A method for predicting thermal resistance of layered composite wick vapor chamber

Abstract

The present invention discloses a method for predicting the thermal resistance of a layered composite wick vapor chamber, comprising: dividing the layered composite wick into several layers, obtaining the calculation parameters of each layer of the wick; comprehensively considering the liquid filling rate and the heating power to determine the effective heat conduction thickness of each layer of the wick; analyzing the series-parallel relationship of the heat conduction part of the layered composite wick, and on this basis constructing a vapor chamber thermal resistance network model to predict the thermal resistance of the layered composite wick vapor chamber. The present invention focuses on the design process of the layered composite wick vapor chamber, solves the problem that the traditional prediction method is difficult to predict the thermal resistance of the layered composite wick vapor chamber, and can only be determined by processing samples and multiple experimental measurements, which can greatly improve the design efficiency and reduce the cost of the verification process.

Description

Technical Field

[0001] The invention relates to the technical field of vapor chamber design, and in particular to a method for predicting the thermal resistance of a layered composite liquid wick vapor chamber. Background Art

[0002] Traditional single-structure wicks are gradually unable to meet the needs of high heat flux density in actual applications of vapor chambers. The wicks are developing towards a multi-dimensional composite design with axial segmentation, radial stratification, and coordinated proportions. Layering and compounding wicks with different geometric structures, pore sizes, permeabilities, capillary forces, and thermal conductivity can effectively coordinate the conflict between permeability and capillary forces, increase the maximum power of the vapor chamber, and reduce the thermal resistance of the vapor chamber. However, the parameters of the vapor chamber are complex, and the performance is affected by the structural parameters. The layered compounding of wicks further increases the difficulty of predicting the thermal resistance of the vapor chamber.

[0003] At present, the method for predicting the thermal resistance of the heat spreader is mainly numerical analysis, but they are all for a single structure of the liquid absorbent core. There is no method to predict the thermal resistance of the heat spreader with a layered composite structure of the liquid absorbent core. If the traditional method is still used, it is necessary to make samples and conduct multiple experiments for measurement. Due to the large number of parameters of the heat spreader with a layered composite structure of the liquid absorbent core, it is difficult to make a comprehensive consideration during the design process of the heat spreader, resulting in the thermal resistance of the heat spreader failing to meet the use requirements. Therefore, in the traditional design and manufacturing process of the heat spreader with a layered composite liquid absorbent core, it is highly dependent on the experience of engineers, and through multiple experiments and repeated iterative optimization, the thermal resistance of the heat spreader can meet the use requirements, which is not only costly but also inefficient. Summary of the invention

[0004] In order to solve the technical problems existing in the background technology, the present invention aims to provide a thermal resistance network modeling method. The established thermal resistance network model can restore the layered composite absorbent core and realize the accurate prediction of the thermal resistance of the layered composite absorbent core heat sink.

[0005] In order to solve the above problems, the technical solution of the present application discloses a method for predicting the thermal resistance of a layered composite wick vapor chamber, such as Figure 1 As shown, the following steps are included:

[0006] S1: Obtain the calculation parameters of each layer of wick in the vapor chamber;

[0007] S2: Determine the initial effective thickness of each layer of the wick according to the liquid filling rate of the vapor chamber;

[0008] S3: Determine the effective heat conduction thickness of each layer of the wick according to the heating power;

[0009] S4: Analyze the series-parallel relationship of the thermal conductive parts of the layered composite absorbent core and establish a thermal resistance network model of the layered composite absorbent core;

[0010] S5: constructing a vapor chamber thermal resistance network model to predict the overall thermal resistance of the layered composite wick vapor chamber;

[0011] The heat spreader is a layered composite liquid absorbent core heat spreader, and the liquid absorbent core at the evaporation end or the condensation end thereof is composed of two or more liquid absorbent cores with different parameters in a layered composite manner in the radial direction.

