A thermal design method for multi-process diffusion-bonded compact plate heat exchanger

Abstract

The present invention provides a thermal design method for a multi-process diffusion-welded compact plate heat exchanger, comprising: performing pre-processing of heat exchanger sub-region division according to design requirements, and establishing an equivalent plate heat conduction model and a working fluid flow heat transfer model based on fin efficiency for each sub-region, and using the statistical average idea to calculate the equivalent structural parameters of the sub-region and the thermodynamic parameters of the working fluid; using the temperature field and the pressure field as unknown variables to jointly solve the control body equations of all units, and judging and implementing the adaptive encryption operation of the sub-region based on the solved temperature field and pressure field results, and dividing the sub-region from coarse to fine until a convergent design result independent of the sub-region division is obtained. The method described in the present invention is applicable to the thermal design of a <1‑n> process diffusion-welded compact plate heat exchanger.

Description

Technical Field

[0001] The present invention belongs to the technical field of general heat exchanger design in the energy field, and specifically is a highly efficient thermal design method for a <1-n> process type cold and hot side heterogeneous flow channel diffusion welding compact plate heat exchanger based on statistical average ideas and fin efficiency. Background Art

[0002] The diffusion-welded compact plate heat exchanger is a new type of high-efficiency heat exchanger with the advantages of large heat exchange area per unit volume and high heat transfer coefficient. In addition, due to its high temperature and high pressure resistance and high safety, the diffusion-welded compact plate heat exchanger has broad application prospects in the fields of new energy, fourth-generation nuclear energy systems, new power cycles, refrigeration, petrochemicals, etc. Taking the new generation of supercritical carbon dioxide Brayton cycle as an example, the maximum temperature of this cycle can reach above 800K and the pressure can reach up to 20MPa. Therefore, the diffusion-welded compact plate heat exchanger is one of the suitable choices for the regenerator and cooler in this cycle. In addition, the physical properties of supercritical carbon dioxide such as specific heat and density change dramatically in the quasi-critical region. Different heat exchanger flow channel structure designs have a significant impact on the heat transfer and pressure drop characteristics of supercritical carbon dioxide flow. Advanced heat exchanger thermal design methods can effectively improve the comprehensive thermal hydraulic performance of the heat exchanger.

[0003] In order to match the flow rate, heat transfer and pressure drop requirements of the hot and cold sides, diffusion-welded compact plate heat exchangers are usually arranged in multiple processes in industrial applications, such as the common <1-n> process type cold and hot side heterogeneous flow channel diffusion-welded compact plate heat exchanger. Diffusion-welded compact plate heat exchangers have straight flow channels, zigzag flow channels, and wing-shaped flow channels. Due to the large number of flow channels and complex structure of the <1-n> process type cold and hot side heterogeneous flow channel diffusion-welded compact plate heat exchanger, it is difficult to directly use the existing design program simplified to counterflow, crossflow and cocurrent for calculation, and the computational fluid dynamics method requires huge computing resources and has low computing efficiency. The multi-process arrangement of the flow channel means that the flow direction of the flow channel changes many times, and the conventional lumped parameter method is no longer applicable; in addition, the compact plate heat exchanger is composed of tens of thousands of tiny flow channels, and the thermodynamic parameters of the fluid in adjacent similar structure flow channels are relatively small. The conventional single modeling analysis of each flow channel will cause a lot of computing power waste. Based on this, the present invention proposes a rapid design method for a <1-n> process type cold and hot side heterogeneous flow channel diffusion welding compact plate heat exchanger based on the statistical average concept and fin efficiency. Summary of the invention

[0004] The present invention aims at the technical problems existing in the prior art and provides a thermal design method for a multi-process diffusion-welded compact plate heat exchanger. This technical solution can calculate the next step of heat exchange efficiency and flow pressure drop in the most efficient way while ensuring the calculation accuracy, thus greatly saving calculation time.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows: a thermal design method for a multi-flow <1-n> type diffusion-welded compact plate heat exchanger, the thermal design process of the multi-flow <1-n> type diffusion-welded compact plate heat exchanger comprises the following steps:

[0006] Step 1: Perform initial sub-region division on the <1-n> process type cold and hot side heterogeneous flow channel diffusion welding compact plate heat exchanger. First, divide the process turning into initial sub-regions, and each turning sub-region contains 1 diagonal line of the n-process heat exchanger plate process turning outward; then divide the initial sub-region of the non-turning area, and the initial sub-region length-width ratio of the non-turning area is maintained between 0.5-2. In each sub-region, the hot and cold side fluid and solid heat conduction areas together constitute the corresponding control body.

