A printed circuit board heat exchanger with variable ratio of hot and cold heat exchange plates and its thermal design method

Abstract

The present invention discloses a printed circuit board type heat exchanger with variable ratio of hot and cold heat exchange plates and its thermal design method. This type of heat exchanger is composed of a periodic heat exchange unit consisting of m layers of hot fluid heat exchange plates and n layers of cold fluid heat exchange plates, where m and n are variable according to specific application scenarios. The method includes: respectively establishing physical models of equivalent fin efficiency on the hot fluid side and the cold fluid side according to the ratio of m and n in the periodic heat exchange unit, dividing the heat exchanger into sub-heat exchangers along the flow direction, and establishing an equivalent flat plate heat conduction model and a working fluid flow heat exchange model for each sub-heat exchanger. Solve the control equations of all sub-heat exchangers by simultaneously taking the temperature field and the pressure field as unknown variables, and determine the independence of the discrete mode of the sub-heat exchanger and the convergent design result that meets the user requirements based on the solved temperature field and pressure field results, and output them. Compared with the conventional computational fluid dynamics calculation method, the calculation amount can be reduced by more than 99.99%, and the same thermal design accuracy can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of heat exchanger design, and in particular to a printed circuit board type heat exchanger with a variable ratio of cold and hot heat exchange plates and a thermal design method thereof. Background Art

[0002] The unique performance of printed circuit board heat exchangers makes them occupy an important position in modern industry and energy fields. Their efficient heat transfer capacity maximizes the heat transfer area and efficiency per unit volume. At the same time, their superior high temperature and high pressure resistance ensure their stability and safety under harsh working conditions. For example, in the supercritical carbon dioxide power cycle, the heat exchanger can perfectly cope with high temperatures above 800K and high pressure operating environments of 20MPa, demonstrating excellent engineering adaptability. In addition, due to the extremely drastic changes in the physical properties of supercritical carbon dioxide in the quasi-critical region (such as significant fluctuations in density and specific heat), advanced heat exchanger designs have shown great potential in optimizing fluid flow characteristics, improving heat transfer efficiency and reducing pressure drop. This customized and refined design approach can effectively improve the operating efficiency of equipment in fields such as energy, petrochemicals, refrigeration and advanced nuclear energy, and provides a new solution for the development of thermal hydraulic performance.

[0003] In industrial applications, to match the requirements for hot and cold side working fluid flow, heat exchange, and pressure drop, one method for printed circuit board heat exchangers is to employ a core arrangement with a variable hot and cold plate ratio, consisting of a periodic heat exchange unit composed of several layers (m layers) of heat exchange plates for heat supply fluid flow and several layers (n layers) of heat exchange plates for cold supply fluid flow. Due to the significant structural differences between printed circuit board heat exchangers with a variable hot and cold plate ratio and traditional printed circuit board heat exchangers with a single hot plate and single cold plate arrangement, such as the large number of flow channels and complex structure, it is difficult to directly employ existing thermal design methods developed for printed circuit board heat exchangers with a single hot plate and single cold plate arrangement. Using computational fluid dynamics methods for the thermal design of printed circuit board heat exchangers with a variable hot and cold plate ratio requires enormous computing resources and suffers from low computational efficiency. Summary of the Invention

[0004] The present invention aims to address the shortcomings of the prior art and provide a printed circuit board type heat exchanger with a variable ratio of hot and cold heat exchange plates, which adopts the concept of equivalent fin efficiency, and a thermal design method thereof. This technical solution can perform thermal design on a printed circuit board type heat exchanger with a variable ratio of hot and cold heat exchange plates while ensuring calculation accuracy and high efficiency.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] In a first aspect, a thermal design method for a printed circuit board type heat exchanger with a variable ratio of hot and cold heat exchange plates is provided, characterized in that it comprises the following steps:

[0007] Step 1: Based on the estimated ratio of the hot fluid heat exchange plate and the cold fluid heat exchange plate in the periodic heat exchange unit and the geometric parameters of the heat exchange plate flow channel, establish the equivalent fin efficiency physical model of the hot fluid side and the cold fluid side respectively;

[0008] Step 2: Divide the heat exchanger into sub-heat exchangers along the fluid flow direction, and establish a flow and heat transfer model between the hot fluid and the cold fluid for each sub-heat exchanger;

[0009] Step 3: Using the temperature field and pressure field as unknown variables, solve the control equations of all sub-heat exchangers simultaneously. Based on the solved temperature and pressure field results, determine whether the sub-heat exchangers comply with the discrete mode independence and whether they meet the user's requirements for heat load and pressure drop. If not, adjust the geometric parameters of the heat exchanger flow channel and return to step 1. If yes, output the design results of the heat exchanger.

