Numerical calculation method for capillary limit heat transfer characteristics of heat pipe with composite wick structure

Abstract

The present invention discloses a numerical calculation method for the capillary limit heat transfer characteristics of a heat pipe with a composite liquid wick structure. The method comprises the following steps: determining an initial heat pipe working environment and liquid wick structural parameters; constructing a liquid phase flow model based on the heat pipe working environment, the liquid wick structural parameters, an initialized flow field, and a temperature field, and solving the model to obtain a liquid phase flow velocity and a liquid phase pressure distribution; establishing a heat transfer equation for a condensation section of the heat pipe based on the liquid phase flow velocity and the liquid phase pressure distribution, and solving the equation to obtain a steam temperature; constructing a steam flow model based on the steam temperature, solving the equation, and correcting an output result of the liquid phase flow model and the steam temperature based on the solution result; constructing a heat transfer equation for an evaporation section of the heat pipe based on the output result of the corrected liquid phase flow model and the steam temperature, and solving the equation to obtain a wall temperature distribution of the evaporation section; and iteratively calculating each heat transfer process parameter based on the initial heat pipe working environment, the liquid wick structural parameters, the initialized flow field, and the temperature field, and obtaining the capillary limit heat transfer characteristics of the heat pipe.

Description

Technical Field

[0001] The invention belongs to the technical field of phase change heat transfer equipment, and in particular relates to a numerical calculation method for the capillary limit heat transfer characteristics of a heat pipe with a composite liquid wick structure. Background Art

[0002] As a heat transfer device with advantages such as high reliability, high operating temperature and high heat flux density, heat pipes are widely used in fields with high heat dissipation requirements, such as electronics, chemical industry, aerospace, and reactors. When the heat pipe is working normally, a steady-state gas-liquid two-phase circulation flow occurs inside it. When the input power exceeds a certain critical value, the maximum suction force provided by the wick cannot meet the liquid phase reflux requirements, resulting in local drying of the evaporation section and failure of the heat pipe, that is, reaching the capillary limit power of the heat pipe. The capillary limit is closely related to parameters such as the capillary radius, porosity, and permeability of the wick. Among them, the upper layer of the composite wick is a porous structure with high suction performance, and the lower layer is a low flow resistance structure, which can effectively improve the heat transfer performance of the heat pipe. The operation of the heat pipe involves multiple physical processes, the interaction of two-phase flow, and the complex coupling of phase change process and flow heat transfer and mass transfer process, which makes it difficult to study the heat transfer enhancement mechanism of the heat pipe. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention proposes a numerical calculation method for the capillary limit heat transfer characteristics of a heat pipe with a composite liquid wick structure to solve the problems existing in the above-mentioned prior art.

[0004] To achieve the above object, the present invention provides a numerical calculation method for the capillary limit heat transfer characteristics of a heat pipe with a composite wick structure, comprising:

[0005] Determining the initial heat pipe working environment and liquid wick structural parameters; constructing a liquid phase flow model based on the heat pipe working environment, liquid wick structural parameters, initialized flow field and temperature field, and solving to obtain the liquid phase flow velocity and liquid phase pressure distribution;

[0006] Establishing a heat transfer equation for the condensation section of the heat pipe based on the liquid phase flow velocity and the liquid phase pressure distribution, and solving the heat transfer equation for the condensation section of the heat pipe to obtain the steam temperature;

[0007] constructing a steam flow model based on the steam temperature, solving the steam flow model to obtain a new value of gas-liquid shear force, and correcting an output result of a liquid phase flow model and the steam temperature based on the new value of gas-liquid shear force;

[0008] constructing a heat transfer equation for the evaporation section of the heat pipe based on the output result of the modified liquid phase flow model and the steam temperature, and solving the heat transfer equation for the evaporation section of the heat pipe to obtain the temperature distribution on the wall surface of the evaporation section;

[0009] Based on the initial heat pipe working environment, wick structure parameters, initial flow field and temperature field, discrete iterative calculations are performed on the condensed liquid phase volume flow rate, flow distribution ratio of each layer, steam temperature, gas-liquid shear force, and evaporation section temperature until convergence to obtain the capillary limit heat transfer characteristics of the heat pipe.

