Structural design and performance optimization method for cross-flow micro-channel heat exchanger

Abstract

A structural design and performance optimization method for a cross-flow micro-channel heat exchanger comprises the following steps: screening micro-channel size, wall thickness, channel middle distance and section shape by establishing a countercurrent single-channel model, and establishing a local model of the cross-flow micro-channel heat exchanger on the basis of optimal structural parameters; the optimization sequence of structural parameters of the cross-flow micro-channel heat exchanger is determined, the structural parameters such as the section shape and the channel size are adjusted, iterative optimization of the heat exchange capacity and uniformity is conducted, and the cross-flow micro-channel heat exchanger core structure with the heat exchange amount and the thermal stress meeting the requirements is obtained. According to the method, the simulation calculation amount of the cross-flow micro-channel heat exchanger in the design and optimization process can be reduced, optimization is carried out aiming at the phenomenon of uneven temperature distribution caused by cross flow of cold fluid and hot fluid, and heat transfer nonuniformity in the cross-flow micro-channel heat exchanger can be effectively weakened.

Description

Technical Field

[0001] The present invention relates to the technical field of heat exchangers, and particularly to a cross-flow microchannel heat exchanger structure design and performance optimization method. Background Art

[0002] Microchannel heat exchangers have the advantages of compact structure, high heat transfer efficiency, small heat transfer temperature difference, strong temperature and pressure resistance, etc., and are widely used in the fields of aerospace, petrochemical industry, nuclear power, refrigeration, etc. In the future, large-scale applications will also be realized in the fields of supercritical carbon dioxide power generation and solar thermal power generation.

[0003] The structure design of microchannel heat exchangers is an important current technical research direction. Due to the setting of the header structure, the core of the microchannel heat exchanger is often designed in a way that the cold and hot fluid channels are arranged vertically and crosswise, as shown in the appendix. This causes uneven heat transfer, with large temperature differences in the fluid in each heat transfer channel, and reduces the overall heat transfer efficiency of the heat exchanger, as shown in the appendix. In a steam generation system composed of cross-flow microchannel heat exchangers, there may even be a phenomenon of premature boiling or drying in some channels, affecting the operation efficiency and safety of the heat exchange system. Therefore, structural optimization is required to reduce the non-uniformity of heat transfer. Figure 1 shown. This causes uneven heat transfer, with large temperature differences in the fluid in each heat transfer channel, and reduces the overall heat transfer efficiency of the heat exchanger, as shown in the appendix. Figure 2 shown. In a steam generation system composed of cross-flow microchannel heat exchangers, there may even be a phenomenon of premature boiling or drying in some channels, affecting the operation efficiency and safety of the heat exchange system. Therefore, structural optimization is required to reduce the non-uniformity of heat transfer.

[0004] The design of microchannel heat exchangers lacks a mature and accurate thermal calculation formula. Using formulas such as the surface heat transfer coefficient of conventional-sized channels will cause large design errors. Usually, flow and heat transfer simulations need to be carried out for the structural optimization design and performance verification of heat exchangers. However, in a cross-flow heat exchanger with perpendicular cold and hot fluid flows, the temperature, flow rate, pressure, etc. parameters in each channel between the same plates are not equal. Therefore, the cross-flow heat exchanger cannot simplify the core model of the heat exchanger into a single-channel model with periodic boundaries like a counter-flow heat exchanger, resulting in a large amount of flow and heat transfer simulation calculations and difficult structural optimization, thereby increasing the design and optimization difficulty of cross-flow heat exchangers. Although there are already many applications of current cross-flow microchannel heat exchangers, there is still a lack of an efficient and convenient structural optimization method. Summary of the Invention

[0005] The present disclosure provides a cross-flow microchannel heat exchanger structure design and performance optimization method, and its design objects include the channel size, channel number, wall thickness, and cross-sectional shapes of the cold-side channel and the hot-side channel in the cross-flow microchannel heat exchanger. This method screens structural parameters by establishing a counter-flow single-channel model; based on the optimal counter-flow microchannel structure, a local model of the cross-flow microchannel heat exchanger is established to further optimize the channel structure and number to improve heat transfer performance and uniformity; the optimization order of the structural parameters of the cross-flow microchannel heat exchanger is determined first to reduce the amount of calculation in iterative optimization.