[0012] Furthermore, the radial direction of the layered composite wick is: perpendicular to the copper plate at that location, from the wall to the steam chamber; the basis for judging the stratification is: the type of wick, coverage area, pore size, wick porosity or equivalent thermal conductivity are different. The existing technology mainly stays at the stage of different types of wicks in the upper and lower base wicks for judging the stratification of wicks. The present application uses the difference in wick type, coverage area, pore size, wick porosity or equivalent thermal conductivity as the basis for judging the stratification of wicks, thereby involving a wider range of wick stratification composites. It is not only for wick types, but also for wicks of the same type but with different coverage areas, different structural parameters or different equivalent thermal conductivities. They will also be regarded as layered composite wicks, thereby making the predicted types of layered composite wicks more numerous and the predicted results more accurate. Furthermore, the calculation parameters of each layer of wicks include: wick thickness h w , Liquid wick area A w , the heat transfer area of ​​the wick covers an area A s , the wick porosity ε and the wick equivalent thermal conductivity k w ; The heat transfer area of ​​the wick is very large because the heat conduction resistance of the wick along the plane direction is extremely large, and the heat propagation in this direction can be ignored. Therefore, the heat transfer area of ​​the wick at the evaporation end is the heat source area. After the diffusion of steam, the heat is evenly transferred to the entire surface of the wick at the condensation end. The heat transfer area of ​​the wick at the condensation end is the entire wick area at the condensation end.

[0013] Furthermore, the method for determining the initial effective thickness of each layer of the absorbent core is: determining the volume of the liquid working medium according to the liquid filling rate of the heat plate of the layered composite absorbent core, and calculating the initial effective thickness of each layer of the absorbent core in descending order of the capillary pressure according to the capillary pressure of the absorbent core, as shown in the following formula:

[0014]

[0015] In the formula, h 0i is the initial effective thickness of the wick calculated for the i-th time, h wi is the thickness of the wick calculated for the i-th time, V li To calculate the remaining liquid volume of the i-th wick, V wi is the pore volume of the wick calculated for the i-th time.

[0016] Furthermore, the step of determining the effective heat conduction thickness of each layer of the absorbent core includes:

[0017] (1) The liquid transfer volume in the wick is calculated according to the heating power and liquid level retreat method, as shown in the following formula:

[0018]

[0019] Where V t is the volume of the transferred liquid, Q is the heating power, Δt is the buffer time, which can be obtained by testing with an existing vapor chamber, and h fg is the latent heat of phase change, ρ l is the density of the working fluid;

[0020] (2) According to the liquid transfer volume, the effective heat transfer thickness of the evaporation end wick is calculated in sequence from the steam chamber to the wall surface, as shown in the following formula:

[0021]

[0022] Where V ti To calculate the remaining volume of the transferred liquid at the i-th wick, V 0i To calculate the initial liquid volume inside the i-th wick, h ei is the effective heat transfer thickness of the wick at the evaporation end, A si is the coverage area of ​​the heat transfer region of the i-th wick;

[0023] (3) According to the liquid transfer volume, the effective heat transfer thickness of the condensation end wick is calculated in sequence from the steam chamber to the wall surface, as shown in the following formula:

[0024]

[0025] In the formula, h ci is the effective heat transfer thickness of the ith wick calculated at the condensation end.

[0026] The existing technology mainly treats the wick at the stage of setting the wick to be filled with liquid working fluid, and the liquid level and the thermal conductivity of the wick remain unchanged. In the actual layered wick, as the heat flux density of the heat source increases, the liquid level inside the wick at the evaporation end decreases, and the liquid level inside the wick at the condensation end increases, resulting in changes in the state of the wick participating in the heat conduction process at some levels, thus resulting in large errors. The present application provides a method for calculating the change of the liquid level inside the wick, which is closer to the change process of the liquid level inside the layered composite wick under different heat flux densities, so the prediction result is more accurate.

