A method and system for predicting heat transfer performance of vapor chamber based on thermal resistance network model

Abstract

The present invention discloses a method and system for predicting the heat transfer performance of a vapor chamber based on a thermal resistance network model, including: constructing a thermal resistance network model of a vapor chamber, taking into account the heat diffusion of heat on the evaporation end wall, the heat conduction process of the support column and the powder ring, and the change of the working fluid level inside the wick under different heating powers; the method and system for predicting the heat transfer performance of a vapor chamber proposed on this basis, taking the effective heat diffusion area of ​​the evaporation end wall and the working fluid temperature results as the convergence standard, iteratively updating the thermal resistance network of the vapor chamber, and finally predicting the heat transfer performance of the vapor chamber. The present invention solves the problem that the traditional prediction method has a high degree of simplification of the working process of the vapor chamber or a great demand for computing power, and cannot have good prediction accuracy for each heating power, and realizes the rapid and accurate prediction of the heat transfer performance of the vapor chamber, replaces the multiple repeated experimental processes in the traditional design of the vapor chamber, shortens the design cycle, reduces R&D costs, and promotes the automation of vapor chamber design.

Description

Technical Field

[0001] The present invention relates to the technical field of vapor chambers, and in particular to a method and system for predicting heat transfer performance of vapor chambers based on a thermal resistance network model. Background Art

[0002] Vapor chambers are widely used in smart phones, computer graphics cards, IGBTs and other microelectronic devices due to their flat surface, high thermal conductivity, and strong temperature-averaging performance. However, vapor chambers have a complex structure, and their heat transfer performance is greatly affected by structural parameters. Moreover, for vapor chambers with the same structure, their heat transfer performance will vary greatly in different application scenarios.

[0003] At present, the method for predicting the heat transfer performance of the vapor chamber is mainly numerical analysis, which can be divided into two categories: analytical model and numerical model. However, the internal heat and mass transfer process of the vapor chamber is complex. The analytical model simplifies the working process of the vapor chamber to a high degree and has low prediction accuracy. The numerical model simplifies the working process of the vapor chamber to a low degree and has higher prediction accuracy, but it is difficult to operate and the calculation and solution time generally takes several weeks. At the same time, no matter which model is used, it is impossible to have good prediction accuracy at all heating powers of the vapor chamber, and it is difficult to meet the needs of actual engineering applications. Therefore, the actual design process of the vapor chamber depends entirely on the designer's experience and knowledge. The designer will design experiments according to the use requirements of the vapor chamber and optimize the structural parameters through repeated experimental verification. In this process, it is also necessary to simultaneously design and manufacture the corresponding graphite mold and test mold according to the different structural designs of the vapor chamber each time, which significantly increases the design cost and prolongs the design cycle. Summary of the invention

[0004] Based on the poor practicality of existing methods for predicting the performance of heat spreaders, and the high design cost and long cycle of traditional heat spreaders, the purpose of this application is to provide a method and system for predicting the heat transfer performance of heat spreaders based on a thermal resistance network model. By improving the traditional thermal resistance network model of the heat spreader, a three-dimensional thermal resistance network is established, and the influence of the heat spreader support column, powder ring and liquid injection rate is coupled to make the model closer to the actual working condition of the heat spreader; and a liquid level retreat sub-model is proposed to predict the heat transfer performance of the heat spreader under different heating powers. In this way, the degree of simplification of the working process of the heat spreader is reduced when the model is established, and the calculation cost is reduced while ensuring the prediction accuracy, so as to achieve accurate prediction of the heat transfer performance of the heat spreader under various heating powers, achieve rapid verification of the heat spreader design scheme, reduce the design cost of the heat spreader, improve the design efficiency, and promote the automated design of the heat spreader. At the same time, the entire prediction process only takes a few seconds, which greatly reduces the design cost and shortens the design cycle.

[0005] In order to achieve the above-mentioned purpose, the first technical solution of the present application discloses a method for predicting the heat transfer performance of a vapor chamber based on a thermal resistance network model, such as Figure 4 As shown, the following steps are included:

[0006] S1. Determine the boundary conditions, including the heat source size, heat source power, radiator equivalent heat transfer coefficient and ambient temperature; set the initial value A of the effective heat diffusion area of ​​the evaporation end wall of the heat spreader e0 A is the heat source area s , that is, A e0 =A s , set the initial value of saturated steam temperature T v0 is the radiator fluid inlet temperature T in , that is, T v0 =T in ;

[0007] S2. Construct a heat spreader thermal resistance network model and calculate the thermal resistance of each component;

[0008] S3. Calculate the heat spreader thermal resistance network model constructed in step S2 according to the heat spreader boundary conditions to obtain the effective heat diffusion area A of the evaporation section wall e and saturated steam temperature T v ;

[0009] S4. According to the calculated value of the effective heat diffusion area of ​​the evaporation end wall and the saturated steam temperature, the heat spreader thermal resistance network model is iterated: the effective heat diffusion area A of the evaporation end wall is determined. e and saturated steam temperature T v Whether the result converges, if not, then A e Assign the value of to A e0 , T v Assign the value of v0 , and return to step S2 to update the vapor chamber thermal resistance network model and calculate the thermal resistance of each component again. If the result converges, calculate the temperature difference and the transferred power at both ends of the thermal resistance of each component;