[0006] This method mainly includes the following steps: S1: Respectively establish three-dimensional structure models of countercurrent microchannels with different microchannel sizes, wall thicknesses, channel center distances, and cross-sectional shapes; S2: Establish flow and heat transfer models of microchannels with different structures and conduct simulation calculations. Using the comprehensive performance evaluation factor, Colburn factor, and surface area density as evaluation indicators, screen out the optimal cold-side and hot-side microchannel structure parameters under countercurrent conditions; S3. Calculate the heat transfer area according to the heat transfer requirement of the heat exchanger : , where is the total heat transfer coefficient of the cold and hot countercurrent microchannels, and is the logarithmic mean temperature difference; Set the heat transfer area margin coefficient , and obtain the heat transfer area of the cross-flow microchannel heat exchanger: ; Based on the heat transfer area and combined with the space requirements, give the number of single-layer channels and the number of plates; S4: Analyze the sensitivity of heat transfer performance and uniformity to structure parameters. According to the degree of sensitivity, sequentially perform iterative adjustment and optimization of the structure parameters of the fixed cross-flow microchannel heat exchanger and conduct simulation verification. When both the heat transfer amount and thermal stress meet the requirements, output the core structure of the cross-flow microchannel heat exchanger.

[0007] Furthermore, the specific steps of step S1 include: Based on space requirements, processing technology, impurity particle size, corrosion allowance, etc., preliminarily determine the ranges of hot-side and cold-side microchannel sizes, channel center distances, and wall thicknesses, and respectively establish three-dimensional models of countercurrent microchannels with different microchannel sizes, wall thicknesses, channel center distances, and cross-sectional shapes. Among them, the flow directions of the cold fluid and the hot fluid are opposite, and the outer wall surface is set as a periodic boundary.

[0008] Furthermore, the calculation formulas of the evaluation indicators in step S2 include: Comprehensive performance factor:

[0009] Among them, the Nusselt number , is the heat transfer coefficient, is the hydraulic diameter of the channel, is the average thermal conductivity of the fluid; the Fanning friction coefficient , is the pressure drop at the inlet and outlet of the channel, is the length of the channel, is the average density of the fluid, is the average velocity of the fluid; is the Nusselt number of the control model, is the Fanning friction factor of the control model; Colburn factor:

[0010] wherein, is the Reynolds number, is the Prandtl number; Surface area density:

[0011] wherein, is the heat transfer area, is the volume of the heat exchanger.

[0012] Furthermore, the step S4 specifically includes: S41. Analyze the sensitivity of the heat transfer performance and uniformity to the structural parameters, and determine the order and direction of the adjustment of the structural parameters in the performance optimization of the cross-flow microchannel heat exchanger; S42. According to the order and direction of the structural parameter optimization obtained in step S41, on the basis of the obtained optimal counter-flow microchannel structure, sequentially adjust the structural parameters in the local three-dimensional model of the cross-flow microchannel heat exchanger, and carry out the flow and heat transfer calculations to screen the microchannel structures with better heat transfer capacity and uniformity meeting the set requirements; S43. Establish a three-dimensional overall model of the single-layer cross-flow microchannel heat exchanger, and verify whether the cross-flow microchannel heat exchanger meets the design requirements through flow and heat transfer simulation; if it does not meet the design requirements, repeat steps S3, S42, and S43 for iterative adjustment and optimization; if it meets the design requirements, conduct a thermal stress analysis; S44. When the maximum thermal stress exceeds the allowable stress of the material, preferentially adjust the number of single-layer channels and the number of channel layers to improve the temperature distribution uniformity, and repeat steps S43 and S44 for verification and iterative optimization; when both the heat transfer amount and the thermal stress meet the requirements, output the core structure of the cross-flow microchannel heat exchanger.

[0013] Furthermore, the step S41 specifically includes: Establish a local three-dimensional model of the cross-flow microchannel heat exchanger, and carry out the flow and heat transfer calculations; further adjust the channel cross-section structural parameters through the orthogonal test or the uniformity test method, analyze the influence laws of each parameter on the heat transfer performance and uniformity, and combine the range analysis or the regression analysis to obtain the sensitivity of the heat transfer performance and uniformity to the structural parameters, and then determine the order and direction of the adjustment of the structural parameters in the performance optimization of the cross-flow microchannel heat exchanger.