[0010] Optionally, the liquid phase flow model is expressed as:

[0011]

[0012]

[0013] Wherein, μ represents the kinematic viscosity of the liquid phase; u1 represents the liquid phase flow velocity inside the first layer of wire mesh; u2 represents the liquid phase flow velocity inside the second layer of wire mesh; ε1 represents the porosity of the first layer of wire mesh; ε2 represents the porosity of the second layer of wire mesh; κ1 represents the permeability of the first layer of wire mesh; κ2 represents the permeability of the second layer of wire mesh; ρ represents the density of the liquid phase; g represents the acceleration of gravity; P1 represents the liquid phase pressure inside the first layer of wire mesh; P2 represents the liquid phase pressure inside the second layer of wire mesh; u x represents the component of the liquid flow velocity in the wick in the x direction; u y represents the component of the liquid flow velocity in the wick in the y direction; x represents the axial coordinate of the heat pipe; y represents the radial coordinate of the heat pipe.

[0014] Optionally, the heat transfer equation of the heat pipe condensation section is expressed as:

[0015]

[0016] Q c =q c ·A c

[0017] Where, ρ l Indicates the density of liquid working medium; h fg Indicates the latent heat of vaporization phase change; V cond represents the total condensation volume flux in the composite wick; Q c represents the heat transfer rate of the heat pipe; q c A represents the heat flux density of the heat pipe condensation section; c Indicates the area of ​​the condensation section.

[0018] Optionally, the process of solving the heat transfer equation of the condensation section of the heat pipe further includes calculating the heat transfer coefficient of the condensation section and the steam temperature of the condensation section;

[0019] The expressions for calculating the heat transfer coefficient of the condensation section and the steam temperature of the condensation section are as follows:

[0020]

[0021]

[0022] Where h c,sum represents the total heat transfer coefficient of the condensation section; h c,i represents the condensation heat transfer coefficient of the i-th calculation unit; δ1 represents the thickness of the first layer of the composite absorbent core; δ2 represents the thickness of the second layer of the composite absorbent core; k eff,1 represents the effective thermal conductivity of the first layer of the composite absorbent core; k eff,2 represents the effective thermal conductivity of the second layer of the composite absorbent core; T v Indicates steam temperature; T c Represents the wall temperature of the condensation section.

[0023] Optionally, the steam flow model is expressed as:

[0024]

[0025]

[0026] Po=fRe=96(1-1.3553z+1.9467z 2 -1.7012z 3 +0.9564z 4 -0.2537z 5 )

[0027]

[0028] Where u v Indicates steam velocity; V cond represents the total condensation volume flux in the composite wick; τ v represents the gas-liquid shear force; ρ v represents the density of gas phase working fluid; ρ l represents the density of the liquid working medium; f represents the friction resistance coefficient between steam and liquid; Po represents the Poiseuille number; Re represents the Reynolds number; and z represents the aspect ratio.

[0029] Optionally, the process of solving the heat transfer equation of the evaporation section of the heat pipe further includes calculating the heat transfer coefficient of the evaporation section and the steam temperature of the evaporation section;

[0030] The expressions for calculating the heat transfer coefficient and steam temperature of the evaporation section are:

[0031]

[0032]

[0033]

[0034] Where, P v Indicates steam pressure; Tv represents the steam temperature; R represents the universal gas constant; M represents the molecular weight of the steam; h e,sum Indicates the total heat transfer coefficient of the evaporation section; h e,i represents the evaporation heat transfer coefficient of the i-th calculation unit; δ1 represents the thickness of the first layer of the composite absorbent core; δ2 represents the thickness of the second layer of the composite absorbent core; v lv It represents the difference in specific volume between vapor and liquid; represents the evaporation regulation coefficient; h lv Indicates the latent heat of vaporization; k eff,1 k represents the effective thermal conductivity of the first layer of the wick; eff,2 represents the effective thermal conductivity of the second layer of the wick; T v Indicates steam temperature; T e represents the wall temperature of the evaporation section; q e Represents the heat flux density of the evaporation section.