[0010] S5. According to the iteration result of the vapor chamber network model outputted from S4, the resistance value, temperature difference and transfer power of each component of the vapor chamber thermal resistance network model are obtained, and the heat transfer performance of the vapor chamber is calculated;

[0011] The heat spreader thermal resistance network model is based on the following assumptions: the evaporation / condensation phase change process of the working fluid only occurs at the interface between the liquid working fluid and the steam in the wick, and the height of the interface changes with the change of heating power. Different from the prior art model, which generally assumes that the phase change process occurs at the interface between the steam and the wick, and the interface is fixed and does not change, the model assumption of this application is more realistic.

[0012] Furthermore, the construction of the vapor chamber thermal resistance network model specifically includes: analyzing the vapor chamber heat transfer process and selecting the heat transfer structure to determine the thermal resistance formed during the heat transfer process, including:

[0013] Evaporation end wall heat conduction resistance R p,e :Heat is generated through the evaporation end wall by heat conduction;

[0014] Thermal resistance R s : It is formed on the evaporation end wall because the heat source area is smaller than the heat plate area;

[0015] Evaporation end diffusion heat conduction thermal resistance R p,s : After the heat diffuses along the plane of the evaporation end wall, it is formed through the evaporation end wall by heat conduction;

[0016] Support column thermal resistance R sc And powder ring thermal resistance R r :The heat is generated by heat conduction through the support column and the powder ring;

[0017] Thermal resistance R of the wick heat conduction at the evaporation end w,e :Heat is generated by heat conduction through the evaporation end wick;

[0018] Evaporation end phase change thermal resistance R eva : The liquid working medium at the evaporation end absorbs heat and changes phase to vaporize into steam;

[0019] Vapor diffusion thermal resistance R v :The steam quickly diffuses to form the entire steam chamber;

[0020] Condensation phase change thermal resistance: The vapor diffuses to the condensation end liquid absorption core to undergo phase change and condense into liquid, including the phase change thermal resistance R of the condensation end heat source area. con and the phase change thermal resistance R of the non-heat source area at the condensation end con,n ;

[0021] Thermal conduction resistance of the condensation end wick: Heat is formed by heat conduction through the condensation end wick, including the thermal conduction resistance R of the condensation end heat source area wick w,c and the heat conduction resistance R of the liquid absorption core in the non-heat source area at the condensation end w,c,n ;

[0022] Condensation end wall heat conduction thermal resistance: Heat gathers on the condensation end wall, and then passes through the condensation end wall to the radiator by heat conduction, including the condensation end heat source area wall heat conduction thermal resistance R p,c and the heat conduction resistance R of the wall surface in the non-heat source area at the condensation end p,c,n ;

[0023] Convective heat transfer thermal resistance: The heat sink transfers heat to the outside world through convection heat transfer, including the interface thermal resistance between the heat sink and the heat sink and the heat sink thermal resistance, including the convection heat transfer thermal resistance R of the heat source area lcp , non-heat source area convection heat transfer thermal resistance R lcp,n .

[0024] Furthermore, when the heat spreader does not include one or more of the support column, the powder ring, and the condensation end wick, the corresponding support column thermal resistance, powder ring thermal resistance, and condensation end wick thermal conduction thermal resistance are not calculated.

[0025] Furthermore, the diffusion thermal resistance formed by the evaporation end wall surface is calculated using Cardoso's diffusion thermal resistance model. The prior art generally uses Lee's series thermal resistance model for the diffusion thermal resistance model, which cannot thermally calculate the thermal diffusion area. Cardoso's diffusion thermal resistance model is a parallel thermal diffusion thermal resistance model, which can estimate the thermal diffusion area. This model is the basis for the application to use the heat source area as the evaporation area, liquid level change and other factors, and is also the calculation formula for judging whether the model is convergent.

[0026] Furthermore, the heat source area and the non-heat source area are determined according to the size of the heat source, and the support column and the powder ring in the heat source area participate in the heat transfer process of the heat plate, and heat conduction occurs; the heat conduction area and the evaporation phase change area of ​​the wick at the evaporation end are: the heat source area minus the cross-sectional area of ​​the support column and the powder ring in the heat source area. This technical solution divides the heat source area and the non-heat source area, so that the heat conduction and phase change areas of the support column, the powder ring and the wick at the evaporation end can be determined, which is different from the prior art that generally does not consider the heat transfer process of the support column and the powder ring, making the results of this model more accurate.

[0027] Furthermore, the calculation formula of the thermal conduction resistance is:

[0028] Where R is the heat conduction resistance of the heat through the structure, h is the thickness of the heat through the structure along the heat transfer direction, k is the thermal conductivity of the heat through the structure, and A is the heat conduction area of ​​the heat through the structure on the cross section perpendicular to the heat transfer direction;

[0029] Among them, the thermal conduction resistance includes: the thermal conduction resistance of the evaporation end wall (R p,e , R p,s ), thermal conduction resistance R of the evaporation end liquid absorption core w,e , the heat conduction resistance of the condensation end liquid absorption core (R w,c , R w,c,n ), condensation end wall heat conduction thermal resistance (R p,c , R p,c,n ).