[0007] Step 2: Based on the composite flow channel style and structure contained in the initial sub-region, an equivalent flat plate heat conduction model and an equivalent model of the corresponding one-dimensional flow of hot and cold fluids in the flow channel are established. The heat conduction between the hot and cold fluids in the region through the heat exchanger wall is equivalent to the flat plate heat conduction problem considering the fin efficiency. Based on the statistical average idea, the structural parameters such as the equivalent flat plate heat conduction wall thickness, the equivalent flat plate heat exchange area, and the temperature and pressure equivalent fluid thermodynamic parameters in each sub-region are obtained. The specific steps of step 2 are as follows:

[0008] An equivalent flat plate wall heat conduction model is established. Based on the statistical average idea, the solid heat conduction area of ​​the non-fin area in the divided area is equivalent to the flat plate heat conduction. The calculation formula for the equivalent thickness of the flat plate wall is:

[0009] ,

[0010] in, is the equivalent solid thickness; is the total volume of all solid heat conduction areas except the fin structure in the divided area, It is the vertical projection area of ​​the divided area.

[0011] A one-dimensional flow equivalent length model is established in the sub-region. Based on the statistical average idea, the calculation formula for the one-dimensional flow equivalent length in the sub-region is:

[0012] ,

[0013] in, is the equivalent length of one-dimensional flow in the sub-region; is the total length of the flow channel in the divided area, is the number of parallel flow channels in the divided area.

[0014] Step 3: Based on the equivalent model and equivalent parameters of step 2, establish the following control body conservation equations for the cold side and hot side fluids of each divided unit:

[0015] ,

[0016] In the above three formulas, is the density, is the mass flow rate, is the axial length of the flow channel, For pressure, is the Fanning friction coefficient, is the wetted perimeter of the flow channel, is the acceleration due to gravity, is the specific enthalpy of the working fluid, is the heat flux per unit length, is the heat exchange area, is the cross-sectional area of ​​the flow channel. The above three heat exchanger flow and heat transfer models based on conservation equations are discretized on each control body. The lumped temperature of each control body is used as the temperature node. The boundary temperature between two adjacent control bodies is the average of the lumped temperatures of the two control bodies. The energy conservation equation in the control equation is discretized and applied to all control bodies. For a control entity:

[0017] ,

[0018] The subscript , Represents the parameters of the hot side or cold side, respectively, , Represent the parameters of the control body export or import, respectively, Representative The total heat transfer coefficient Based on the heat exchange area calculation on the hot side, the calculation formula is as follows:

[0019] ,

[0020] In the formula, , are the heat exchange areas on the cold side and the hot side, respectively. and are the convective heat transfer coefficients on the cold side and the hot side, respectively, The equivalent solid thickness is obtained by dividing the solid volume between the cold and hot side channels by the heat exchange area on the hot side. is the hot side equivalent fin efficiency, is the cold side equivalent fin efficiency. The calculation formulas for the hot side equivalent fin efficiency and the cold side equivalent fin efficiency are as follows:

[0021] ,

[0022] in, Defined as , is the working fluid convection heat transfer coefficient, is the solid area thermal conductivity, is the dimensionless thickness, is the hot side fin efficiency, is the cold side fin efficiency; The calculation formula is:

[0023] ,

[0024] In the above formula, is the minimum thickness of the fin area in the semicircular flow channel, is the radius of the semicircular flow channel. The temperature at the root of the fin is used to characterize the wall temperature of the section. and The calculation formula is as follows:

[0025] .

[0026] Step 4: Solve the equations of all units with temperature field as unknown quantity simultaneously to obtain the preliminary results of the temperature field inside the <1-n> process-type hot and cold side heterogeneous flow channel diffusion welding compact plate heat exchanger. Update the physical properties of the fluid based on the temperature field distribution results, and calculate the pressure field distribution of the heat exchanger. The specific steps of step 4 are as follows: the system of equations with temperature field as unknown quantity established in step 3 is solved by using the BICGSTAB method which has good robustness and fast convergence speed in solving large sparse matrices; two conjugate directions are used to approximate the solution vector in each iteration when implementing the BICGSTAB method, specifically, the iteration vector (solution vector) and the residual vector are first initialized; during the iteration process, the two conjugate directions of the residual vector are calculated, and the solution vector is approximated based on the two conjugate directions; the solution vector is then corrected based on the residual, and the above two steps of "approximation-correction" are repeated until the preset convergence condition is reached or the maximum number of iterations is reached; the system of temperature field equations is solved by the above BICGSTAB method to obtain preliminary results of the temperature field inside the <1-n> process-type cold and hot side heterogeneous flow channel diffusion welding compact plate heat exchanger, the physical properties of the fluid are updated according to the temperature field distribution results, and the pressure field distribution of the heat exchanger is calculated.

[0027] Step five, based on step four, encrypt the initial sub-area division of the <1-n> process type cold and hot side heterogeneous flow channel diffusion welding compact plate heat exchanger. The encryption method is to divide the diagonal of the n-process heat exchange plate process turning point into two equal parts, and draw lines along the equal division point in the horizontal and vertical dimensions for encryption. Then perform the calculations of steps two to four on the encrypted sub-area. Determine whether the difference between the temperature field and the pressure field before and after encryption reaches the given convergence criterion. If the convergence criterion is not met, continue to perform adaptive encryption and calculation of the diagonal bisection method in the sub-area at the turning point of the n-process heat exchange plate process; if the convergence criterion is met, store and output the calculation results, and end the design calculation.