[0010] Furthermore, in step 1, the physical model of equivalent fin efficiency is:

[0011]

[0012] Among them, η f1 is the fin efficiency on the hot fluid side; h1 is the convection heat transfer coefficient of the fin surface on the hot fluid side; λ1 is the thermal conductivity of the solid area of the fin on the hot fluid side; H1 is the fin height on the hot fluid side; δ1 is the fin thickness on the hot fluid side; D1 is the diameter of the semicircular flow channel on the hot fluid side; t1 is the distance between the bottom of the semicircular flow channel on the hot fluid side and the surface of the heat exchange plate; m is the number of heat exchange plate layers on the hot fluid side; f1 is the distance between the semicircular flow channels of the heat exchange plate on the hot fluid side; η f2 is the fin efficiency on the cold fluid side; h2 is the convective heat transfer coefficient of the fin surface on the cold fluid side; λ2 is the thermal conductivity of the solid area of the fin on the cold fluid side; H2 is the fin height on the cold fluid side; δ2 is the fin thickness on the cold fluid side; D2 is the diameter of the semicircular flow channel on the cold fluid side; t2 is the distance between the bottom of the semicircular flow channel on the cold fluid side and the surface of the heat exchange plate; n is the number of heat exchange plate layers on the cold fluid side; f2 is the distance between the semicircular flow channels of the heat exchange plate on the hot fluid side.

[0013] Furthermore, in step 2, the sub-heat exchanger is divided into N parts, and the flow heat transfer model between the hot fluid and the cold fluid in the i-th sub-heat exchanger is:

[0014]

[0015] Among them, Q i is the heat transfer between the hot fluid and the cold fluid in the i-th sub-heat exchanger; U i A is the total heat transfer coefficient between the hot fluid and the cold fluid in the i-th sub-heat exchanger;i,1 is the total heat transfer area on the hot fluid side in the i-th sub-heat exchanger; T i,1 is the mainstream temperature of the hot fluid side in the i-th sub-heat exchanger; T i,2 is the mainstream temperature of the cold fluid side in the i-th sub-heat exchanger; h i,1 is the convective heat transfer coefficient on the hot fluid side in the i-th sub-heat exchanger; A i,1,0 is the primary heat transfer area on the hot fluid side in the i-th sub-heat exchanger; A i,1,1 is the secondary heat transfer area on the hot fluid side in the i-th sub-heat exchanger; η i,f1 is the fin efficiency on the hot fluid side in the i-th sub-heat exchanger; k i,s is the thermal conductivity of the solid region in the i-th sub-heat exchanger; t i,1 is the distance between the bottom of the semi-circular flow channel on the hot fluid side and the heat transfer plate surface in the i-th sub-heat exchanger; t i,2 is the distance between the bottom of the semi-circular flow channel on the cold fluid side and the heat transfer plate surface in the i-th sub-heat exchanger; A i,s is the heat conduction cross-sectional area between the hot and cold fluids in the i-th sub-heat exchanger; h i,2 is the convective heat transfer coefficient on the cold fluid side in the i-th sub-heat exchanger; A i,2,0 is the primary heat transfer area on the cold fluid side in the i-th sub-heat exchanger; A i,2,1 is the secondary heat transfer area on the cold fluid side in the i-th sub-heat exchanger; η i,f2 is the fin efficiency on the cold fluid side in the i-th sub-heat exchanger.

[0016] Furthermore, in step three, the temperature field equations of the i-th sub-heat exchanger are as follows:

[0017] m i,1 Cp i,1 (T i,1,out -T i,1,in ) = U i A i,1 (T i,1 -T i,2 )

[0018] m i,2 Cp i,2 (T i,2,out -T i,2,in ) = U i A i,1 (T i,1 -T i,2 )

[0019] Among them, m i,1 is the mass flow rate of the hot fluid in the i-th sub-heat exchanger; Cp i,1 is the specific heat capacity at constant pressure of the hot fluid in the i-th sub-heat exchanger; T i,1,out is the outlet temperature of the hot fluid in the i-th sub-heat exchanger; T i,1,inis the inlet temperature of the hot fluid in the i-th sub-heat exchanger; m i,2 is the mass flow rate of the cold fluid in the i-th sub-heat exchanger; Cp i,2 is the specific heat capacity at constant pressure of the cold fluid in the i-th sub-heat exchanger; T i,2,out is the outlet temperature of the cold fluid in the i-th sub-heat exchanger; T i,2,in is the inlet temperature of the cold fluid in the i-th sub-heat exchanger;