[0027] Furthermore, the series-parallel relationship judgment basis of the thermal resistance network model of the absorbent core is: according to the covering relationship between two adjacent layers of the absorbent core, the absorbent core is divided into a covered area and a non-covered area, the thermal resistance of two adjacent layers of the absorbent core in the covered area is in a series relationship, and the heat conduction path of the absorbent core in the non-covered area is in a parallel relationship with the heat conduction path of the absorbent core in the covered area.

[0028] The prior art has not yet provided a method for dealing with the situation where two adjacent layers of absorbent cores are not fully covered. The present application analyzes the series-parallel relationship between the layered composite absorbent cores, provides a method for establishing a thermal resistance network for the situation where two adjacent layers of absorbent cores are not fully covered, and expands the predicted types of layered composite absorbent cores.

[0029] Furthermore, the layered composite wick vapor chamber thermal resistance network comprises:

[0030] Evaporation end wall heat conduction resistance R p,e :Heat is generated through the evaporation end wall by heat conduction;

[0031] Thermal resistance of heat conduction of the evaporation end wick: Heat is formed by heat conduction through the evaporation end layered composite wick thermal resistance network;

[0032] Phase change thermal resistance at the evaporation end: Heat is formed on the surface of the evaporation end wick through the layered composite wick thermal resistance network at the evaporation end;

[0033] Phase change thermal resistance at the condensation end: heat reaches the surface of the condensation end wick through vapor diffusion, and vapor condenses on the entire surface of the condensation end wick;

[0034] Thermal resistance of heat conduction of the condensing end wick: Heat is formed by heat conduction through the condensing end layered composite wick thermal resistance network;

[0035] Condensation end wall heat conduction thermal resistance R p,c :Heat is generated through the evaporation end wall by heat conduction.

[0036] Furthermore, when calculating the thermal conduction resistance of the evaporation end wall and the evaporation phase change resistance, the heat transfer area is the area corresponding to the heat source.

[0037] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0038] The present invention focuses on the design process of a vapor chamber of a layered composite wick. By analyzing the heat transfer process of the layered composite wick, a thermal resistance network model is adopted to establish the relationship between the required parameters of the layered composite wick and the thermal resistance of the vapor chamber. This solves the problem that, during the design process of the vapor chamber of the layered composite wick, the thermal resistance can only be determined by processing samples and performing multiple experimental measurements. This can greatly improve the design efficiency and reduce the cost of the verification process. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of the steps of a method for predicting the thermal resistance of a layered composite vapor chamber core of the present invention;

[0040] Figure 2 A schematic diagram of the structure of a layered composite vapor chamber according to an implementation example of a method for predicting thermal resistance of a layered composite vapor chamber according to the present invention;

[0041] Figure 3 A schematic diagram of the structure of a layered composite absorbent core according to an implementation example of a method for predicting thermal resistance of a vapor chamber of a layered composite absorbent core according to the present invention;

[0042] Figure 4 The figure is a schematic diagram of a thermal resistance network model according to an implementation example of a method for predicting the thermal resistance of a layered composite vapor chamber according to the present invention. DETAILED DESCRIPTION

[0043] 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.

[0044] 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.

[0045] 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.

[0046] The present invention will be further described below in conjunction with the accompanying drawings.

[0047] As shown in FIG. 2, a specific layered composite wick vapor chamber is disclosed, wherein the heat source and the heat sink are arranged on both sides of the vapor chamber, the wick at the evaporation end is a layered composite wick, the bottom layer is covered with 200-mesh copper powder sintered wick, the top layer is a 150-mesh wire mesh sintered wick, the wire mesh sintered wick is not covered with the heat source area, and the condensation end is a 100-mesh wire mesh sintered wick. Predicting the thermal resistance of the layered composite wick vapor chamber includes the following steps:

[0048] Step S1, dividing the absorbent core into several layers, and obtaining calculation parameters of each layer of the absorbent core;

[0049] Step S2, determining the initial effective thickness of each layer of the wick according to the liquid filling rate of the vapor chamber;

[0050] Step S3, determining the effective heat conduction thickness of each layer of the wick according to the heating power;

[0051] Step S4, analyzing the series-parallel relationship of the heat-conducting parts of the layered composite absorbent core, and establishing a thermal resistance network model of the absorbent core;

[0052] Step S5, constructing a vapor chamber thermal resistance network model to predict the overall thermal resistance of the vapor chamber.