[0028] The heat exchanger comprises a multi-flow diffusion-welded compact plate heat exchanger, comprising a multi-flow <1-n> type diffusion-welded compact plate heat exchanger core, a single-flow heat exchange plate inlet header in the multi-flow <1-n> type diffusion-welded compact plate heat exchanger, a single-flow heat exchange plate outlet header in the multi-flow <1-n> type diffusion-welded compact plate heat exchanger, an n-flow heat exchange plate inlet header in the multi-flow <1-n> type diffusion-welded compact plate heat exchanger, an n-flow heat exchange plate outlet header in the multi-flow <1-n> type diffusion-welded compact plate heat exchanger, a single-flow heat exchange plate inlet header pipe in the multi-flow <1-n> type diffusion-welded compact plate heat exchanger, and a single-flow heat exchange plate in the multi-flow <1-n> type diffusion-welded compact plate heat exchanger. The outlet header of the heat exchanger plate, the inlet header of the n-pass heat exchanger plate in the multi-pass <1-n> type diffusion welding compact plate heat exchanger, and the outlet header of the n-pass heat exchanger plate in the multi-pass <1-n> type diffusion welding compact plate heat exchanger; the multi-pass <1-n> type diffusion welding compact plate heat exchanger core includes the upper and lower covers of the multi-pass <1-n> type diffusion welding compact plate heat exchanger core, the n-pass heat exchanger plate in the multi-pass <1-n> type diffusion welding compact plate heat exchanger core, and the single-pass heat exchanger plate in the multi-pass <1-n> type diffusion welding compact plate heat exchanger core, and the cold and hot side heat exchanger plates are alternately stacked; the flow channel on the cold and hot side heat exchanger plate is one of a photochemically etched semicircular straight flow channel and a broken line flow channel. The hot and cold side fluids of the heat exchanger are arranged in countercurrent, that is, the cold and hot side inlets are distributed at both ends of the diffusion welding compact plate heat exchanger.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (1) The present invention relates to a <1-n> process type cold and hot side heterogeneous flow channel diffusion welding compact plate heat exchanger thermal design method, which adopts the form of spatial discretization of the heat exchanger and then calculates the equivalent structural parameters and fluid thermodynamic parameters of each discretized unit using statistical methods and equivalent model methods, and then jointly solves the control volume energy conservation equation and equivalent wall heat conduction equation of all units for calculation, avoiding direct modeling and meshing of the heat exchanger composed of hundreds of thousands of micro channels, which can greatly reduce the difficulty of modeling and the number of meshes. Compared with the conventional computational fluid dynamics calculation method, the calculation amount can be reduced by more than 90%, and the same thermal design accuracy can be achieved.

[0031] (2) The adaptive optimization and adjustment of the regional division method of the present invention can quickly find the optimal regional division method in the thermal design of different diffusion welding compact heat exchangers, and can perform the next step of heat transfer efficiency and flow pressure drop calculation in the most efficient way while ensuring the calculation accuracy, saving 5-15 times of calculation time.

[0032] (3) The present invention divides and models the whole process area of ​​the multi-process diffusion welding compact plate heat exchanger. Compared with the traditional equivalent heat transfer unit number thermal design method, the traditional equivalent heat transfer unit number thermal design error can be reduced from 20% to within 5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of a <1-n> process type diffusion welding compact plate heat exchanger;

[0034] Figure 2 This is a schematic diagram of the heat exchange plate for n processes;

[0035] Figure 3 It is a schematic diagram of a single-process heat exchange plate;

[0036] Figure 4 It is a schematic diagram of a heat exchange plate with a semicircular cross-section and a straight channel;

[0037] Figure 5 It is a schematic diagram of a heat exchange plate with a semicircular cross-section and a broken-line flow channel;

[0038] Figure 6 Thermal design flow chart for multi-process <1-n> type diffusion-welded compact plate heat exchanger;

[0039] Figure 7 Schematic diagram of the initial sub-area division method of the n-process heat exchange plate along the process turning diagonal line;

[0040] Figure 8 Schematic diagram of adaptive encryption method for dividing n-process heat exchanger plates into diagonal sub-areas along the process corners;

[0041] Fig. 9It is a schematic diagram of the semicircular flow channel structure and geometric parameters;

[0042] Fig.10 This is a schematic diagram of a 5-process heat exchange plate;

[0043] Fig.11 Schematic diagram of the initial sub-area division method of the <1-5> process type diffusion welding compact plate heat exchanger;

[0044] Fig.12 A schematic diagram of adaptive encryption of the initial sub-area of ​​the <1-5> process type diffusion-welded compact plate heat exchanger;

[0045] Fig.13 The <1-5> schematic diagram of the process type diffusion welding compact plate heat exchanger;

[0046] Fig.14 The temperature distribution on the cold side of the diffusion-welded compact plate heat exchanger of process type <1-5>;

[0047] Fig.15 The hot side temperature distribution of the diffusion-welded compact plate heat exchanger of process type <1-5>;

[0048] Fig.16 The relative outlet pressure distribution on the cold side of the process type <1-5> diffusion welded compact plate heat exchanger;

[0049] Fig.17 Relative outlet pressure distribution on the hot side of a diffusion-welded compact plate heat exchanger of process type <1-5>.