[0020] The temperature field equations are solved by using the principal element Gaussian elimination method, and the pressure field is calculated based on the obtained temperature field. The pressure field formulas for the hot fluid and the cold fluid in the i-th sub-heat exchanger are as follows:

[0021]

[0022] where, Δp i is the total pressure drop of the hot fluid or the cold fluid in the i-th sub-heat exchanger; λ i is the friction resistance coefficient of the hot fluid or the cold fluid in the i-th sub-heat exchanger; ξ i is the total local resistance coefficient of the hot fluid or the cold fluid in the i-th sub-heat exchanger; l i is the flow length of the hot fluid or the cold fluid in the i-th sub-heat exchanger; D i,eq is the equivalent hydraulic diameter of the hot fluid or the cold fluid in the i-th sub-heat exchanger; G i is the mass velocity of the hot fluid or the cold fluid in the i-th sub-heat exchanger; ρ i,out is the outlet density of the hot fluid or the cold fluid in the i-th sub-heat exchanger; ρ i,in is the inlet density of the hot fluid or the cold fluid in the i-th sub-heat exchanger; Δp i,gravity is the hydrostatic pressure drop of the hot fluid or the cold fluid in the i-th sub-heat exchanger;

[0023] Update the physical properties according to the solved pressure field, and calculate the temperature field again. Iterate in this way until the deviation between the results of the previous and the current calculations meets the requirements of the user and the independence requirement of the discretization method. Then stop the iteration and output the final geometric parameter design results of the converged heat exchange plate flow channel.

[0024] In the second aspect, a printed circuit board type heat exchanger with a variable ratio of hot and cold heat exchange plates is provided, which is characterized in that it is designed using the method described in the first aspect, and includes a heat exchanger core, an upper cover plate, a lower cover plate, a hot fluid inlet pipe, a hot fluid outlet pipe, a cold fluid inlet pipe, and a cold fluid outlet pipe. The heat exchanger core includes hot fluid heat exchange plates and cold fluid heat exchange plates, and the hot fluid heat exchange plates and cold fluid heat exchange plates are alternately stacked according to a certain ratio. The upper cover plate and the lower cover plate are respectively arranged at the upper and lower ends of the heat exchanger core, and hot fluid flow channels are arranged on the hot fluid heat exchange plates, and cold fluid flow channels are arranged on the cold fluid heat exchange plates. The hot fluid inlet pipe and the hot fluid outlet pipe are respectively connected to the hot fluid flow channel inlet end and the hot fluid flow channel outlet end, and the cold fluid inlet pipe and the cold fluid outlet pipe are respectively connected to the cold fluid flow channel inlet end and the cold fluid flow channel outlet end.

[0025] Furthermore, the ratio of the hot fluid heat exchange plate to the cold fluid heat exchange plate is (1-10):(1-10).

[0026] Furthermore, the hot fluid flow channel and the cold fluid flow channel are arranged in countercurrent, the hot fluid flow channel inlet end and the cold fluid flow channel outlet end are located on the same side of the heat exchanger core, and the hot fluid flow channel outlet end and the cold fluid flow channel inlet end are located on the same side of the heat exchanger core.

[0027] Furthermore, the hot fluid inlet pipe and the cold fluid outlet pipe are arranged at intervals, and the hot fluid outlet pipe and the cold fluid inlet pipe are arranged at intervals.

[0028] Furthermore, the hot fluid flow channel and the cold fluid flow channel are straight flow channels or broken line flow channels.

[0029] Furthermore, the cross-sections of the hot fluid flow channel and the cold fluid flow channel are semicircular.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention relates to a thermal design method for a printed circuit board type heat exchanger with a variable ratio of cold and hot heat exchanger plates. The heat transfer model is established based on the equivalent fin efficiency concept. The heat exchanger is spatially discretized to form a number of sub-heat exchangers. Model equations are established for the discretized sub-heat exchangers. Then, all the sub-heat exchanger equations are solved and calculated together. This avoids direct modeling and meshing of the heat exchanger composed of hundreds of thousands of micro channels, greatly reduces the difficulty of modeling and the number of meshes. Compared with conventional computational fluid dynamics calculation methods, the amount of calculation can be reduced by more than 99.99%, and the same thermal design accuracy can be achieved.