[0030] Further, in the heat conduction resistance of the evaporation end wick and the heat conduction resistance of the condensation end wick, the thickness h along the heat transfer direction is the thickness of the liquid working medium inside the wick, which is obtained according to a liquid surface retreat model based on a semi-experimental method, specifically: according to the liquid filling rate of the heat plate and the capillary force difference between the evaporation end wick and the condensation end wick, the initial height h0 of the liquid working medium inside the wick is determined, the wick with large capillary force and the powder ring are filled with liquid working medium, and the wick with small capillary force is not filled with liquid working medium;

[0031] Calculate the change in the liquid level of the liquid working medium inside the wick:

[0032] Wherein, Δh is the liquid level change, Q is the heat source power, ρ l is the density of the working fluid, ε is the porosity of the wick, A l is the area of ​​the liquid level change region, the evaporation end is the area corresponding to the heat source, the condensation end is the entire condensation end liquid absorption core area, and Δt is the buffer time, which is obtained through experiments;

[0033] The thickness of the liquid working medium inside the wick at the evaporation end is: h=h0-Δh;

[0034] The thickness of the liquid working medium inside the liquid wick at the condensation end is: h=h0+Δh.

[0035] Furthermore, when calculating the steam diffusion thermal resistance, the influence of the support column and the powder ring on the steam flow is ignored, and the steam chamber area and the heat source area are converted into circular areas of equal area. The steam diffusion thermal resistance calculation formula is:

[0036]

[0037] Among them, Q eva is the power transferred by phase change, ΔP v is the pressure drop caused by steam flow, which is obtained by integrating the circular area. The calculation formula is:

[0038] Although the prior art has mature formulas for calculating the vapor diffusion thermal resistance, it is unable to calculate the pressure drop of the vapor diffusing to the surroundings, which makes it difficult to calculate the vapor diffusion thermal resistance of the heat spreader; the present application realizes the estimation of the vapor pressure drop by converting the calculation area into an equal-area area, thereby realizing the estimation of the vapor diffusion thermal resistance, thereby improving the calculation accuracy of the model.

[0039] Furthermore, using the inequality Determine the effective heat diffusion area A of the evaporation end wall e Whether the result converges, if not, then A e Assign the value of to A e0, and return to step S2 to update the heat spreader thermal resistance network model and recalculate the thermal resistance of each component: using |T v0 -T v |<0.05 to judge the saturated steam temperature T v Whether the result converges, if not, T v Assign the value of v0 , and return to step S2 to update the vapor chamber thermal resistance network model and calculate the thermal resistance of each component again. If the result converges, calculate the temperature difference and the transferred power at both ends of the thermal resistance of each component;

[0040] The maximum number of loop iterations is set to 50.

[0041] Furthermore, the heat transfer performance of the vapor chamber includes: the overall thermal resistance of the vapor chamber, the center temperature of the evaporation end wall, the temperature difference between the center and the surrounding of the evaporation end wall, and the temperature difference between the center and the surrounding of the condensation surface wall.

[0042] The second technical solution of the present application discloses a heat transfer performance prediction system of a vapor chamber based on a thermal resistance network model, comprising:

[0043] S1. Parameter acquisition module, used to obtain heat spreader structure parameters and boundary condition parameters from the outside and perform data preprocessing;

[0044] S2. The thermal resistance network module obtains the required parameters from the parameter acquisition module, constructs the vapor chamber thermal resistance network model, and updates the vapor chamber thermal resistance network model according to the values ​​of the effective heat diffusion area of ​​the evaporation end wall and the saturated steam temperature returned by the prediction module;

[0045] S3. A prediction module, which calculates the temperature difference at both ends of each component thermal resistance, the transferred power and the heat transfer performance of the vapor chamber, and generates a bar graph based on the results;

[0046] S4. Data storage module, saves the result bar graph in .png format, writes the data related to the structure parameters, boundary condition parameters and heat transfer performance prediction results of the heat spreader into an Excel document, and saves it to a specified path;

[0047] S5. Result display module, outputs and displays the heat transfer performance prediction results of the heat spreader.

[0048] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0049] The present invention comprehensively considers the influence of support columns, powder rings, liquid injection rate and various boundary conditions on the heat transfer performance of the vapor chamber according to the thermal resistance network model, and constructs an objective function based on the effective heat diffusion area and the working fluid temperature. The thermal resistance network model of the vapor chamber is then iteratively updated according to the objective function, so that the thermal resistance network model can better restore the actual working process of the vapor chamber; a liquid level retreat sub-model is proposed to realize the prediction of the heat transfer performance of the vapor chamber under different heating powers; the model can be used to realize the rapid and accurate prediction of the heat transfer performance of the vapor chamber, and the entire prediction process only takes a few seconds, which greatly reduces the design cost and shortens the design cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a simplified cross-sectional schematic diagram of an application of a vapor chamber of the present invention.