[0050] In the figure: 101 is a multi-pass <1-n> type diffusion welded compact plate heat exchanger core; 101-1 is a multi-pass <1-n> type diffusion welded compact plate heat exchanger core upper and lower covers; 101-2 is an n-pass heat exchange plate in a multi-pass <1-n> type diffusion welded compact plate heat exchanger core; 101-3 is a single-pass heat exchange plate in a multi-pass <1-n> type diffusion welded compact plate heat exchanger core; 102-1 is an inlet header for a single-pass heat exchange plate in a multi-pass <1-n> type diffusion welded compact plate heat exchanger; 102-2 102-1 is the outlet header of the single-pass heat exchanger plate in the multi-pass <1-n> type diffusion welded compact plate heat exchanger; 102-3 is the inlet header of the n-pass heat exchanger plate in the multi-pass <1-n> type diffusion welded compact plate heat exchanger; 102-4 is the outlet header of the n-pass heat exchanger plate in the multi-pass <1-n> type diffusion welded compact plate heat exchanger; 103-1 is the inlet header of the single-pass heat exchanger plate in the multi-pass <1-n> type diffusion welded compact plate heat exchanger; 103-2 is the single-pass heat exchanger plate in the multi-pass <1-n> type diffusion welded compact plate heat exchanger. 103-3 is the n-pass heat exchange plate inlet header pipe in multi-pass <1-n> type diffusion welding compact plate heat exchanger; 103-4 is the n-pass heat exchange plate outlet header pipe in multi-pass <1-n> type diffusion welding compact plate heat exchanger; 201-1 is the first pass of the n-pass heat exchange plate; 201-2 is the first pass turn of the n-pass heat exchange plate; 202-1 is the second pass of the n-pass heat exchange plate; 202-2 is the second pass turn of the n-pass heat exchange plate; 203-1 is the n-pass heat exchange plate 203-2 is the third process of the n process heat exchange plate; 204-1 is the n-1th process of the n process heat exchange plate; 204-2 is the n-1th process turn of the n process heat exchange plate; 205 is the nth process of the n process heat exchange plate; 701 is the diagonal line of the process turn of the n process heat exchange plate; 702 is the initial sub-area determined based on the process turn diagonal line (in the dotted box); 703 is the initial sub-area of ​​the non-turning area (in the dotted box); 801 is the n-1th process based on which the binary method encryption is implemented Diagonal line at the process turning point of the process heat exchange plate; 802 is the sub-area (in the dotted box) after adaptive encryption once determined based on the process turning diagonal line and the dichotomy method; 803 is the sub-area (in the dotted box) after the non-turning area is encrypted accordingly according to the adaptive encryption method of the turning area; 901 is the hot side heat exchange plate; 902 is the cold side heat exchange plate; 903 is the fin area; 904 is the non-fin solid area; 1001-1 is the first process of the five-process heat exchange plate; 1001-2 is the first process turning point of the five-process heat exchange plate; 1002-1 is the second process of the five-process heat exchange plate; 1002-2 is the second process turning point of the five-process heat exchange plate; 1003-1 is the third process of the five-process heat exchange plate; 1003-2 is the third process turning point of the five-process heat exchange plate; 1004-1 is the fourth process of the five-process heat exchange plate; 1004-2 is the fourth process turning point of the five-process heat exchange plate;1005 is the fifth process of the five-process heat exchange plate; 1301 is a multi-process <1-5> type diffusion welded compact plate heat exchanger including a heat exchange core; 1301-1 is a multi-process <1-5> type diffusion welded compact plate heat exchanger core upper and lower covers; 1301-2 is a five-process heat exchange plate in the multi-process <1-5> type diffusion welded compact plate heat exchanger core; 1301-3 is a single-process heat exchange plate in the multi-process <1-5> type diffusion welded compact plate heat exchanger core; 1302-1 is an inlet header for a single-process heat exchange plate in a multi-process <1-5> type diffusion welded compact plate heat exchanger; 1302-2 is an outlet header for a single-process heat exchange plate in a multi-process <1-5> type diffusion welded compact plate heat exchanger; 130 2-3 is the inlet header of the five-pass heat exchanger plate in the multi-pass <1-5> type diffusion welding compact plate heat exchanger; 1302-4 is the outlet header of the five-pass heat exchanger plate in the multi-pass <1-5> type diffusion welding compact plate heat exchanger; 1303-1 is the inlet header pipe of the single-pass heat exchanger plate in the multi-pass <1-5> type diffusion welding compact plate heat exchanger; 1303-2 is the outlet header pipe of the single-pass heat exchanger plate in the multi-pass <1-5> type diffusion welding compact plate heat exchanger; 1303-3 is the inlet header pipe of the five-pass heat exchanger plate in the multi-pass <1-5> type diffusion welding compact plate heat exchanger; 1303-4 is the outlet header pipe of the five-pass heat exchanger plate in the multi-pass <1-5> type diffusion welding compact plate heat exchanger. ; DETAILED DESCRIPTION

[0051] In order to deepen the understanding of the present invention, the thermal design embodiment of the process-type diffusion welding compact plate heat exchanger <1-5> is described in detail with reference to the accompanying drawings. In this embodiment, both the cold and hot side heat exchange plates are semicircular cross-section straight channel heat exchange plates.