[0035] Optionally, the process of performing discrete iterative calculations on the structural parameters, phase flow velocity and liquid phase pressure distribution, condensation section heat transfer power, condensation section heat flux density, steam velocity, steam pressure distribution, evaporation section heat transfer power and evaporation section heat flux density includes:

[0036] S1. Input heat pipe parameters, capillary wick parameters and condensation section wall temperature;

[0037] S2, initialize the traffic distribution ratio between the two layers;

[0038] S3, determining the initial condensation volume flow rate, the initial evaporation section wall temperature, and the initial gas-liquid shear force;

[0039] S4, calculating the liquid phase flow velocity based on the initial condensation volume flow rate, the initial evaporation section wall temperature, the initial gas-liquid shear force and the liquid phase flow model;

[0040] S5. Calculate the local average flow velocity based on the liquid phase flow velocity and update the condensation volume flow rate;

[0041] S6, loop through S3-S5 until the relative error meets the allowable error, and then go to S7;

[0042] S7: Calculate the flow resistance in two different types of cores. If the resistance is the same, proceed to S8; otherwise, proceed to S1 to redistribute the flow ratio until convergence.

[0043] S8. Determine the steam temperature in the initial condensing section;

[0044] S9, solving the condensation section heat transfer coefficient based on the initial steam temperature and the heat transfer equation of the heat pipe condensation section and updating the condensation section steam temperature;

[0045] S10, loop through S8-S9 until the relative error meets the allowable error, and then proceed to S11;

[0046] S11. Calculate steam velocity and gas-liquid shear force based on the steam flow model. If the relative error meets the allowable error, proceed to S12. Otherwise, repeat S3-S11.

[0047] S12. Calculate the evaporation section wall temperature based on the heat transfer equation of the heat pipe evaporation section. When the relative error meets the allowable error, terminate the calculation. Otherwise, repeat S3-S12.

[0048] Optionally, the convergence condition of the discrete iterative calculation is: the relative error of the evaporation section wall temperature meets the tolerance requirement;

[0049] The tolerance requirement is: |1-F * / F|≤10 -3 , where F * and F are the new and old values ​​respectively.

[0050] Compared with the prior art, the present invention has the following advantages and technical effects:

[0051] The present invention can calculate the pressure distribution, velocity distribution and wall temperature distribution of the liquid working fluid in the capillary wick; the algorithm structure is simple and has good convergence; through heat transfer analysis, the internal flow and heat transfer model of the heat pipe is reasonably simplified while ensuring the calculation speed and accuracy of the model; it can output clear and concise flow field and temperature field result diagrams, providing ideas and data references for the design of heat pipes with composite liquid wick structures; the present invention is applicable to various types of composite liquid wick structures, including structures with superimposed screens of different mesh sizes or structures with screens covering grooves, and has wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0053] Figure 1 A schematic diagram of a system according to an embodiment of the present invention;

[0054] Figure 2 This is a flow chart of a numerical calculation method for the capillary limit heat transfer characteristics of a heat pipe with a composite liquid wick structure according to an embodiment of the present invention. DETAILED DESCRIPTION

[0055] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0056] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0057] Example 1

[0058] like Figure 1-Figure 2 As shown, this embodiment provides a numerical calculation method for the capillary limit heat transfer characteristics of a heat pipe with a composite wick structure, comprising the following steps:

[0059] Determine the initial heat pipe working environment and liquid wick structural parameters; construct a liquid phase flow model based on the heat pipe working environment, liquid wick structural parameters, initialized flow field and temperature field, and solve to obtain the liquid phase flow velocity and liquid phase pressure distribution; establish the heat transfer equation of the heat pipe condensation section based on the liquid phase flow velocity and liquid phase pressure distribution, and solve the heat transfer equation of the heat pipe condensation section to obtain the steam temperature; construct a steam flow model based on the steam temperature, solve the steam flow model to obtain a new value of the gas-liquid shear force, and correct the output result of the liquid phase flow model and the steam temperature based on the new value of the gas-liquid shear force; construct the heat transfer equation of the heat pipe evaporation section based on the output result of the corrected liquid phase flow model and the steam temperature, and solve the heat transfer equation of the heat pipe evaporation section to obtain the evaporation section wall temperature distribution; based on the initial heat pipe working environment, liquid wick structural parameters, initialized flow field and temperature field, perform discrete iterative calculations on the condensing liquid phase volume flow rate, the flow distribution ratio of each layer, the steam temperature, the gas-liquid shear force, and the evaporation section temperature until convergence to obtain the capillary limit heat transfer characteristics of the heat pipe.