[0051] Figure 2 It is a schematic diagram of a heat spreader thermal resistance network model of the present invention.

[0052] Figure 3 It is a schematic diagram of converting a rectangular area into a circular area of ​​equal area when solving the vapor diffusion thermal resistance according to the present invention.

[0053] Figure 4 The present invention is a schematic diagram of the steps of a method for predicting heat transfer performance of a vapor chamber based on a thermal resistance network model.

[0054] Figure 5 The figure is a flow chart of an implementation example of a method for predicting heat transfer performance of a vapor chamber based on a thermal resistance network model according to the present invention.

[0055] Figure 6 The figure is a flow chart of an implementation example of a system for predicting heat transfer performance of a vapor chamber based on a thermal resistance network model according to the present invention.

[0056] Figure 7 The figure is a schematic diagram of a software parameter input interface of an implementation example of a vapor chamber heat transfer performance prediction system based on a thermal resistance network model according to the present invention.

[0057] Figure 8 The figure is a schematic diagram of the software result output interface of an implementation example of a vapor chamber heat transfer performance prediction system based on a thermal resistance network model according to the present invention. DETAILED DESCRIPTION

[0058] The present invention is described in detail below in conjunction with the embodiments and drawings, but it should be understood that the embodiments and drawings are only used to exemplify the present invention and do not constitute any limitation on the protection scope of the present invention. All reasonable changes and combinations within the scope of the inventive concept of the present invention fall within the protection scope of the present invention.

[0059] In the description of the present invention, it should be noted that the structures, proportions, sizes, etc. shown in this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions under which the present invention can be implemented. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0060] At the same time, the terms such as "center", "lateral", "upper", "lower" and "one" cited in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments in their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0061] The present invention will be further described below in conjunction with the accompanying drawings.

[0062] For ease of understanding, this application first introduces the heat transfer process of the heat sink. Figure 1 As shown, a heat spreader structure and its positional relationship with a heat source and a heat sink are disclosed, wherein a heat source (9) is located below the heat spreader and contacts the evaporation end wall surface (8) of the heat spreader, and an isothermal convection heat transfer boundary (1) composed of a heat sink and an interface material is located above the heat spreader and contacts the condensation end wall surface (2) of the heat spreader; Figure 2 As shown, the heat emitted by the heat source (9) passes through the evaporation end wall (8) in the form of heat conduction, wherein a portion of the heat directly reaches the wick in the vertical direction, forming a corresponding heat conduction thermal resistance R p,e A small amount of heat diffuses along the evaporation end wall (8) to the surroundings and then reaches the wick in the vertical direction, forming a corresponding diffusion thermal resistance R s and thermal resistance R p,s After the heat passes through the evaporation end wall (8), part of the heat is transferred to the condensation end wall (2) through the support column (6) and the powder ring (4) by heat conduction, forming the support column heat conduction thermal resistance R r And the powder ring thermal conduction thermal resistance R sc The other part of the heat is conducted through the evaporation end wick (7) to form a heat conduction resistance R w,e Then the liquid working medium at the evaporation end absorbs heat and changes phase into steam, forming the evaporation phase change thermal resistance R eva , the steam quickly diffuses to the entire steam chamber (5), forming a steam diffusion thermal resistance R v The steam undergoes phase change at the condensation end liquid absorption core (3), condenses into liquid and releases heat, forming a condensation phase change thermal resistance R con (phase change thermal resistance of the heat source area at the condensation end), R con,n(Phase change thermal resistance of the non-heat source area at the condensation end) Finally, the heat passes through the condensation end wick (3) in the form of heat conduction, forming the thermal conduction thermal resistance R w,c (thermal conduction resistance of the heat source area at the condensation end), R w,c,n (thermal conduction resistance in the non-heat source area of ​​the condensation end); the heat from the two paths converges at the condensation end wall (2), and then passes through the condensation end wall (2) in the form of heat conduction to reach the radiator and the equivalent isothermal boundary (1) composed of the radiator and the interface material, forming the thermal conduction resistance R of the condensation end wall p,c (thermal conduction resistance of the heat source area on the condensation end wall), R p,c,n (Conduction thermal resistance of the non-heat source area on the condensation end wall); the heat sink and the equivalent isothermal boundary (1) composed of the heat sink and the interface material transfer heat to the outside through convection heat transfer, forming a convection heat transfer thermal resistance R lcp (heat source area convection heat transfer resistance), R lcp,n (Thermal resistance of convection heat transfer in non-heat source area).

[0063] Among them, the area corresponding to the heat source area is the heat source corresponding area, that is, the heat source area (10), the rest is the non-heat source area, and (11) is the effective heat diffusion area.

[0064] In a specific embodiment, the heat spreader thermal resistance network model is established based on the following assumptions, including: the heat spreader reaches a steady state; the physical properties of the wick are isotropic; the fluid flow is laminar and incompressible; and the evaporation / condensation phase change process of the working fluid only occurs at the interface between the liquid working fluid and the steam in the wick.

[0065] It should be noted that, unlike the prior art models which generally assume that the phase change process occurs at the interface between the steam and the wick, and that the interface is fixed and does not change, the model assumptions of the present application are more realistic.