[0052] Example 1: <1-5> Thermal design method for process-type diffusion-welded compact plate heat exchanger,

[0053] Diffusion welded compact plate heat exchanger single pass heat exchanger plate Figure 3 As shown, the 5-process heat exchange plate is as follows Fig.10 This embodiment includes the following steps:

[0054] S101, confirm whether the design objectives and design conditions of the diffusion-welded compact plate heat exchanger in process <1-5> are complete, and perform initial sub-region division on the flow channel area of ​​the heat exchanger. An initial sub-region division method is as follows: Fig.11 shown.

[0055] S102, based on the composite flow channel style and structure contained in each divided unit, establish an equivalent flat plate heat conduction model and an equivalent model of the corresponding one-dimensional flow of hot and cold fluids in the flow channel. The heat conduction between the hot and cold fluids in the region through the wall of the heat exchanger is equivalent to the flat plate heat conduction problem considering the fin efficiency. Based on the statistical average idea, the equivalent flat plate heat conduction wall thickness, equivalent flat plate heat exchange area and other structural parameters and the temperature and pressure equivalent fluid thermodynamic parameters in each sub-region are obtained. The specific method for establishing an equivalent flat plate wall heat conduction model is as follows: Based on the statistical average idea, the solid heat conduction area of ​​the non-fin area in the divided sub-region is equivalent to flat plate heat conduction, and the equivalent thickness calculation formula of the flat plate wall is:

[0056]

[0057] in, is the equivalent solid thickness; is the total volume of all solid heat conduction areas except the fin structure in the divided area, It is the vertical projection area of ​​the divided area.

[0058] A one-dimensional flow equivalent length model is established in the sub-region. Based on the statistical average idea, the calculation formula for the one-dimensional flow equivalent length in the sub-region is:

[0059] ,

[0060] in, is the equivalent length of one-dimensional flow in the sub-region; is the total length of the flow channel in the divided area, is the number of parallel flow channels in the divided area.

[0061] S103, based on the equivalent model and equivalent parameters of step 2, establish the following control body conservation equations for the cold side and hot side fluids of each divided unit:

[0062] ,

[0063] In the above three formulas, is the density, is the mass flow rate, is the axial length of the flow channel, For pressure, is the Fanning friction coefficient, is the wetted perimeter of the flow channel, is the acceleration due to gravity, is the specific enthalpy of the working fluid, is the heat flux per unit length, is the heat exchange area, is the cross-sectional area of ​​the flow channel. The above three heat exchanger flow and heat transfer models based on conservation equations are discretized on each control body. The lumped temperature of each control body is used as the temperature node. The boundary temperature between two adjacent control bodies is the average of the lumped temperatures of the two control bodies. The energy conservation equation in the control equation is discretized and applied to all control bodies. For a control entity:

[0064] ,

[0065] The subscript , Represents the parameters of the hot side or cold side, respectively, , Represent the parameters of the control body export or import, respectively, Representative The total heat transfer coefficient Based on the heat exchange area calculation on the hot side, the calculation formula is as follows:

[0066] ,

[0067] In the formula, , are the heat exchange areas on the cold side and the hot side, respectively. and are the convective heat transfer coefficients on the cold side and the hot side, respectively, The equivalent solid thickness is obtained by dividing the solid volume between the cold and hot side channels by the heat exchange area on the hot side. is the hot side equivalent fin efficiency, is the cold side equivalent fin efficiency. The calculation formulas for the hot side equivalent fin efficiency and the cold side equivalent fin efficiency are as follows:

[0068] ,

[0069] in, Defined as , is the working fluid convection heat transfer coefficient, is the solid area thermal conductivity, is the dimensionless thickness, is the hot side fin efficiency, is the cold side fin efficiency; The calculation formula is:

[0070] ,

[0071] In the above formula, is the minimum thickness of the fin area in the semicircular flow channel, is the radius of the semicircular flow channel. The temperature at the root of the fin is used to characterize the wall temperature of the section. and The calculation formula is as follows:

[0072] .

[0073] S104, solving the equation group with temperature field as unknown quantity established in step 3 by using BICGSTAB method which has good robustness and fast convergence speed in solving large sparse matrices. When implementing BICGSTAB method, two conjugate directions are used to approximate the solution vector in each iteration. Specifically, the iteration vector (solution vector) and the residual vector are initialized first. During the iteration, the two conjugate directions of the residual vector are calculated, and the solution vector is approximated based on the two conjugate directions. Then, the solution vector is corrected based on the residual, and the above two steps of "approximation-correction" are repeated until the preset convergence condition is reached or the maximum number of iterations is reached; the temperature field equation group is solved by the above BICGSTAB method to obtain the preliminary results of the temperature field inside the <1-5> process type cold and hot side heterogeneous flow channel diffusion welding compact plate heat exchanger, update the physical properties of the fluid according to the temperature field distribution results, and calculate the pressure field distribution of the heat exchanger.