[0060] Step 1: Determine the working environment and structural parameters of the heat pipe, including the condensation section temperature T c , condensation section length L c , insulation section length L a , evaporation section length L e , the porosity of the first layer of wire mesh (or groove) ε1, the porosity of the second layer of wire mesh ε2, the permeability of the first layer of wire mesh (or groove) κ1, the permeability of the second layer of wire mesh κ2, the effective capillary pore size of the first layer of wire mesh (or groove) r c,1 , effective capillary pore size r of the second layer of screen c,2 , type and physical properties of working fluid, type and physical properties of wire mesh (or groove) material;

[0061] Step 2: Establishment and numerical solution of the liquid phase flow model inside the porous medium of the high-temperature heat pipe. The specific process is as follows: According to the Brinkman equation, the liquid phase flow equation in the two-layer structure of the composite liquid wick can be expressed as:

[0062]

[0063]

[0064]

[0065] Where: μ represents the kinematic viscosity of the liquid working medium / (N·s·m -2 ); x represents the axial coordinate of the heat pipe / (m); y represents the radial coordinate of the heat pipe / (m); u1 represents the liquid flow velocity inside the first layer of wire mesh (or groove) / (m·s -1 ); u2 represents the liquid flow velocity inside the second layer of screen / (m·s -1 ); ε1 represents the porosity of the first layer of wire mesh (or groove) / (-); ε2 represents the porosity of the second layer of wire mesh / (-); κ1 represents the permeability of the first layer of wire mesh (or groove) / (m 2 ); κ2 represents the permeability of the second layer of wire mesh / (m 2 ); ρ represents the density of liquid working medium / (kg·m -3 ); g represents the acceleration due to gravity / (m·s -2 ); P1 represents the liquid pressure inside the first layer of screen (or groove) / (Pa); P2 represents the liquid pressure inside the second layer of screen / (Pa); δ1 represents the thickness of the first layer of screen (or groove) / (m); δ2 represents the thickness of the second layer of screen / (m); C1, C2, C3, and C4 represent the undetermined coefficients of the general solution of equation (1), which are solved by boundary conditions (3). The flow boundary condition is the no-slip condition between the bottom wick and the wall (y = 0), and the liquid phase velocity and velocity gradient at the intersection of the two layers of the composite structure are the same (y = δ1). The shear stress at the gas-liquid interface is equal to the gas phase flow shear stress (y = δ1 + δ2).

[0066] The continuity equation for liquid flow is:

[0067]

[0068] Where u x The component of the liquid velocity in the wick in the x direction (m·s -1 );u y The component of the liquid velocity in the wick in the y direction (m·s -1 ); x represents the axial coordinate of the heat pipe / (m); y represents the radial coordinate of the heat pipe / (m).

[0069] Taking the condensation process as an example, assuming that the velocity in the y direction corresponds to the condensation liquid phase volume flow rate V cond The solution process of liquid phase pressure is:

[0070]

[0071]

[0072]

[0073]

[0074]