[0014] Further, in step S42, the uniformity is evaluated by the non-uniformity as follows:

[0015] wherein, is the temperature or heat transfer coefficient; the smaller the non-uniformity value, the better the uniformity.

[0016] Compared with the prior art, the beneficial effects of the present disclosure are as follows: 1) A complete cross-flow microchannel heat exchanger structure design and performance optimization method is established; 2) By establishing a countercurrent single-channel model to screen the microchannel size, wall thickness, channel center distance, and cross-sectional shape, and based on the optimal structural parameters, a local model of the cross-flow microchannel heat exchanger is established to further adjust the cross-sectional shape, channel size, etc., and optimize the heat transfer capacity and uniformity, reducing the computational resources consumed in the direct screening of the structural parameters of the cross-flow microchannel heat exchanger; 3) The optimization order of the structural parameters of the cross-flow microchannel heat exchanger is determined preferentially, reducing the computational amount increased by parameter adjustment in the iterative optimization of the cross-flow microchannel heat exchanger; 4) Optimization is carried out for the phenomenon of uneven temperature distribution caused by the cross-flow of hot and cold fluids, which can effectively weaken the heat transfer non-uniformity in the cross-flow microchannel heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] By describing the exemplary embodiments of the present disclosure in more detail in conjunction with the drawings, the above and other objects, features, and advantages of the present disclosure will become more obvious. Among them, in the exemplary embodiment mode of the present disclosure, the same reference numerals generally represent the same components.

[0018] Figure 1 is a schematic diagram of the core of the cross-flow microchannel heat exchanger; Figure 2 is the difference in heat transfer coefficient and heat transfer capacity under cross-flow and countercurrent conditions; Figure 3 is the flow chart of the cross-flow microchannel heat exchanger structure design and performance optimization method according to the present disclosure; Figure 4 is a schematic diagram of the optimal design parameters of the countercurrent microchannel; Figure 5 is the water-side outlet temperature and heat transfer amount in the optimization of the structural parameters of the cross-flow microchannel heat exchanger; Figure 6 is the heat transfer non-uniformity in the optimization of the structural parameters of the cross-flow microchannel heat exchanger; Figure 7 is the local model of the countercurrent and cross-flow channel heat exchanger. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] Preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the preferred embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0020] The present disclosure provides a method for the structural design and performance optimization of a cross-flow microchannel heat exchanger. According to an exemplary embodiment of the present disclosure, the process is as shown in the attached Figure 3 figures, and specifically includes the following steps: Step 1: Based on space requirements, processing technology, impurity particle size, corrosion allowance, etc., preliminarily determine the ranges of the hot-side and cold-side microchannel dimensions ( d ), channel center-to-center spacing ( w ), and wall thickness ( δ ), and establish three-dimensional models of counter-flow microchannels with different microchannel dimensions, wall thicknesses, channel center-to-center spacings, and cross-sectional shapes respectively. The flow directions of the cold fluid and the hot fluid are opposite, and the outer wall is set as a periodic boundary.

[0021] Step 2: Use the finite volume method to establish the flow and heat transfer models of microchannels with different structures and perform simulation calculations. Evaluate the comprehensive performance of heat transfer and compactness of the microchannel heat exchanger based on the comprehensive performance evaluation factor ( PEC ), Colburn factor ( ), and surface area density ( ), and screen out the optimal structural parameters such as the cold-side and hot-side microchannel dimensions and wall thicknesses under counter-flow conditions. The calculation formulas are as follows.

[0022] Comprehensive performance factor:

[0023] Among them, the Nusselt number , is the heat transfer coefficient, is the hydraulic diameter of the channel, is the average thermal conductivity of the fluid. The Fanning friction factor , is the pressure drop at the inlet and outlet of the channel, is the channel length, is the average density of the fluid, is the average velocity of the fluid. is the Nusselt number of the control model, is the Fanning friction factor of the control model.

[0024] Colburn factor:

[0025] wherein is the Reynolds number, is the Prandtl number.

[0026] Surface area density:

[0027] wherein is the heat transfer area, is the volume of the heat exchanger.