[0053] As shown in Figure 3, the evaporation end wick can be divided into a bottom layer and a top layer according to the type of wick. The bottom layer is a 200-mesh copper powder sintered wick, and the top layer is a 150-mesh wire mesh sintered wick.

[0054] Furthermore, the heat transfer area of ​​the wick is determined. Since the heat conduction resistance of the wick along the plane direction is extremely large, the propagation of heat in this direction can be ignored. Therefore, the heat transfer area of ​​the wick at the evaporation end is the heat source area. After the diffusion of steam, the heat is evenly transferred to the entire surface of the wick at the condensation end. The heat transfer area of ​​the wick at the condensation end is the entire wick area at the condensation end.

[0055] Therefore, the calculation parameters of the 200 mesh copper powder sintered liquid absorbent core include: the liquid absorbent core thickness h w1 , Liquid wick area A w1 , the heat transfer area of ​​the wick covers an area A s , the wick porosity ε1 and the wick equivalent thermal conductivity k w1 ; The 150 mesh sintered liquid wick: the liquid wick thickness h w2 , Liquid wick area A w2 , the heat transfer area of ​​the wick covers an area A s / 2, the wick porosity ε2 and the wick equivalent thermal conductivity k w2 ; The 100 mesh sintered liquid wick: the liquid wick thickness h w3 , Liquid wick area A w1 , the heat transfer area of ​​the wick covers an area A w1 , the wick porosity ε3 and the wick equivalent thermal conductivity k w3 .

[0056] Further, the initial effective thickness of each layer of the wick is determined, the volume of the liquid working medium is determined according to the liquid filling rate of the soaking plate, and the initial effective thickness of the wick is calculated in descending order according to the capillary pressure of the wick. The capillary force is ranked from large to small as follows: 200-mesh copper powder sintered wick, 150-mesh wire mesh sintered wick, and 100-mesh wire mesh sintered wick. The specific calculation is shown in the following formula:

[0057]

[0058] In the formula, h 0i is the initial effective thickness of the wick calculated for the i-th time, h wi is the thickness of the wick calculated for the i-th time, V li To calculate the remaining liquid volume of the i-th wick, V wi is the pore volume of the wick calculated for the i-th time.

[0059] Further, determining the effective heat conduction thickness of each layer of the wick comprises the following steps:

[0060] (1) The liquid transfer volume in the wick is calculated according to the heating power and liquid level retreat method, as shown in the following formula:

[0061]

[0062] Where Vt is the volume of the transferred liquid, Q is the heating power, Δt is the buffer time, which can be obtained by testing the existing heat sink, and h fg is the latent heat of phase change, ρ l is the density of the working fluid;

[0063] (2) According to the liquid transfer volume, the effective heat transfer thickness of the evaporation end wick is calculated in sequence from the steam chamber to the wall surface, that is, the effective heat transfer thickness of the wick sintered with a 150-mesh screen is calculated first, and then the effective heat transfer thickness of the wick sintered with a 200-mesh copper powder is calculated, as shown in the following formula:

[0064]

[0065] Where V ti To calculate the remaining volume of the transferred liquid at the i-th wick, V 0i To calculate the initial liquid volume inside the i-th wick, h ei is the effective heat transfer thickness of the wick at the evaporation end, A si is the coverage area of ​​the heat transfer region of the i-th wick;

[0066] (3) According to the liquid transfer volume, the effective heat transfer thickness of the condensation end wick is calculated in sequence from the steam chamber to the wall surface, as shown in the following formula:

[0067]

[0068] In the formula, h ci is the effective heat transfer thickness of the ith wick calculated at the condensation end.