[0075] Where μ represents the kinematic viscosity of the liquid phase working medium / (N·s·m -2 ); x represents the axial coordinate of the heat pipe / (m); y represents the radial coordinate of the heat pipe / (m); u1 represents the liquid flow velocity inside the first layer of the composite liquid wick / (m·s -1 ); u2 represents the liquid flow velocity inside the second layer of the composite absorbent core / (m·s -1 ); ε1 represents the porosity of the first layer of the composite absorbent core / (-); ε2 represents the porosity of the second layer of the composite absorbent core / (-); κ1 represents the permeability of the first layer of the composite absorbent core / (m 2 ); κ2 represents the permeability of the second layer of the composite absorbent core / (m 2 ); P1 represents the internal liquid phase pressure of the first layer of the composite absorbent core / (Pa); P2 represents the internal liquid phase pressure of the second layer of the composite absorbent core / (Pa); δ1 represents the thickness of the first layer of the composite absorbent core / (m); δ2 represents the thickness of the second layer of the composite absorbent core / (m); r c,2 represents the effective capillary radius of the second layer of screen wick / (m); γ represents the surface tension coefficient of the phase working medium / (N·m -1 ); L represents the heat pipe length / (m); V cond,1 represents the condensation volume flux of the first layer of the composite absorbent core / (m 3 ·s -1 );V cond,2 represents the condensation volume flux of the second layer of the composite absorbent core / (m 3 ·s -1 ); A1 and A2 represent the undetermined coefficients of the general solution of Equation (5), which are solved using boundary conditions (6). The capillary pressure is the Laplace pressure at the inlet of the condensation section and the outlet of the evaporation section. The liquid phase pressure gradient in the two-layer structure of the composite wick can be expressed as Equation (8).

[0076] The solution process of the liquid phase flow rate in the wick is:

[0077] V cond =V cond,1 +V cond,2 (10)

[0078]

[0079] Where V cond represents the total condensation volume flux in the composite wick / (m 3 ·s -1 );Vcond,1 represents the condensation volume flux of the first layer of the composite absorbent core / (m 3 ·s -1 );V cond,2 represents the condensation volume flux of the second layer of the composite absorbent core / (m 3 ·s -1 ); δ1 represents the thickness of the first layer of the composite absorbent core / (m); δ2 represents the thickness of the second layer of the composite absorbent core / (m); represents the average flow rate of the liquid phase in the upper and lower layers of the wick in the i-th calculation unit / (m·s -1 ); represents the average flow rate of the liquid phase in the upper and lower layers of the wick in the (i-1)th calculation unit / (m·s -1 );L c Indicates the length of the condensation section / (m); n c Indicates the total number of calculation units in the condensation section / (-).

[0080] The local liquid velocity of a computational cell is calculated using Equation (1), and the condensation volume flow rate of adjacent computational cells is solved using Equation (11). The program calculates the flow field along the positive x-axis, following the discretized step size. The flow field solution for the evaporation section is essentially the same as the calculation process for the condensation section.

[0081] Step 3: Model and solve the heat transfer process of the heat pipe condensation section. The specific heat transfer process mainly includes the phase change process and the heat conduction process of the liquid-filled wick. The heat transfer power of the heat pipe is calculated by the product of the condensation heat transfer flux and the condensation section area. The condensation heat transfer flux can be obtained by the condensation volume flux. The calculation formula is:

[0082] q c =ρ1·V cond ·h fg (12)

[0083] Q c =q c ·A c (13)

[0084] Where, ρ l Indicates the density of liquid working medium / (kg·m -3 );h fg Indicates the latent heat of vaporization phase change / (kJ·kg -1 );V cond represents the total condensation volume flux in the composite wick / (m 3 ·s -1 );Q c represents the heat transfer rate of the heat pipe / (W); q c Indicates the heat flux density of the heat pipe condensation section / (W·m -2 );A cIndicates the area of ​​condensation section / (m 2 ).

[0085] The effective thermal conductivity of the wick structures with different structures in the liquid-filled state is:

[0086] k eff,1 =k l ε1+k s (1-ε1) (14)

[0087]

[0088] Where k eff,1 Indicates the effective thermal conductivity of the liquid-filled groove structure / (W·m -1 ·K -1 );k eff,2 The effective thermal conductivity of the liquid-filled sintered multilayer wire mesh structure is (W·m -1 ·K -1 );k l Indicates the thermal conductivity of the liquid working medium in the wick / (W·m -1 ·K -1 );k s Indicates the thermal conductivity of the solid material of the wick / (W·m -1 ·K -1 ), ε1 represents the groove porosity / (-); ε2 represents the wire mesh porosity / (-).