[0066] In the above thermal resistance network model, the diffusion thermal resistance (R s ) is calculated using Cardoso's diffusion thermal resistance model, and the calculation formula is:

[0067]

[0068] η 2 -(2+α r )η+1=0

[0069]

[0070] in, α r , η are dimensionless parameters, R t,e is the total thermal resistance of the system after the evaporation end wall, R s is the diffusion thermal resistance, hp is the thickness of the evaporation end wall, k w is the thermal conductivity of the evaporation end wall, A e0 is the initial value of the effective heat diffusion area, A s is the heat source area, A e Calculated value of effective heat diffusion area.

[0071] It should be noted that the existing technology generally uses Lee's series thermal resistance model for the diffusion thermal resistance model, which cannot calculate the thermal diffusion area. Cardoso's diffusion thermal resistance model is a parallel thermal diffusion thermal resistance model, which can estimate the thermal diffusion area. This model is the basis for the application to use the heat source area as the evaporation area, liquid level change and other factors, and is also the calculation formula for judging whether the model converges. Calculate the support column R sc And pink ring R r When the heat conduction resistance is , the heat transfer area is the cross-sectional area of ​​the support column and powder ring in the heat source area.

[0072] Calculate the thermal resistance R of the wick at the evaporation end w,e and the evaporation end phase change thermal resistance R eva When , the calculated area is the area of ​​the heat source area minus the cross-sectional area of ​​the support column and powder ring in the area.

[0073] Calculate the heat conduction resistance R of the wick at the condensation end w,c , R w,c,n and condensation phase change thermal resistance R con , R con,n The calculated area is the area of ​​the condensation zone minus the cross-sectional area of ​​the support column and powder ring in this area.

[0074] It should be noted that this technical solution divides the heat source area and the non-heat source area, so as to determine the heat conduction and phase change area of ​​the support column, powder ring and evaporation end wick, which is different from the existing technology that generally does not consider the heat transfer process of the support column and powder ring, making the results of this model more accurate.

[0075] When calculating the thermal conduction resistance of the wick, the effective thermal conduction thickness is the thickness of the liquid working medium inside the wick, and the thickness of the liquid working medium is obtained according to a liquid surface retreat model based on a semi-experimental method.

[0076] In some specific embodiments, due to the different boundary conditions, the heat conduction process and phase change process of the wick at the evaporation end / condensation end of the heat spreader will undergo complex changes during actual operation, which can be simplified into the change in the liquid level height inside the wick at the evaporation end / condensation end, while satisfying the following assumptions.

[0077] Affected by the difference in capillary force between the evaporation end wick and the condensation end wick, when the heat source power is 0W, the initial height h0 of the liquid working medium inside the wick is determined, the wick with large capillary force and the powder ring are filled with liquid working medium, while the wick with small capillary force is not filled with liquid working medium.

[0078] The area where the liquid level of the liquid working medium in the evaporation end wick is lowered is the area corresponding to the heat source, and the area where the liquid level of the liquid working medium in the condensation end wick is raised is the entire condensation end wick area.

[0079] According to the law of conservation of mass, the mass reduction of the liquid working medium in the evaporation end wick is equal to the mass increase of the liquid working medium in the condensation end wick.

[0080] Assuming that a buffer time Δt is required for the liquid level change of the liquid working medium inside the evaporation end / condensation end wick to reach a steady state, the liquid level change of the liquid working medium inside the evaporation end / condensation end wick can be calculated according to the following formula:

[0081]

[0082] Wherein, Δh is the liquid level change, Q is the heat source power, ρ l is the density of the working fluid, ε is the porosity of the wick, A l is the area of ​​the liquid level change region, the evaporation end is the area corresponding to the heat source, the condensation end is the entire condensation end liquid absorption core area, and Δt is the buffer time, which is obtained through experiments.

[0083] The thickness of the liquid working medium inside the wick at the evaporation end is: h=h0-Δh;

[0084] The thickness of the liquid working medium inside the liquid wick at the condensation end is: h=h0+Δh.

[0085] In the above-mentioned heat spreader thermal resistance network model, the calculation formula for thermal conduction resistance is:

[0086]

[0087] Where R is the thermal resistance of heat conduction through the structure, h is the thickness of the structure along the heat transfer direction, k is the thermal conductivity of the structure, and A is the heat conduction area of ​​the structure perpendicular to the heat transfer direction.

[0088] In the vapor chamber thermal resistance network model, the calculation formulas for the evaporation phase change thermal resistance and the condensation phase change thermal resistance are:

[0089]

[0090] Among them, R pt is the phase change thermal resistance, α is the adjustment coefficient, R gas is the gas constant of water vapor, Tv is the saturated steam temperature of the working fluid, A pt is the phase change area, h fg is the latent heat of vaporization of the working fluid, P v is the saturated vapor pressure of the working fluid, because T v 、h fg and P v It changes with the working fluid temperature, so the phase change thermal resistance is different when the working fluid temperature is different.