[0069] Furthermore, the series-parallel relationship of the thermal resistance network model of the absorbent core is determined, and the heat transfer area is divided into a covered area and a non-covered area according to the coverage relationship of the 150-mesh wire mesh sintered absorbent core to the 200-mesh copper powder sintered absorbent core. The thermal conduction resistance of the 200-mesh copper powder sintered absorbent core in the covered area is connected in series with the 150-mesh wire mesh sintered absorbent core, and the total thermal resistance thereof is connected in parallel with the thermal conduction resistance of the 200-mesh copper powder sintered absorbent core in the non-covered area.

[0070] Further, such as Figure 4 As shown, the layered composite liquid wick vapor chamber thermal resistance network includes:

[0071] The heat first passes through the heat conduction resistance of the evaporation end wall, and then passes through the layered composite wick thermal resistance network of the evaporation end, forming an evaporation phase change thermal resistance on the wick surface of the evaporation end.

[0072] The heat reaches the surface of the condensation end wick through steam diffusion, and the steam condenses on the entire surface of the condensation end wick to form a condensation phase change thermal resistance, followed by the heat conduction thermal resistance of the condensation end wick, and finally through the heat conduction thermal resistance of the condensation end wall.

[0073] Furthermore, when calculating the thermal conduction resistance of the evaporation end wall, since the diffusion thermal resistance of the evaporation end wall along the planar direction is extremely large, the propagation of heat along the planar direction can be ignored. Therefore, when calculating the thermal conduction resistance of the evaporation end wall and the evaporation phase change thermal resistance, the heat transfer area is the area corresponding to the heat source.

[0074] In this embodiment, the thermal resistance prediction parameters of the vapor chamber of the layered composite liquid absorbent core are listed in Table 1.

[0075] Table 1

[0076]

[0077] The parameter data of the layered composite wick for predicting the thermal resistance of the vapor chamber are listed in Table 2.

[0078] Table 2

[0079]

[0080] According to the thermal resistance prediction method of a layered composite liquid-absorbing core soaking plate provided in this embodiment, the corresponding thermal resistance of the soaking plate is predicted to be 0.0157K / W. The soaking plate sample is manufactured according to the above-mentioned soaking plate parameter data, and the thermal resistance test of the soaking plate is carried out. The soaking plate is a water-cooled plate above and a heated copper block below. The three are pressed against each other by a cylinder, and the contact interface is coated with thermal conductive silicone grease. A thermocouple is arranged at the center of the surface of the evaporation end and the condensation end of the soaking plate, respectively, as the center temperature. The difference between the center temperatures of the two surfaces divided by the heating power of the heat source is the corresponding thermal resistance test result of the layered composite liquid-absorbing core soaking plate. The final average thermal resistance of the soaking plate test result is about 0.0146K / W, which is in good consistency with the predicted result.