[0028] Step 3: Calculate the heat transfer area ( ), according to the heat transfer requirement ( ) of the heat exchanger, , wherein is the total heat transfer coefficient of the countercurrent microchannels of the cold and hot fluids, is the logarithmic mean temperature difference. Since the heat exchange capacity of the countercurrent microchannel heat exchanger is stronger than that of the crossflow microchannel heat exchanger with the same area, a heat transfer area margin coefficient ( ) is set, and the heat transfer area ( ) of the crossflow microchannel heat exchanger is obtained, . According to the heat transfer area and combined with the space requirement, the number of single-layer channels ( ) and the number of plates ( ) are given.

[0029] Step 4: Establish a local three-dimensional model of the crossflow microchannel heat exchanger and carry out flow and heat transfer calculations. Further adjust the structural parameters such as the channel cross-sectional shape and size by methods such as orthogonal experiments and uniform experiments, analyze the influence rules of each parameter on the heat transfer performance and uniformity, and obtain the sensitivity of the heat transfer performance and uniformity to the structural parameters by combining range analysis, regression analysis, etc., so as to determine the order and direction of the adjustment of the structural parameters in the performance optimization of the crossflow microchannel heat exchanger. This step is only carried out once in the iterative optimization.

[0030] Step 5: Since the heat transfer performance and uniformity of the crossflow microchannel heat exchanger are worse than those of the countercurrent microchannel heat exchanger with the same structure, on the basis of the optimal design of the countercurrent microchannel heat exchanger, further adjust the channel structure and number of the crossflow microchannel heat exchanger to reduce the differences in heat transfer performance, heat transfer uniformity, etc. between the crossflow and countercurrent conditions, so as to improve the heat exchange capacity. According to the order and direction of the structural parameter optimization obtained in Step 4, on the basis of the obtained optimal countercurrent microchannel structure, sequentially adjust the channel size, cross-sectional shape and number in the local three-dimensional model of the crossflow microchannel heat exchanger, and carry out flow and heat transfer calculations to screen the microchannel structure with strong heat exchange capacity and good uniformity. The uniformity is evaluated by the non-uniformity ( ), ​ For temperature, heat transfer coefficient, etc., the smaller the non-uniformity value, the better the uniformity. Since cross-flow does not cause an increase in the non-uniformity of pressure drop, the pressure drop change caused by cross-flow is not concerned during the optimization process.

[0031] Step 6: Establish a three-dimensional overall model of the single-layer cross-flow microchannel heat exchanger, conduct fluid flow and heat transfer simulations, obtain the heat transfer amounts on the hot and cold sides, outlet temperatures and pressures, etc., and verify whether the cross-flow microchannel heat exchanger meets the design requirements. If it does not meet the design requirements, repeat Step 3 and Step 5. If it meets the design requirements, conduct a thermal stress analysis.

[0032] Step 7: For the overall cross-flow microchannel heat exchanger, due to the non-uniform temperature distribution, there may be a situation where the local maximum thermal stress exceeds the allowable stress. After obtaining the optimal cross-flow heat exchange channel structure through Step 1, Step 2, Step 4, and Step 5, when the maximum thermal stress exceeds the allowable stress of the material, the number of single-layer channels and the number of channel layers are preferentially adjusted to improve the uniformity of temperature distribution, and repeat Step 6 and Step 7; when both the heat transfer amount and thermal stress meet the requirements, output the core structure of the cross-flow microchannel heat exchanger.

[0033] The above Steps 4 to 7 can also be independently used as a performance optimization method for a completed-designed cross-flow microchannel heat exchanger.

[0034] In this embodiment, a complete structural design and performance optimization method for a cross-flow microchannel heat exchanger is established; through establishing a countercurrent single-channel model, preliminary screening of structural parameters such as channel cross-sectional shape, size, center-to-center distance, and wall thickness is carried out, and on the basis of the optimal structural parameters, a local model of the cross-flow microchannel heat exchanger is established, and the channel structure and number are adjusted to optimize the heat transfer performance and uniformity of the cross-flow heat exchanger, reducing the computing resources consumed in the direct screening of the structural parameters of the cross-flow microchannel heat exchanger; determining the optimization sequence of the structural parameters of the cross-flow microchannel heat exchanger, reducing the computational amount increased by parameter adjustment in the iterative optimization of the cross-flow microchannel heat exchanger.

[0035] Application Example A cross-flow microchannel heat exchanger is applied to a solar thermal power generation system, and the channel structure of the heat exchanger is designed according to its operating conditions. The hot-side fluid is molten salt, the inlet temperature is 618.15 K, the pressure is 0.5 MPa, and the mass flow rate is 1.2 kg / s; the cold-side fluid is water, the inlet temperature is 257.70 K, the pressure is 14.7 MPa, and the mass flow rate is 0.214 kg / s.