[0032] (2) The equivalent fin efficiency processing method of the present invention fully considers the heat transfer efficiency problems of each heat transfer surface in a periodic heat exchange unit composed of several layers (m layers) of heat exchange plates for the flow and heat exchange of working fluid one and several layers (n layers) of heat exchange plates for the flow and heat exchange of working fluid two. Compared with the traditional heat design method of a printed circuit board heat exchanger with a one-layer hot plate and one-layer cold plate arrangement, the heat design error can be reduced from 25% to within 5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 FIG. is a flow chart of the heat design method for the heat exchanger in Embodiment 1;

[0034] Figure 2 FIG. is a partial cross-sectional view of the hot fluid heat exchange plate and the cold fluid heat exchange plate in Embodiment 1;

[0035] Figure 3 FIG. is a comparison diagram of the temperature distributions on the hot and cold sides of the heat exchanger designed by the method in Embodiment 1 and the calculation results by the computational fluid dynamics method;

[0036] Figure 4 FIG. is a schematic structural diagram of a printed circuit board heat exchanger with variable ratio of hot and cold heat exchange plates in Embodiment 2;

[0037] Figure 5 FIG. is a schematic structural diagram of the hot fluid heat exchange plate in Embodiment 2;

[0038] Figure 6 FIG. is a schematic structural diagram of the cold fluid heat exchange plate in Embodiment 2;

[0039] Wherein: 1 - upper cover plate, 2 - lower cover plate, 3 - hot fluid inlet nozzle, 4 - hot fluid outlet nozzle, 5 - cold fluid inlet nozzle, 6 - cold fluid outlet nozzle, 7 - hot fluid heat exchange plate, 8 - cold fluid heat exchange plate, 9 - hot fluid flow channel, 10 - cold fluid flow channel, 11 - hot fluid flow channel inlet end, 12 - hot fluid flow channel outlet end, 13 - cold fluid flow channel inlet end, 14 - cold fluid flow channel outlet end. DETAILED DESCRIPTION OF THE INVENTION

[0040] To deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings. This embodiment is only used to explain the present invention and does not constitute a limitation to the protection scope of the present invention.

[0041] Embodiment 1

[0042] As Figure 1 shown, a specific embodiment of the heat design method of a printed circuit board heat exchanger with variable ratio of hot and cold heat exchange plates includes the following steps:

[0043] Step 1: As Figure 2As shown in the figure, according to the ratio of the three layers of hot fluid heat exchange plates and the two layers of cold fluid heat exchange plates in the estimated periodic heat exchange unit and the geometric parameters of the heat exchange plate flow channels, physical models of the equivalent fin efficiency on the hot fluid side and the cold fluid side are respectively established.

[0044]

[0045]

[0046] Among them, η f1 is the fin efficiency on the hot fluid side; h1 is the convective heat transfer coefficient on the surface of the fins on the hot fluid side; λ1 is the thermal conductivity of the solid region of the fins on the hot fluid side; H1 is the height of the fins on the hot fluid side; δ1 is the thickness of the fins on the hot fluid side; D1 is the diameter of the semi-circular flow channel on the hot fluid side; t1 is the distance between the bottom of the semi-circular flow channel on the hot fluid side and the surface of the heat exchange plate; m is the number of layers of the hot fluid side heat exchange plates; f1 is the distance between the semi-circular flow channels of the hot fluid side heat exchange plates; η f2 is the fin efficiency on the cold fluid side; h2 is the convective heat transfer coefficient on the surface of the fins on the cold fluid side; λ2 is the thermal conductivity of the solid region of the fins on the cold fluid side; H2 is the height of the fins on the cold fluid side; δ2 is the thickness of the fins on the cold fluid side; D2 is the diameter of the semi-circular flow channel on the cold fluid side; t2 is the distance between the bottom of the semi-circular flow channel on the cold fluid side and the surface of the heat exchange plate; n is the number of layers of the cold fluid side heat exchange plates; f2 is the distance between the semi-circular flow channels of the hot fluid side heat exchange plates.

[0047] Step 2: Divide the heat exchanger into sub-heat exchangers along the fluid flow direction, and establish a flow and heat transfer model between the hot fluid and the cold fluid for each sub-heat exchanger.