[0081] 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 the thermal resistance of a layered composite wick vapor chamber, characterized in that: The steps include: S1: Obtain the calculation parameters of each layer of wick in the vapor chamber; S2: Determine the initial effective thickness of each layer of the wick according to the liquid filling rate of the vapor chamber; S3: Determine the effective heat conduction thickness of each layer of the wick according to the heating power; S4: Analyze the series-parallel relationship of the thermal conductive parts of the layered composite absorbent core and establish a thermal resistance network model of the layered composite absorbent core; S5: constructing a vapor chamber thermal resistance network model to predict the overall thermal resistance of the layered composite wick vapor chamber; The heat spreader is a layered composite liquid absorbent core heat spreader, and the liquid absorbent core at the evaporation end or the condensation end thereof is composed of two or more liquid absorbent cores with different parameters in a layered composite manner in the radial direction; Wherein, the thermal resistance network model of the layered composite liquid wick vapor chamber includes: Evaporation end wall heat conduction resistance R p,e :Heat is generated through the evaporation end wall by heat conduction; Thermal resistance of heat conduction of the evaporation end wick: Heat is formed by heat conduction through the evaporation end layered composite wick thermal resistance network; Phase change thermal resistance at the evaporation end: Heat is formed on the surface of the evaporation end wick through the layered composite wick thermal resistance network at the evaporation end; Phase change thermal resistance at the condensation end: heat reaches the surface of the condensation end wick through vapor diffusion, and vapor condenses on the entire surface of the condensation end wick; Thermal resistance of heat conduction of the condensing end wick: Heat is formed by heat conduction through the condensing end layered composite wick thermal resistance network; Condensation end wall heat conduction thermal resistance R p,c :Heat is generated through the evaporation end wall by heat conduction.

2. The prediction method according to claim 1, characterized in that: The radial direction of the layered composite liquid absorbent core is perpendicular to the copper plate at that location and points from the wall surface to the steam cavity. The basis for judging the layering is that the liquid absorbent core types, coverage areas, pore sizes, liquid absorbent core porosity or equivalent thermal conductivity are different.

3. The prediction method according to claim 1, characterized in that: The calculation parameters of each layer of the absorbent core include: the thickness of the absorbent core h w , Liquid wick area A w , the heat transfer area of ​​the wick covers an area A s , the wick porosity ε and the wick equivalent thermal conductivity k w .

4. The prediction method according to claim 1, characterized in that: The method for determining the initial effective thickness of each layer of the absorbent core is as follows: the liquid working medium volume is determined according to the liquid filling rate of the vapor chamber of the layered composite absorbent core, and the initial effective thickness of each layer of the absorbent core is calculated in descending order of the capillary pressure according to the capillary pressure of the absorbent core, as shown in the following formula: In the formula, h 0i is the initial effective thickness of the wick calculated for the i-th time, h wi is the thickness of the wick calculated for the i-th time, V li To calculate the remaining liquid volume of the i-th wick, V wi is the pore volume of the wick calculated for the i-th time.

5. The prediction method according to claim 1, characterized in that: The step of determining the effective heat conduction thickness of each layer of the wick comprises: (1) The liquid transfer volume in the wick is calculated according to the heating power and liquid level retreat method, as shown in the following formula: Where V t is the volume of the transferred liquid, Q is the heating power, Δt is the buffer time, h fg is the latent heat of phase change, ρ l is the working fluid density; (2) According to the liquid transfer volume, the effective heat transfer thickness of the evaporation end wick is calculated in sequence from the steam chamber to the wall surface, as shown in the following formula: Where V ti To calculate the remaining volume of the transferred liquid at the i-th wick, V 0i To calculate the initial liquid volume inside the i-th wick, h ei is the effective heat transfer thickness of the wick at the evaporation end, A si is the coverage area of ​​the heat transfer region of the i-th wick; (3) According to the liquid transfer volume, the effective heat transfer thickness of the condensation end wick is calculated in sequence from the steam chamber to the wall surface, as shown in the following formula: In the formula, h ci is the effective heat transfer thickness of the ith wick calculated at the condensation end.

6. The prediction method according to claim 1, characterized in that: The series-parallel relationship of the thermal resistance network model of the absorbent core is determined based on: according to the covering relationship between two adjacent layers of the absorbent core, the absorbent core is divided into a covered area and a non-covered area, the thermal resistances of the two adjacent layers of the absorbent core in the covered area are in a series relationship, and the heat conduction path of the absorbent core in the non-covered area is in a parallel relationship with the heat conduction path of the absorbent core in the covered area.

7. The prediction method according to claim 1, characterized in that: When calculating the thermal conduction resistance of the evaporation end wall and the evaporation phase change resistance, the heat transfer area is the area corresponding to the heat source.

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