[0091] Calculate the vapor diffusion thermal resistance (R v ) The influence of the support column and the powder ring on the steam flow is ignored during the calculation. The calculation formula for the steam diffusion thermal resistance is:

[0092]

[0093] Among them, Q eva is the power transferred by phase change, ΔP v is the pressure drop caused by steam flow. Since the heat source is located at the center of the vapor chamber, to facilitate the calculation of the steam diffusion thermal resistance, Figure 3 As shown, the steam chamber area and the heat source area are converted into circular areas of equal area. Assuming that the diffusion boundary of the steam diffusion process is circular and diffuses uniformly to the surroundings, the ΔP v It is obtained by integrating the circular area, and the calculation formula is:

[0094]

[0095] Among them, r p is the radius of the circular region of equal area in the steam chamber, r e is the radius of the circular region of equal area of ​​the heat source, h v is the thickness of the steam chamber, the diffusion boundary can be regarded as a rectangle after expansion, P o is the Poiseuille number, because μ v and ρ v It changes with the change of working fluid temperature, so the steam diffusion thermal resistance value is different when the working fluid temperature is different. When the cross section of the saturated steam diffusion channel is rectangular, P o Calculate using the following formula:

[0096]

[0097] Among them, w v is the circumference of the circle where the diffusion boundary lies.

[0098] For the isothermal convection heat transfer boundary, the convection heat transfer thermal resistance calculation formula is:

[0099]

[0100] Among them, R hs is the convective heat transfer resistance, A we is the wall area of ​​the condensation end, h sp is the equivalent convection heat transfer coefficient of the isothermal convection heat transfer boundary.

[0101] like Figure 5 As shown in the figure, when the effective heat diffusion area A of the evaporation end wall is calculated e and saturated steam temperature T v ; After that, the heat spreader thermal resistance network model is iterated, specifically (steps S1-S3 are consistent with the above).

[0102] S1. Determine the boundary conditions and set the initial value A of the effective heat diffusion area of ​​the evaporation end wall e0 and the initial value of saturated steam temperature T v0 ;

[0103] S2. Constructing the heat spreader thermal resistance network model and calculating the thermal resistance of each component;

[0104] S3. Calculate the heat spreader thermal resistance network model constructed in step S2 according to the boundary conditions to obtain the effective heat diffusion area A of the evaporation end wall e and saturated steam temperature T v ;

[0105] S4. Determine the effective heat diffusion area A of the evaporation end wall according to the following inequality e Whether the result converges:

[0106]

[0107] If it does not converge, then A e Assign the value of to A e0 , and return to step S2 to update the vapor chamber thermal resistance network model and calculate the thermal resistance of each component again;

[0108] S5. Determine the saturated steam temperature T according to the following inequality v Is the result convergent:

[0109] |T v0 -T v |<0.05;

[0110] If it does not converge, T v Assign the value of v0 , and return to step S2 to update the heat spreader thermal resistance network model and calculate the thermal resistance of each component again. If the result converges, calculate the temperature difference and the transferred power at both ends of the thermal resistance of each component, and set the maximum number of loop iterations to 50 times;

[0111] S6. Calculate the heat transfer performance of the vapor chamber according to the resistance value, temperature difference and transfer power of each component of the vapor chamber thermal resistance network model outputted in S5.

[0112] like Figure 6 As shown, a vapor chamber heat transfer performance prediction system based on a thermal resistance network model is provided. Based on the above vapor chamber heat transfer performance prediction method based on a thermal resistance network model, the following steps are adopted to realize the automation of vapor chamber heat transfer performance prediction:

[0113] S1. Parameter acquisition module, used to obtain the heat spreader structure parameters and boundary condition parameters from the outside, and perform data preprocessing, including: checking the correctness and accuracy of the data, including checking whether there is data missing, checking whether the sum of the wall thickness and the wick thickness exceeds the total thickness of the heat spreader, whether the wick porosity exceeds 100%, whether the total area of ​​the support column and the powder ring exceeds the area of ​​the heat spreader, and whether the diameter of the support column and the powder ring exceeds the horizontal spacing and the vertical spacing;

[0114] S2. The thermal resistance network module obtains the required parameters from the parameter acquisition module, constructs the vapor chamber thermal resistance network model, and updates the vapor chamber thermal resistance network model according to the values ​​of the effective heat diffusion area of ​​the evaporation end wall and the saturated steam temperature returned by the prediction module;

[0115] S3. A prediction module, which calculates the temperature difference at both ends of each component thermal resistance, the transferred power and the heat transfer performance of the vapor chamber, and generates a bar graph based on the results;

[0116] S4. Data storage module, saves the result bar graph in .png format, writes the data related to the structure parameters, boundary condition parameters and heat transfer performance prediction results of the heat spreader into an Excel document, and saves it to a specified path;

[0117] S5. Result display module, outputs and displays the heat transfer performance prediction results of the heat spreader.