[0048]

[0049] Among them, Q i is the heat transfer amount between the hot fluid and the cold fluid in the i-th sub-heat exchanger; U i is the total heat transfer coefficient between the hot fluid and the cold fluid in the i-th sub-heat exchanger; A i,1 is the total heat transfer area on the hot fluid side in the i-th sub-heat exchanger; T i,1 is the mainstream temperature on the hot fluid side in the i-th sub-heat exchanger; T i,2 is the mainstream temperature on the cold fluid side in the i-th sub-heat exchanger; h i,1 is the convective heat transfer coefficient on the hot fluid side in the i-th sub-heat exchanger; A i,1,0 is the primary heat transfer area on the hot fluid side in the i-th sub-heat exchanger; A i,1,1 is the secondary heat transfer area on the hot fluid side in the i-th sub-heat exchanger; η i,f1 is the fin efficiency on the hot fluid side in the i-th sub-heat exchanger; k i,s is the thermal conductivity of the solid region in the i-th sub-heat exchanger; t i,1is the distance between the bottom of the semi-circular flow channel on the hot fluid side and the heat transfer plate surface in the i-th sub-heat exchanger; t i,2 is the distance between the bottom of the semi-circular flow channel on the cold fluid side and the heat transfer plate surface in the i-th sub-heat exchanger; A i,s is the heat conduction cross-sectional area between the hot and cold fluids in the i-th sub-heat exchanger; h i,2 is the convective heat transfer coefficient on the cold fluid side in the i-th sub-heat exchanger; A i,2,0 is the primary heat transfer area on the cold fluid side in the i-th sub-heat exchanger; A i,2,1 is the secondary heat transfer area on the cold fluid side in the i-th sub-heat exchanger; η i,f2 is the fin efficiency on the cold fluid side in the i-th sub-heat exchanger.

[0050] Step 3: Taking the temperature field and pressure field as unknown variables, simultaneously solve the control equations of all sub-heat exchangers. The temperature field equation set of the i-th sub-heat exchanger is:

[0051] m i,1 Cp i,1 (T i,1,out -T i,1,in ) = U i A i,1 (T i,1 -T i,2 )

[0052] m i,2 Cp i,2 (T i,2,out -T i,2,in s) = U i A i,1 (T i,1 -T i,2 )

[0053] Among them, m i,1 is the mass flow rate of the hot fluid in the i-th sub-heat exchanger; Cp i,1 is the specific heat capacity at constant pressure of the hot fluid in the i-th sub-heat exchanger; T i,1,out is the outlet temperature of the hot fluid in the i-th sub-heat exchanger; T i,1,in is the inlet temperature of the hot fluid in the i-th sub-heat exchanger; m i,2 is the mass flow rate of the cold fluid in the i-th sub-heat exchanger; Cp i,2 is the specific heat capacity at constant pressure of the cold fluid in the i-th sub-heat exchanger; T i,2,out is the outlet temperature of the cold fluid in the i-th sub-heat exchanger; T i,2,in is the inlet temperature of the cold fluid in the i-th sub-heat exchanger;

[0054] Use the principal element Gaussian elimination method to solve the temperature field equation set, and calculate the pressure field based on the obtained temperature field. The pressure field formulas of the hot and cold fluids in the i-th sub-heat exchanger are:

[0055]

[0056] where, Δp i is the total pressure drop of the hot fluid or cold fluid in the i-th sub-heat exchanger; λ i is the friction resistance coefficient of the hot fluid or cold fluid in the i-th sub-heat exchanger; ξ i is the total local resistance coefficient of the hot fluid or cold fluid in the i-th sub-heat exchanger; l i is the flow length of the hot fluid or cold fluid in the i-th sub-heat exchanger; D i,eq is the equivalent hydraulic diameter of the hot fluid or cold fluid in the i-th sub-heat exchanger; G i is the mass flow rate of the hot fluid or cold fluid in the i-th sub-heat exchanger; ρ i,out is the outlet density of the hot fluid or cold fluid in the i-th sub-heat exchanger; ρ i,in is the inlet density of the hot fluid or cold fluid in the i-th sub-heat exchanger; Δp i,gravity is the hydrostatic pressure drop of the hot fluid or cold fluid in the i-th sub-heat exchanger. Update the geometric parameters of the heat exchange plate flow channel according to the solved pressure field, and calculate the temperature field again. Iterate in this way until the deviation between the calculation results of the previous and the next time meets the requirements of the user and the independence requirement of the discretization method, stop the iteration, and output the final heat exchanger convergence design result.