[0074] S105, based on step 4, encrypt the initial sub-region division of the process type <1-5> hot and cold side heterogeneous flow channel diffusion welding compact plate heat exchanger. Fig.12 As shown, the encryption method is to divide the diagonal of the five-pass heat exchange plate flow turning point into two equal parts, and draw lines along the equal division points in the horizontal and vertical dimensions for encryption. Then perform the calculations of steps 2 to 4 on the encrypted sub-area. Determine whether the difference between the temperature field and the pressure field before and after encryption reaches the given convergence criterion. If the convergence criterion is not reached, continue to perform adaptive encryption and calculation of the diagonal bisection method in the sub-area at the turning point of the n-pass heat exchange plate flow; if the convergence criterion is reached, store and output the calculation results, and end the design calculation.

[0075] Example 2: <1-5> Process diffusion welding compact plate heat exchanger, such as Fig.13 As shown,

[0076] The <1-5> type diffusion welded compact plate heat exchanger comprises a heat exchange core 1301, a single-flow heat exchange plate inlet header 1302-1 in a multi-flow <1-5> type diffusion welded compact plate heat exchanger, a single-flow heat exchange plate outlet header 1302-2 in a multi-flow <1-5> type diffusion welded compact plate heat exchanger, a five-flow heat exchange plate inlet header 1302-3 in a multi-flow <1-5> type diffusion welded compact plate heat exchanger, a five-flow heat exchange plate outlet header 1302-4 in a multi-flow <1-5> type diffusion welded compact plate heat exchanger, a single-flow heat exchange plate in a multi-flow <1-5> type diffusion welded compact plate heat exchanger, and a heat exchange plate ... The inlet header pipe of the heat exchange plate in the multi-pass <1-5> type diffusion welding compact plate heat exchanger is 1303-1, the outlet header pipe of the heat exchange plate in the single-pass flow in the multi-pass <1-5> type diffusion welding compact plate heat exchanger is 1303-2, the inlet header pipe of the heat exchange plate in the five-pass flow in the multi-pass <1-5> type diffusion welding compact plate heat exchanger is 1303-3, and the outlet header pipe of the heat exchange plate in the five-pass flow in the multi-pass <1-5> type diffusion welding compact plate heat exchanger is 1303-4; the multi-pass <1-5> type diffusion welding compact plate heat exchanger core 1301 includes the upper and lower covers of the multi-pass <1-5> type diffusion welding compact plate heat exchanger core 1301-1, the multi-pass <1 -5> type diffusion welded compact plate heat exchanger core body five-pass heat exchange plate 1301-2, multi-pass <1-5> type diffusion welded compact plate heat exchanger core body single-pass heat exchange plate 1301-3; multi-pass <1-5> type diffusion welded compact plate heat exchanger core body five-pass heat exchange plate 1301-2 and single-pass heat exchange plate 1301-3 are alternately stacked; single-pass heat exchange plate inlet header 1302-1 and single-pass heat exchange plate outlet header 1302-2 are welded at both ends of heat exchange core body 1301; five-pass heat exchange plate inlet header 1302-3 and five-pass heat exchange plate outlet header 1302 -4 is welded on the sides of both ends of the heat exchange core 1301; the single-flow heat exchange plate inlet header pipe 1303-1 is welded on the single-flow heat exchange plate inlet header 1302-1; the single-flow heat exchange plate outlet header pipe 1303-2 is welded on the single-flow heat exchange plate outlet header 1302-2; the five-flow heat exchange plate inlet header pipe 1303-3 is welded on the five-flow heat exchange plate inlet header 1302-3; the five-flow heat exchange plate outlet header pipe 1303-4 is welded on the five-flow heat exchange plate outlet header 1302-4; the flow channel on the hot and cold side heat exchange plates is a photochemically etched semicircular straight flow channel, such as Figure 4 As shown, the fluids on the hot and cold sides of the heat exchanger flow in countercurrent.

[0077] Given the cold side inlet 273.15K, 0.2MPa, air flow rate 5kg / (m 2 ·s), hot side inlet 573.15K, 0.2MPa, air flow rate 3kg / (m 2 ·s) working condition, the design method of this application is used to design the cold side temperature distribution of the <1-5> process type heat exchanger as follows Fig.14 As shown, the temperature distribution on the hot side is Fig.15 As shown, the cold side pressure drop distribution is as follows Fig.16 As shown, the hot side pressure drop distribution is as follows Fig.17 The thermal design method invented in this application only requires 4 encryption steps, takes 5 seconds to calculate, and uses 25MB of memory. Compared with the above-mentioned traditional method, the calculation time is shortened to 1 / 12, the calculation resources are reduced to 1 / 40, and the calculation deviation is increased from 0.5% to 0.1%.

[0078] It should be noted that the above embodiments are not intended to limit the protection scope of the present invention, and equivalent changes or substitutions made on the basis of the above technical solutions all fall within the protection scope of the claims of the present invention.