[0118] Example 1 Prediction of heat transfer performance of vapor chamber

[0119] Based on the heat transfer performance prediction system of the heat spreader based on the thermal resistance network model of the present invention, a heat spreader heat transfer performance prediction system software tool is written using C++ and QT. The schematic diagram of the parameter input interface is shown in FIG. Figure 7 As shown. You can switch to different parameter input interfaces through the navigation button below. After entering the required parameters for the performance prediction of the vapor chamber in the parameter input interface, click the calculation button to predict the corresponding vapor chamber heat transfer performance. The schematic diagram of the prediction result output interface is shown as follows Figure 8As shown, you can view the heat transfer performance of the heat spreader, the thermal resistance of each component, the transferred power and the temperature difference at both ends. Slide the interface down to view the thermal resistance bar graph of each component and the transferred power bar graph, which is convenient for engineers to intuitively view various data and optimize.

[0120] In this embodiment, the required parameter data for predicting the performance of the vapor chamber is listed in Table 1.

[0121] Table 1

[0122]

[0123] Through the heat transfer performance prediction system of the vapor chamber based on the thermal resistance network model provided in this embodiment, the corresponding heat transfer performance result data of the vapor chamber are predicted as shown in Table 2.

[0124] Table 2

[0125]

[0126] According to the above-mentioned prediction parameter data of the performance of the heat spreader, the heat spreader samples were manufactured and the heat transfer performance of the heat spreader was tested. The water-cooled plate was placed on the top of the heat spreader and the heated copper block was placed on the bottom. The three were pressed against each other by a cylinder, and the contact interface was coated with thermal grease. Five T-type thermocouples were arranged on the evaporation end and the condensation end of the heat spreader for temperature measurement. A thermocouple was arranged in the center of each surface as the center temperature. Four thermocouples were arranged at the four corners 10mm away from the side, and the average value was taken as the temperature around the surface. The final heat spreader test results are well consistent with the predicted results. The overall thermal resistance error of the heat spreader is about 8%, and the errors of the center temperature of the evaporation end wall, the temperature difference between the center of the evaporation end wall and the surroundings, and the temperature difference between the center of the condensation end wall and the surroundings are all less than 1°C.

[0127] The above embodiments are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for predicting heat transfer performance of a vapor chamber based on a thermal resistance network model, characterized in that: The following steps are involved: S1. Determine the boundary conditions, including the heat source size, heat source power, radiator equivalent heat transfer coefficient and ambient temperature; set the initial value A of the effective heat diffusion area of ​​the evaporation end wall of the heat spreader e0 A is the heat source area s , that is, A e0 =A s , set the initial value of saturated steam temperature T v0 is the radiator fluid inlet temperature T in , that is, T v0 =T in ; S2. Construct a heat spreader thermal resistance network model and calculate the thermal resistance of each component; S3. Calculate the heat spreader thermal resistance network model constructed in step S2 according to the heat spreader boundary conditions to obtain the effective heat diffusion area A of the evaporation end wall e and saturated steam temperature T v ; S4. According to the calculated value of the effective heat diffusion area of ​​the evaporation end wall and the saturated steam temperature, the heat spreader thermal resistance network model is iterated: the effective heat diffusion area A of the evaporation end wall is determined. e and saturated steam temperature T v Whether the result converges, if not, then A e Assign the value of to A e0 , T v Assign the value of v0 , and return to step S2 to update the vapor chamber thermal resistance network model and calculate the thermal resistance of each component again. If the result converges, calculate the temperature difference and the transferred power at both ends of the thermal resistance of each component; S5. According to the iteration result of the vapor chamber network model outputted from S4, the resistance value, temperature difference and transfer power of each component of the vapor chamber thermal resistance network model are obtained, and the heat transfer performance of the vapor chamber is calculated; The heat spreader thermal resistance network model is based on the following assumptions: the evaporation / condensation phase change process of the working fluid only occurs at the interface between the liquid working fluid and the steam in the wick, and the height of the interface changes with the change of the heating power.

2. The prediction method according to claim 1, characterized in that: The construction of the vapor chamber thermal resistance network model specifically includes: analyzing the heat transfer process of the vapor chamber and selecting a heat transfer structure to determine the thermal resistance formed during the heat transfer process, including: Evaporation end wall heat conduction resistance R p,e :Heat is generated through the evaporation end wall by heat conduction; Thermal resistance R s : It is formed on the evaporation end wall because the heat source area is smaller than the heat plate area; Evaporation end diffusion heat conduction thermal resistance R p,s : After the heat diffuses along the plane of the evaporation end wall, it is formed through the evaporation end wall by heat conduction; Support column thermal resistance R sc And powder ring thermal resistance R r :The heat is generated by heat conduction through the support column and the powder ring; Thermal resistance R of the wick heat conduction at the evaporation end w,e :Heat is generated by heat conduction through the evaporation end wick; Evaporation end phase change thermal resistance R eva : The liquid working medium at the evaporation end absorbs heat and changes phase to vaporize into steam; Vapor diffusion thermal resistance R v :The steam quickly diffuses to form the entire steam chamber; Condensation phase change thermal resistance: The vapor diffuses to the condensation end liquid absorption core to undergo phase change and condense into liquid, including the phase change thermal resistance R of the condensation end heat source area. con and the phase change thermal resistance R of the non-heat source area at the condensation end con,n ; Thermal conduction resistance of the condensation end wick: Heat is formed by heat conduction through the condensation end wick, including the thermal conduction resistance R of the condensation end heat source area wick w,c and the heat conduction resistance R of the liquid absorption core in the non-heat source area at the condensation end w,c,n ; Condensation end wall heat conduction thermal resistance: Heat gathers on the condensation end wall, and then passes through the condensation end wall to the radiator by heat conduction, including the condensation end heat source area wall heat conduction thermal resistance R p,c and the heat conduction resistance R of the non-heat source area wall at the condensation end p,c,n ; Convective heat transfer thermal resistance: The heat sink transfers heat to the outside world through convection heat transfer, including the interface thermal resistance between the heat sink and the heat sink and the heat sink thermal resistance, including the convection heat transfer thermal resistance R of the heat source area lcp , non-heat source area convection heat transfer thermal resistance R lcp,n .