[0057] Given the conditions of the cold fluid side inlet temperature of 298K, pressure of 0.1MPa, air flow rate of 5m / s, and the hot fluid side inlet temperature of 373K, pressure of 0.1MPa, air flow rate of 5m / s, a printed circuit board heat exchanger composed of 3 layers of hot fluid heat exchange plates and 2 layers of cold fluid heat exchange plates as the periodic heat transfer unit is designed by the above method. D1 and D2 are 2mm, f1 and f2 are 0.2mm, t1 and t2 are 0.5mm. To achieve the required heat transfer amount, the lengths required for the hot fluid flow channel and the cold fluid flow channel are 149mm. The temperature distributions on the hot and cold sides of this heat exchanger are compared with the calculation results of the computational fluid dynamics method as Figure 6 shown. The calculation time required by the thermal design method of the present invention is less than 0.1 second, and the operating memory is less than 1MB. While the computational fluid dynamics method requires 10 hours and 500MB of memory. The calculation time is shortened by more than 99.9% compared with the computational fluid dynamics method, the calculation resources are reduced to 1 / 500, and the calculation accuracy of the fluid temperature is greater than 98%.

[0058] Embodiment 2

[0059] As Figures 4 - 6As shown in the figure, a printed circuit board heat exchanger with a variable ratio of hot and cold heat exchange plates is designed by the method in Embodiment 1, and includes a heat exchanger core body, an upper cover plate 1, a lower cover plate 2, a hot fluid inlet connecting pipe 3, a hot fluid outlet connecting pipe 4, a cold fluid inlet connecting pipe 5, and a cold fluid outlet connecting pipe 6. The heat exchanger core body includes a hot fluid heat exchange plate 7 and a cold fluid heat exchange plate 8. The hot fluid heat exchange plate 7 and the cold fluid heat exchange plate 8 are alternately stacked and arranged according to a ratio of 2:4. The upper cover plate 1 and the lower cover plate 2 are respectively arranged at the upper end and the lower end of the heat exchanger core body. A hot fluid flow channel 9 is arranged on the hot fluid heat exchange plate 7, and a cold fluid flow channel 10 is arranged on the cold fluid heat exchange plate 8. The hot fluid inlet connecting pipe 3 and the hot fluid outlet connecting pipe 4 are respectively communicated with the inlet end 11 and the outlet end 12 of the hot fluid flow channel. The cold fluid inlet connecting pipe 5 and the cold fluid outlet connecting pipe 6 are respectively connected to the inlet end 13 and the outlet end 14 of the cold fluid flow channel.

[0060] The hot fluid flow channel 9 and the cold fluid flow channel 10 are arranged in a countercurrent manner. The inlet end 11 of the hot fluid flow channel and the outlet end 14 of the cold fluid flow channel are located on the same side of the heat exchanger core body. The outlet end 12 of the hot fluid flow channel and the inlet end 13 of the cold fluid flow channel are located on the same side of the heat exchanger core body. The hot fluid inlet connecting pipe 3 and the cold fluid outlet connecting pipe 6 are arranged at intervals. The hot fluid outlet connecting pipe 4 and the cold fluid inlet connecting pipe 5 are arranged at intervals. The hot fluid flow channel 9 and the cold fluid flow channel 10 are straight channels. The cross-sections of the hot fluid flow channel 9 and the cold fluid flow channel 10 are semi-circular.