Claims

1. A thermal design method for a multi-process diffusion-bonded compact plate heat exchanger, characterized in that: The method comprises the following steps: Step 1: Initial sub-region division of the <1-n> process type cold and hot side heterogeneous flow channel diffusion welding compact plate heat exchanger. Step 2: Based on the composite flow channel patterns and structures contained in each divided sub-region, the equivalent plate heat conduction distance model and the corresponding one-dimensional flow equivalent length model of the hot and cold fluids in the sub-region are established by using the statistical average method. Step 3: Based on the equivalent model and equivalent parameters of step 2, establish the energy conservation equations of the control bodies of the cold side and hot side fluids of each divided unit and the equivalent wall heat conduction equations, and establish a set of equations between each control body with the total temperature of the control body as the variable. Determine the boundary conditions according to the given thermodynamic state of the cold and hot side inlets, and finally determine the set of equations with the temperature field as the unknown quantity. Step 4: Solve the above equations with temperature field as unknown quantity by BICGSTAB solution algorithm, and obtain the temperature field distribution inside the <1-n> process type cold and hot side heterogeneous flow channel diffusion welding compact plate heat exchanger. Update the physical properties of the fluid according to the temperature field distribution results, and calculate the pressure field distribution of the heat exchanger. Step 5. Based on step 4, the initial sub-region division of the <1-n> process type diffusion welding compact plate heat exchanger is encrypted by bisecting the diagonal at the turning point of the n-process heat exchanger plate, and steps 2 to 4 are repeated until the calculation deviation of the temperature field, physical field, and pressure field twice is less than 0.1%. Stop the sub-region division encryption and calculation, and output the last temperature field and pressure field calculation results as thermal design results.

2. The thermal design method of a multi-process diffusion-bonded compact plate heat exchanger according to claim 1, characterized in that: Step 1: Perform initial sub-region division on the <1-n> process type cold and hot side heterogeneous flow channel diffusion welding compact plate heat exchanger. First, divide the process turning point into initial sub-regions. Each turning sub-region contains 1 diagonal line of the n-process heat exchange plate process turning point. Then, perform initial sub-region division on the non-turning area. The aspect ratio of the initial sub-region of the non-turning area is maintained between 0.5 and 2. In each sub-region, the hot and cold side fluid and solid heat conduction areas together constitute the corresponding control body.

3. The thermal design method of a multi-process diffusion-bonded compact plate heat exchanger according to claim 1, characterized in that: The step 2 is specifically as follows: An equivalent flat plate wall heat conduction model is established. Based on the statistical average idea, the solid heat conduction area of ​​the non-fin area in the divided area is equivalent to the flat plate heat conduction. The calculation formula for the equivalent thickness of the flat plate wall is: in, is the equivalent solid thickness; is the total volume of all solid heat conduction areas except the fin structure in the divided area, is the vertical projection area of ​​the divided area, A one-dimensional flow equivalent length model is established in the sub-region. Based on the statistical average idea, the calculation formula for the one-dimensional flow equivalent length in the sub-region is: ， in, is the equivalent length of one-dimensional flow in the sub-region; is the total length of the flow channel in the divided area, is the number of parallel flow channels in the divided area.

4. The thermal design method of a multi-process diffusion-bonded compact plate heat exchanger according to claim 1, characterized in that: Step 3 is as follows: According to the equivalent model and equivalent parameters in step 2, the control body conservation equations of the cold side and hot side fluids of each divided unit are established as follows: ， In the above three formulas, is the density, is the mass flow rate, is the axial length of the flow channel, For pressure, is the Fanning friction coefficient, is the wetted perimeter of the flow channel, is the acceleration due to gravity, is the specific enthalpy of the working fluid, is the heat flux per unit length, is the heat exchange area, is the cross-sectional area of ​​the flow channel. The above three heat exchanger flow and heat transfer models based on conservation equations are discretized on each control body. The lumped temperature of each control body is used as the temperature node. The boundary temperature between two adjacent control bodies is the average of the lumped temperatures of the two control bodies. The energy conservation equation in the control equation is discretized and applied to all control bodies. For a control entity: ， The subscript , Represents the parameters of the hot side or cold side, respectively, , Represent the parameters of the control body export or import, respectively, Representative The total heat transfer coefficient Based on the heat exchange area calculation on the hot side, the calculation formula is as follows: ， In the formula, , are the heat exchange areas on the cold side and the hot side, respectively. and are the convective heat transfer coefficients on the cold side and the hot side, respectively, The equivalent solid thickness is obtained by dividing the solid volume between the cold and hot side channels by the heat exchange area on the hot side. is the hot side equivalent fin efficiency, is the cold side equivalent fin efficiency, the hot side equivalent fin efficiency and the cold side equivalent fin efficiency are calculated as follows: ， in, Defined as , is the working fluid convection heat transfer coefficient, is the solid area thermal conductivity, is the dimensionless thickness, is the hot side fin efficiency, is the cold side fin efficiency; The calculation formula is: ， In the above formula, is the minimum thickness of the fin area in the semicircular flow channel, is the radius of the semicircular flow channel, and the temperature at the root of the fin is taken to represent the wall temperature of the section. and The calculation formula is as follows: 。 5. The thermal design method of a multi-process diffusion-bonded compact plate heat exchanger according to claim 1, characterized in that: Step 4 is as follows: The BICGSTAB method is used to solve the equations with the temperature field as the unknown quantity established in step 3. When implementing the BICGSTAB method, two conjugate directions are used to approximate the solution vector in each iteration. Specifically, the iteration vector and the residual vector are initialized first. During the iteration process, the two conjugate directions of the residual vector are calculated, and the solution vector is approximated based on the two conjugate directions. The solution vector is then corrected based on the residual, and the above "approximation-correction" steps are repeated until the preset convergence condition is reached or the maximum number of iterations is reached; the temperature field equations are solved by the above BICGSTAB method to obtain the preliminary results of the temperature field inside the <1-n> process-type diffusion welding compact plate heat exchanger, and the physical properties of the fluid are updated according to the temperature field distribution results, and the pressure field distribution of the heat exchanger is calculated. When calculating the pressure field distribution, the pressure drop calculation formula in each sub-region is as follows: in, is the total pressure drop of the hot or cold fluid in the sub-area, is the Fanning coefficient, is the total local resistance coefficient, is the one-dimensional equivalent flow length, is the equivalent hydraulic diameter, is the mass flow rate, is the density, subscript Indicates the exit, subscript Indicates the entrance. It is the pressure drop at the heavy position.