[0036] Refer to the appendix Figure 3 , and the main steps are as follows: (1)Design the structure of the microchannel heat exchanger based on the processing technology, operating conditions and simulation results.

[0037] Specifically, the microchannels are processed using etching technology or capillary microchannels, and the microchannels are determined to have two structures: rectangular or circular. Considering the situation of impurity particle blockage in the actual operation of the microchannel heat exchanger, combined with the minimum filtration size of the molten salt filter and the etching depth, the minimum size of the molten salt side microchannel is 1 - 2 mm. Considering the corrosion of molten salt and water at high temperatures, the thickness of the solid domain between channels (wall thickness) should not be less than the corrosion allowance for the service life. For a heat exchanger made of 347H metal, the wall thickness of the molten salt side and the water side should be greater than 0.2 mm.

[0038] On this basis, establish a three-dimensional model of a countercurrent single-channel with different structural parameters such as microchannel size and wall thickness, and use ANSYS Fluent software for fluid flow and heat transfer simulation to calculate various comprehensive performance evaluation factors ( PEC ), Colburn factor ( ), and surface area density ( ). Determine that the molten salt side channel is a rectangular channel with a size of 2.5 mm × 1.4 mm and a wall thickness of 0.3 mm; the water side channel is a circular channel with a diameter of 2 mm and a wall thickness of 0.5 mm. The center-to-center distance between the molten salt side and the water side channels is 3.5 mm. The structural parameters of the countercurrent microchannel are shown in Attachment Figure 4 . This structure is the optimal design of the microchannel under countercurrent conditions. Calculate the heat transfer area ( ) of the heat exchanger according to the required heat transfer amount ( ), and based on the heat transfer area margin coefficient ( ) and space requirements, give 40 layers of cold and hot fluid channels for the cross-flow microchannel heat exchanger, and the number of channels in a single layer is 60.

[0039] (2)Determine the optimization sequence of the structural parameters of the cross-flow microchannel heat exchanger based on the fluid flow and heat transfer simulation.

[0040] Specifically, establish a local model of a single-layer cross-flow microchannel heat exchanger. The length and width of the heat exchange core are each 350 mm. The number of channels on the molten salt side and the water side is 10 each. The cross-sectional shapes of the channels on the molten salt side and the water side are circular / rectangular, rectangular / circular, circular / circular, and rectangular / rectangular respectively. The channel sizes are 0.9 times, 1.0 times, and 1.1 times the optimal countercurrent microchannel size. In addition, based on the optimal countercurrent microchannel structure, establish a core model with 8, 10, or 12 channels on both the molten salt side and the water side to explore the influence degree of the channel cross-sectional shape, size, and number on the performance of the cross-flow microchannel heat exchanger. Obtain the total heat transfer amount of the core, the water side outlet temperature, and the heat transfer non-uniformity through fluid flow and heat transfer simulation, and get Attachment Figure 5 and Attachment Figure 6The calculated results shown.

[0041] According to the appendix Figure 5 It can be seen that reducing the channel size helps to increase the water-side outlet temperature and the heat transfer rate. When the channel is reduced from the original size to 0.9 times, the water-side outlet temperature and the heat transfer rate are increased by 0.65 K and 10.03 J / s respectively. When the molten salt side is a rectangular channel, the water-side outlet temperature and the heat transfer rate can be increased, which are increased by 1.64 - 4.10 K and 24.32 - 97.24 J / s respectively compared with the case where the molten salt side is a circular channel. The heat transfer performance is the strongest when both the molten salt side and the water side are rectangular channels. Increasing the number of channels can significantly increase the outlet temperature and the heat transfer rate. When the number of channels is increased from 10 to 12, the water-side outlet temperature and the heat transfer rate are increased by 5.33 K and 70.44 J / s respectively.

