unit and the cold-side outlet temperature of the regenerative unit and adjust and control the internal working fluid flow rates of the cooling unit and the regenerative unit.

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

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