3. The prediction method according to claim 2, characterized in that: The diffusion thermal resistance formed on the evaporation end wall surface is calculated using Cardoso's diffusion thermal resistance model.

4. The prediction method according to claim 2, characterized in that: The heat source area and the non-heat source area are determined according to the size of the heat source. The support columns and powder rings in the heat source area participate in the heat transfer process of the heat spreader and heat conduction occurs. The heat conduction area and the evaporation phase change area of ​​the evaporation end wick are: the heat source area minus the cross-sectional area of ​​the support columns and powder rings in the heat source area.

5. The prediction method according to claim 2, characterized in that: The calculation formula of the thermal conduction resistance is: ; Where R is the heat conduction resistance of the heat through the structure, h is the thickness of the heat through the structure along the heat transfer direction, k is the thermal conductivity of the heat through the structure, and A is the heat conduction area of ​​the heat through the structure on the cross section perpendicular to the heat transfer direction; Among them, the thermal conduction resistance includes: the thermal conduction resistance of the evaporation end wall 、 Thermal resistance R of the wick heat conduction at the evaporation end w,e、 The thermal conduction resistance of the liquid absorption core at the condensation end and the thermal conduction resistance of the wall at the condensation end.

6. The prediction method according to claim 5, characterized in that: In the heat conduction resistance of the evaporation end wick and the heat conduction resistance of the condensation end wick, the thickness h along the heat transfer direction is the thickness of the liquid working medium inside the wick, which is obtained according to a liquid surface retreat model based on a semi-experimental method, specifically: According to the liquid filling rate of the vapor chamber and the difference in capillary force between the evaporation end wick and the condensation end wick, the initial height h0 of the liquid working medium inside the wick is determined, the wick with large capillary force and the powder ring are filled with liquid working medium, while the wick with small capillary force is not filled with liquid working medium; Calculate the change in the liquid level of the liquid working medium inside the wick: ; Where Δh is the change in liquid level, Q is the power of the heat source, and h fg is the latent heat of vaporization of the working fluid, ρ l is the density of the working fluid, ε is the porosity of the wick, A l is the area of ​​the liquid level change region, the evaporation end is the area corresponding to the heat source, the condensation end is the entire condensation end liquid absorption core area, and Δt is the buffer time, which is obtained through experiments; The thickness of the liquid working medium inside the wick at the evaporation end is: ; The thickness of the liquid working medium inside the wick at the condensation end is: .

7. The prediction method according to claim 1, characterized in that: Using inequality Determine the effective heat diffusion area A of the evaporation end wall e Whether the result converges, if not, then A e Assign the value of to A e0 , and return to step S2 to update the heat spreader thermal resistance network model and recalculate the thermal resistance of each component: Determine the saturated steam temperature T v Whether the result converges, if not, T v Assign the value of v0 , and return to step S2 to update the vapor chamber thermal resistance network model and calculate the thermal resistance of each component again. If the result converges, calculate the temperature difference and the transferred power at both ends of the thermal resistance of each component; The maximum number of loop iterations is set to 50.

8. The prediction method according to claim 1, characterized in that: The heat transfer performance of the vapor chamber includes: the overall thermal resistance of the vapor chamber, the central temperature of the evaporation end wall, the temperature difference between the central and surrounding areas of the evaporation end wall, and the temperature difference between the central and surrounding areas of the condensation surface wall.

9. A prediction system for a vapor chamber heat transfer performance prediction method based on the thermal resistance network model of claim 1, characterized in that: include: S1. Parameter acquisition module, used to obtain heat spreader structure parameters and boundary condition parameters from the outside and perform data preprocessing; S2. The thermal resistance network module obtains the required parameters from the parameter acquisition module, constructs the vapor chamber thermal resistance network model, and updates the vapor chamber thermal resistance network model according to the values ​​of the effective heat diffusion area of ​​the evaporation end wall and the saturated steam temperature returned by the prediction module; S3. A prediction module, which calculates the temperature difference at both ends of each component thermal resistance, the transferred power and the heat transfer performance of the vapor chamber, and generates a bar graph based on the results; S4. Data storage module, saves the result bar graph in .png format, writes the data related to the structure parameters, boundary condition parameters and heat transfer performance prediction results of the heat spreader into an Excel document, and saves it to a specified path; S5. Result display module, outputs and displays the heat transfer performance prediction results of the heat spreader.

Images