[0061] The above specific implementation manners are only for explaining the technical concept and structural features of the present invention, and are intended to enable those skilled in the art to implement it accordingly. However, the above content does not limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A thermal design method for a printed circuit board heat exchanger with variable ratio of hot and cold heat exchange plates, characterized in that The following steps are involved: Step 1: Based on the estimated ratio of the hot fluid heat exchange plate and the cold fluid heat exchange plate in the periodic heat exchange unit and the geometric parameters of the heat exchange plate flow channel, establish the equivalent fin efficiency physical model of the hot fluid side and the cold fluid side respectively. The equivalent fin efficiency physical model is: where η f1 is the fin efficiency on the hot fluid side; h1 is the convective heat transfer coefficient on the surface of the fins on the hot fluid side; λ1 is the thermal conductivity of the solid region of the fins on the hot fluid side; H1 is the height of the fins on the hot fluid side; δ1 is the thickness of the fins on the hot fluid side; D1 is the diameter of the semi-circular flow channel on the hot fluid side; t1 is the distance between the bottom of the semi-circular flow channel on the hot fluid side and the surface of the heat exchange plate; m is the number of heat exchange plates on the hot fluid side; f1 is the distance between the semi-circular flow channels of the heat exchange plate on the hot fluid side; η f2 is the fin efficiency on the cold fluid side; h2 is the convective heat transfer coefficient on the surface of the fins on the cold fluid side; λ2 is the thermal conductivity of the solid region of the fins on the cold fluid side; H2 is the height of the fins on the cold fluid side; δ2 is the thickness of the fins on the cold fluid side; D2 is the diameter of the semi-circular flow channel on the cold fluid side; t2 is the distance between the bottom of the semi-circular flow channel on the cold fluid side and the surface of the heat exchange plate; n is the number of heat exchange plates on the cold fluid side; f2 is the distance between the semi-circular flow channels of the heat exchange plate on the hot fluid side; Step 2: Divide the heat exchanger into sub-heat exchangers along the fluid flow direction, and establish a flow and heat transfer model between the hot fluid and the cold fluid for each sub-heat exchanger; Step 3: Using the temperature field and pressure field as unknown variables, solve the control equations of all sub-heat exchangers simultaneously. Based on the solved temperature and pressure field results, determine whether the sub-heat exchangers comply with the discrete mode independence and whether they meet the user's requirements for heat load and pressure drop. If not, adjust the geometric parameters of the heat exchanger flow channel and return to step 1. If yes, output the design results of the heat exchanger.

2. The thermal design method of a printed circuit board type heat exchanger with variable ratio of hot and cold heat exchange plates according to claim 1, characterized in that, In step 2, the sub-heat exchanger is divided into N parts, and the flow heat transfer model between the hot fluid and the cold fluid in the i-th sub-heat exchanger is: Q i = U i A i,1 (T i,1 - T i,2 ) Among them, Q i is the heat transfer amount between the hot fluid and the cold fluid in the i-th sub-heat exchanger; U i is the overall heat transfer coefficient between the hot fluid and the cold fluid in the i-th sub-heat exchanger; A i,1 is the total heat transfer area on the hot fluid side in the i-th sub-heat exchanger; T i,1 is the mainstream temperature on the hot fluid side in the i-th sub-heat exchanger; T i,2 is the mainstream temperature on the cold fluid side in the i-th sub-heat exchanger; h i,1 is the convective heat transfer coefficient on the hot fluid side in the i-th sub-heat exchanger; A i,1,0 is the primary heat transfer area on the hot fluid side in the i-th sub-heat exchanger; A i,1,1 is the secondary heat transfer area on the hot fluid side in the i-th sub-heat exchanger; η i,f1 is the fin efficiency on the hot fluid side in the i-th sub-heat exchanger; k i,s is the thermal conductivity of the solid region in the i-th sub-heat exchanger; t i,1 is the distance between the bottom of the semi-circular flow channel on the hot fluid side and the heat transfer plate surface in the i-th sub-heat exchanger; t i,2 is the distance between the bottom of the semi-circular flow channel on the cold fluid side and the heat transfer plate surface in the i-th sub-heat exchanger; A i,s is the heat conduction cross-sectional area between the hot fluid and the cold fluid in the i-th sub-heat exchanger; h i,2 is the convective heat transfer coefficient on the cold fluid side in the i-th sub-heat exchanger; A i,2,0 is the primary heat transfer area on the cold fluid side in the i-th sub-heat exchanger; A i,2,1 is the secondary heat transfer area on the cold fluid side in the i-th sub-heat exchanger; η i,f2 is the fin efficiency on the cold fluid side in the i-th sub-heat exchanger.