6. The thermal design method of a multi-process diffusion-bonded compact plate heat exchanger according to claim 1, characterized in that: Step 5: The specific process is as follows: The method for encrypting the initial sub-area division is to divide the diagonal line of the turning point of the n-process heat exchanger plate into two equal parts, draw lines along the dividing point in the horizontal and vertical dimensions for encryption, and then perform step 2-step 4 calculations on the encrypted sub-area to determine whether the difference between the temperature field and the pressure field before and after encryption reaches the given convergence criterion. If the convergence criterion is not reached, continue to perform adaptive encryption and calculation of the diagonal line in the sub-area of ​​the turning point of the n-process heat exchanger plate; if the convergence criterion is reached, store and output the calculation results, and end the design calculation.

7. A compact plate heat exchanger with diffusion welding of flow channels, characterized in that: The design method according to any one of claims 1 to 6 is used for design, wherein the heat exchanger comprises a heat exchange core, an inlet header for a single-flow heat exchange plate in a multi-flow <1-n> type diffusion welded compact plate heat exchanger, an outlet header for a single-flow heat exchange plate in a multi-flow <1-n> type diffusion welded compact plate heat exchanger, an inlet header for n-flow heat exchange plates in a multi-flow <1-n> type diffusion welded compact plate heat exchanger, an outlet header for n-flow heat exchange plates in a multi-flow <1-n> type diffusion welded compact plate heat exchanger, an inlet header pipe for a single-flow heat exchange plate in a multi-flow <1-n> type diffusion welded compact plate heat exchanger, an outlet header pipe for a single-flow heat exchange plate in a multi-flow <1-n> type diffusion welded compact plate heat exchanger, an inlet header pipe for an n-flow heat exchange plate in a multi-flow <1-n> type diffusion welded compact plate heat exchanger, and a multi-flow <1-n> type diffusion welded compact plate heat exchanger. > type diffusion welded compact plate heat exchanger in n-pass heat exchanger plate outlet header pipe; multi-pass <1-n> type diffusion welded compact plate heat exchanger core includes multi-pass <1-n> type diffusion welded compact plate heat exchanger core upper and lower covers, n-pass heat exchanger plates in multi-pass <1-n> type diffusion welded compact plate heat exchanger core, and single-pass heat exchanger plates in multi-pass <1-n> type diffusion welded compact plate heat exchanger core; n-pass heat exchanger plates and single-pass heat exchanger plates in multi-pass <1-n> type diffusion welded compact plate heat exchanger core are alternately stacked; single-pass heat exchanger plate inlet header and single-pass heat exchanger plate outlet header are welded at both ends of the heat exchanger core; n-pass heat exchanger plate inlet header and n-pass heat exchanger plate outlet header are welded on the sides at both ends of the heat exchanger core; single-pass heat exchanger plate inlet header pipe is welded on single-pass heat exchanger plate inlet header; The outlet header pipe of the single-pass heat exchange plate is welded on the outlet header of the single-pass heat exchange plate; The n-process heat exchange plate inlet header pipe is welded on the n-process heat exchange plate inlet header; the n-process heat exchange plate outlet header pipe is welded on the n-process heat exchange plate outlet header; the flow channel on the cold and hot side heat exchange plates is one of the photochemically etched semicircular straight flow channel and the broken line flow channel.

8. The flow channel diffusion welded compact plate heat exchanger according to claim 7, characterized in that: The hot and cold side fluids are arranged in countercurrent, that is, the hot and cold side inlets are distributed at both ends of the diffusion welded compact plate heat exchanger.

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