[0042] According to the appendix Figure 6 It can be seen that due to the differences in physical properties and inlet parameters between the hot and cold fluids, the variation trends of their heat transfer non-uniformity are different. Increasing the channel size can reduce the heat transfer non-uniformity on the molten salt side, while the non-uniformity on the water side increases from 0.125 to 0.135. The rectangular molten salt channels on the molten salt side and the water side make the heat transfer non-uniformity on the molten salt side increase by 0.010 and 0.039 compared with the circular molten salt channels. The variation of the non-uniformity on the water side is related to the cross-sectional shapes of both sides of the channels. Increasing the number of channels will enhance the non-uniformity of heat transfer, which is more obvious for the molten salt side. When the number of channels is increased from 10 to 12, the non-uniformity on the molten salt side increases by 0.022.

[0043] Generally speaking, the number of channels has the greatest influence on the heat transfer performance of the cross-flow microchannel heat exchanger, the channel size has a relatively small influence on the heat transfer performance, and the rectangular channel is beneficial to improving the heat transfer performance. Therefore, the optimization sequence of the heat exchanger structure is as follows: first, determine that both the molten salt side and the water side are rectangular channels; second, adjust the number of channels so that the heat transfer performance and compactness meet the design requirements; then appropriately reduce the channel size to further improve the heat transfer performance.

[0044] (3) Optimize the structure of the cross-flow microchannel heat exchanger according to the best design of the counter-flow microchannel heat exchanger.

[0045] Establish a local model of a single-layer counter-flow microchannel heat exchanger under the best design, with both the length and width being 1 / 6 of the heat exchanger core. Establish a local model of a single-layer cross-flow microchannel heat exchanger with the same size and structural parameters, and both the length and width are also 1 / 6 of the heat exchanger core, as shown in the appendix Figure 7 shown. Based on these structural parameters, optimize. According to the above steps, the cross-sectional shapes of the channels on both the molten salt side and the water side are selected as rectangular, the adjustment range of the number of single-layer channels is 60 - 70 (select the adjustment range in combination with the space requirements), and the adjustment range of the channel size is 0.7 - 1.0 times.

[0046] Perform flow and heat transfer simulations for each model, and calculate the heat transfer rate ( ), and the heat transfer non-uniformity ( ). Based on the calculation results of the local model of the counterflow microchannel heat exchanger under the optimal design, give the appropriate selection ranges for the heat transfer rate and heat transfer non-uniformity of the local model of the crossflow microchannel heat exchanger. For example, the heat transfer rate ≥ 360 J / s and the heat transfer non-uniformity ≤ 0.15. Screen out the structural parameters that meet the conditions and select the best value among them.

[0047] (4) Establish an overall model of the single-layer crossflow microchannel heat exchanger, and conduct heat transfer analysis and stress analysis to verify the rationality of the design.

[0048] Based on the optimized structural parameters, establish a three-dimensional overall model of the single-layer crossflow microchannel heat exchanger, conduct flow and heat transfer simulations, and obtain the heat transfer rate, as well as the outlet temperatures and pressures on the cold and hot sides, etc. Verify whether the flow and heat transfer performance of the crossflow microchannel heat exchanger meets the design requirements. If the required heat transfer rate design requirement is not met, adjust the heat transfer area margin coefficient ( ), recalculate the number of single-layer channels and the number of channel layers of the crossflow microchannel heat exchanger, and re-optimize the structure of the crossflow microchannel heat exchanger. This step is repeated until the heat transfer rate of the crossflow microchannel heat exchanger meets the design requirements.

[0049] On this basis, conduct thermal stress analysis using the overall model of the single-layer crossflow microchannel heat exchanger. Since the current best structure of the crossflow microchannel heat exchanger has been obtained in the above steps, when the local maximum thermal stress exceeds the allowable stress of the material, first adjust the number of single-layer channels and the number of channel layers to improve the uniformity of the temperature distribution. Re-conduct flow and heat transfer analysis and thermal stress analysis. When both the heat transfer rate and thermal stress meet the requirements, output the core structure of the crossflow microchannel heat exchanger.

[0050] The above technical solutions are only exemplary embodiments of the present invention. For those skilled in the art, based on the disclosed application methods and principles of the present invention, it is very easy to make various types of improvements or deformations, not limited to the methods described in the above specific embodiments of the present invention. Therefore, the above-described manner is only preferred and does not have a restrictive meaning.