3. The thermal design method of a printed circuit board type heat exchanger with variable ratio of hot and cold heat exchange plates according to claim 2, characterized in that In step 3, the temperature field equations of the i-th sub-heat exchanger are: m i,1 Cp i,1 (T i,1,out -T i,1,in )=U i A i,1 (T i,1 -T i,2 ) m i,2 Cp i,2 (T i,2,out -T i,2,in )=U i A i,1 (T i,1 -T i,2 ) where m i,1 is the mass flow rate of the hot fluid in the i-th sub-heat exchanger; Cp i,1 is the specific heat capacity at constant pressure of the hot fluid in the i-th sub-heat exchanger; T i,1,out is the outlet temperature of the hot fluid in the i-th sub-heat exchanger; T i,1,in is the inlet temperature of the hot fluid in the i-th sub-heat exchanger; m i,2 is the mass flow rate of the cold fluid in the i-th sub-heat exchanger; Cp i,2 is the specific heat capacity at constant pressure of the cold fluid in the i-th sub-heat exchanger; T i,2,out is the outlet temperature of the cold fluid in the i-th sub-heat exchanger; T i,2,in is the inlet temperature of the cold fluid in the i-th sub-heat exchanger; The temperature field equations are solved by the principal component Gaussian elimination method, and the pressure field is calculated based on the obtained temperature field. The pressure field formulas of the hot fluid and the cold fluid in the i-th sub-heat exchanger are: Among them, Δp i is the total pressure drop of the hot fluid or cold fluid in the i-th sub-heat exchanger; λ i is the friction resistance coefficient of the hot fluid or cold fluid in the i-th sub-heat exchanger; ξ i is the total local resistance coefficient of the hot fluid or cold fluid in the i-th sub-heat exchanger; l i is the flow length of the hot fluid or cold fluid in the i-th sub-heat exchanger; D i,eq is the equivalent hydraulic diameter of the hot fluid or cold fluid in the i-th sub-heat exchanger; G i is the mass flow rate of the hot fluid or cold fluid in the i-th sub-heat exchanger; ρ i,out is the outlet density of the hot fluid or cold fluid in the i-th sub-heat exchanger; ρ i,in is the inlet density of the hot fluid or cold fluid in the i-th sub-heat exchanger; Δp i,gravity is the hydrostatic head pressure drop of the hot fluid or cold fluid in the i-th sub-heat exchanger; The physical properties are updated based on the solved pressure field, and the temperature field is calculated again. This iteration is repeated until the deviation between the two calculation results meets the user requirements and the independence requirements of the discrete method. The iteration is stopped and the final convergent geometric parameter design results of the heat exchanger flow channel are output.

4. A printed circuit board heat exchanger with variable ratio of hot and cold heat exchange plates, characterized in that The method according to any one of claims 1 to 3 is used for design, comprising a heat exchanger core, an upper cover plate (1), a lower cover plate (2), a hot fluid inlet pipe (3), a hot fluid outlet pipe (4), a cold fluid inlet pipe (5), and a cold fluid outlet pipe (6), wherein the heat exchanger core comprises a hot fluid heat exchange plate (7) and a cold fluid heat exchange plate (8), wherein the hot fluid heat exchange plate (7) and the cold fluid heat exchange plate (8) are alternately stacked in a certain ratio, and the upper cover plate (1) and the lower cover plate (2) are respectively The hot fluid flow channel (9) is arranged at the upper end and the lower end of the heat exchanger core, and the hot fluid heat exchange plate (7) is provided with a hot fluid flow channel (9), and the cold fluid heat exchange plate (8) is provided with a cold fluid flow channel (10). The hot fluid inlet pipe (3) and the hot fluid outlet pipe (4) are respectively connected to the hot fluid flow channel inlet end (11) and the hot fluid flow channel outlet end (12), and the cold fluid inlet pipe (5) and the cold fluid outlet pipe (6) are respectively connected to the cold fluid flow channel inlet end (13) and the cold fluid flow channel outlet end (14).

5. The printed circuit board type heat exchanger with variable ratio of hot and cold heat exchange plates according to claim 4, characterized in that: The ratio of the hot fluid heat exchange plate (7) to the cold fluid heat exchange plate (8) is (1-10):(1-10).

6. The printed circuit board type heat exchanger with variable ratio of hot and cold heat exchange plates according to claim 4, characterized in that: The hot fluid flow channel (9) and the cold fluid flow channel (10) are arranged in countercurrent, the hot fluid flow channel inlet end (11) and the cold fluid flow channel outlet end (14) are located on the same side of the heat exchanger core, and the hot fluid flow channel outlet end (12) and the cold fluid flow channel inlet end (13) are located on the same side of the heat exchanger core.

7. The printed circuit board type heat exchanger with variable ratio of hot and cold heat exchange plates according to claim 6, characterized in that: The hot fluid inlet pipe (3) and the cold fluid outlet pipe (6) are arranged at intervals, and the hot fluid outlet pipe (4) and the cold fluid inlet pipe (5) are arranged at intervals.

8. The printed circuit board type heat exchanger with variable ratio of hot and cold heat exchange plates according to claim 4, characterized in that: The hot fluid flow channel (9) and the cold fluid flow channel (10) are straight flow channels or broken-line flow channels.

9. The printed circuit board type heat exchanger with variable ratio of hot and cold heat exchange plates according to claim 4, wherein: The cross-sections of the hot fluid flow channel (9) and the cold fluid flow channel (10) are semi-circular.

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