Claims

1. A cross-flow microchannel heat exchanger structure design and performance optimization method, characterized in that It includes the following steps: S1: Respectively establish three-dimensional structure models of countercurrent microchannels with different microchannel sizes, wall thicknesses, channel center distances, and cross-sectional shapes; S2: Establish flow and heat transfer models of microchannels with different structures and conduct simulation calculations. Using the comprehensive performance evaluation factor, Colburn factor, and surface area density as evaluation indicators, screen out the optimal structural parameters of the cold-side and hot-side microchannels under countercurrent conditions; S3. Calculate the heat transfer area according to the heat transfer amount of the heat exchanger according to the design requirements : , where is the total heat transfer coefficient of the hot and cold countercurrent microchannels, is the logarithmic mean temperature difference; Set the heat transfer area margin coefficient to obtain the heat transfer area of the cross-flow microchannel heat exchanger as follows: ; According to the heat exchange area Give the number of single-layer channels in combination with space requirements and the number of plates ; S4. Analyze the sensitivity of heat transfer performance and uniformity to structural parameters. According to the degree of sensitivity, iteratively adjust and optimize the structural parameters of the cross-flow microchannel heat exchanger in sequence and conduct simulation verification. When the heat transfer amount and thermal stress both meet the requirements, output the core structure of the cross-flow microchannel heat exchanger.

2. The method according to claim 1, wherein The specific content of step S1 includes: Based on spatial requirements, processing technology, impurity particle size, corrosion allowance, etc., preliminarily determine the ranges of hot-side and cold-side microchannel sizes, channel center distances, and wall thicknesses, and respectively establish three-dimensional models of countercurrent microchannels with different microchannel sizes, wall thicknesses, channel center distances, and cross-sectional shapes. Among them, the flow directions of the cold fluid and the hot fluid are opposite, and the outer wall is set as a periodic boundary.

3. The method according to claim 1, wherein The calculation formulas of the evaluation indicators in step S2 include: Comprehensive performance factor: Among them, the Nusselt number , is the heat transfer coefficient, is the hydraulic diameter of the channel, is the average thermal conductivity of the fluid; the Fanning friction coefficient , is the pressure drop at the inlet and outlet of the channel, is the length of the channel, is the average density of the fluid, is the average velocity of the fluid; is the Nusselt number of the control model, is the Fanning friction coefficient of the control model; Colburn factor: wherein, is the Reynolds number, is the Prandtl number; Surface area density: Among them, is the heat exchange area, is the volume of the heat exchanger.

4. The method according to any one of claims 1 to 3, characterized in that, The specific content of step S4 includes: S41. Analyze the sensitivity of heat transfer performance and uniformity to structural parameters, and determine the order and direction of structural parameter adjustment in the performance optimization of the cross-flow microchannel heat exchanger; S42. According to the order and direction of structural parameter optimization obtained in step S41, on the basis of the obtained optimal countercurrent microchannel structure, sequentially adjust the structural parameters in the local three-dimensional model of the cross-flow microchannel heat exchanger, and conduct flow and heat transfer calculations to screen out microchannel structures with better heat transfer capacity and uniformity meeting the set requirements; S43. Establish a three-dimensional overall model of a single-layer cross-flow microchannel heat exchanger, and verify whether the cross-flow microchannel heat exchanger meets the design requirements through flow and heat transfer simulation; if it does not meet the design requirements, repeat steps S3, S42, and S43 for iterative adjustment and optimization; if it meets the design requirements, conduct thermal stress analysis; S44. When the maximum thermal stress exceeds the allowable stress of the material, the number of single-layer channels is preferentially adjusted and the number of channel layers , so as to improve the temperature distribution uniformity, and repeat steps S43 and S44 for verification and iterative optimization; when both the heat transfer capacity and the thermal stress meet the requirements, output the cross-flow microchannel heat exchanger core structure.

5. The method according to claim 4, characterized in that The specific content of step S41 includes: Establish a local three-dimensional model of the cross-flow microchannel heat exchanger and conduct flow and heat transfer calculations; adjust the channel cross-sectional structural parameters through the orthogonal test or uniformity test method, analyze the influence laws of each parameter on heat transfer performance and uniformity, and combine range analysis or regression analysis to obtain the sensitivity of heat transfer performance and uniformity to structural parameters, and then determine the order and direction of structural parameter adjustment in the performance optimization of the cross-flow microchannel heat exchanger.

6. The method according to claim 4, characterized in that, In the step S42, the uniformity is evaluated by the non-uniformity Evaluation: wherein, is the temperature or heat transfer coefficient; the smaller the non-uniformity value, the better the uniformity.

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