[0089] The calculation process of the heat transfer coefficient of the condensation process is:

[0090]

[0091]

[0092] Where, ρ v Indicates steam density / (kg·m -3 );P v Indicates steam pressure / (Pa); T v represents the steam temperature / (K); R represents the universal gas constant / (R=8.314J·mol -1 ·K -1 ); M represents the molecular weight of steam / (g·mol -1 );h c,i represents the condensation heat transfer coefficient of the i-th calculation unit / (W·m -2 ·K -1 );v lv Indicates the volume difference between steam and liquid / (kg·m -3 ); Indicates the condensation adjustment coefficient, ranging from 0.02 to 0.04 / (-); h lvIndicates the latent heat of vaporization / (kJ·kg -1 ).

[0093] The total thermal resistance between the condensation wall and the steam is the sum of the thermal conductivity resistance of the liquid-filled composite wire mesh and the phase change heat transfer resistance of the gas-liquid interface. The heat transfer coefficient of the condensation section and the steam temperature are:

[0094]

[0095]

[0096] Where h c,sum represents the total heat transfer coefficient of the condensation section / (W·m -2 ·K -1 );h c,i represents the condensation heat transfer coefficient of the i-th calculation unit / (W·m -2 ·K -1 ); δ1 represents the thickness of the first layer of the composite absorbent core / (m); δ2 represents the thickness of the second layer of the composite absorbent core / (m); k eff,1 Indicates the effective thermal conductivity of the first layer of the composite absorbent core / (W·m -1 ·K -1 );k eff,2 represents the effective thermal conductivity of the second layer of the composite absorbent core / (W·m -1 ·K -1 );T v Indicates steam temperature / (K); T c represents the wall temperature of the condensation section / (K); q c represents the heat flux density of the condensation section / (W·m -2 ).

[0097] Step 4: Modeling and solving the steam flow process. The flow parameter solution method is as follows:

[0098]

[0099]

[0100] Po=fRe=96(1-1.3553z+1.9467z 2 -1.7012z 3 +0.9564z 4 -0.2537z 5 )(twenty two)

[0101]

[0102] Where u v Indicates steam velocity / (m·s -1 );V condrepresents the total condensation volume flux in the composite absorbent core / (m 3 ·s -1 ); τ v Indicates gas-liquid shear force / (N·m -2 );ρ v Indicates the density of gas phase working medium / (kg·m -3 );ρ l Indicates the density of liquid working medium / (kg·m -3 ); f represents the friction resistance coefficient between steam and liquid / (-), formula (22) corresponds to the calculation of the friction resistance coefficient of flat plate flow, and formula (22) corresponds to the calculation of the friction resistance coefficient of circular tube flow; Po represents the Poiseuille number / (-); Re represents the Reynolds number / (-); z represents the aspect ratio / (-).

[0103] Step 5: Modeling and solving the heat transfer process of the evaporation section of the heat pipe. The specific heat transfer process is similar to that of the condensation section, mainly including the phase change process and the heat conduction process of the liquid-filled wick. The total thermal resistance between the evaporation section wall and the steam is the sum of the thermal conductivity resistance of the liquid-filled composite wire mesh and the phase change heat transfer resistance of the gas-liquid interface. The total heat transfer coefficient of the evaporation section and the evaporation section wall temperature are:

[0104]

[0105]

[0106]

[0107] Where, P v Indicates steam pressure / (Pa); T v represents the steam temperature / (K); R represents the universal gas constant / (R=8.314J·mol -1 ·K -1 ); M represents the molecular weight of steam / (g·mol -1 );h e,sum Indicates the total heat transfer coefficient of the evaporation section / (W·m -2 ·K -1 );h e,i represents the evaporation heat transfer coefficient of the i-th calculation unit / (W·m -2 ·K -1 ); δ1 represents the thickness of the first layer of screen (or groove) of the composite absorbent core / (m); δ2 represents the thickness of the second layer of screen of the composite absorbent core / (m); v lv Indicates the volume difference between steam and liquid / (kg·m -3 ); Indicates the evaporation adjustment coefficient, ranging from 0.02 to 0.04 / (-); h lv Indicates the latent heat of vaporization / (kJ·kg -1 );keff,1 Indicates the effective thermal conductivity of the first layer of the wick / (W·m -1 ·K -1 );k eff,2 Indicates the effective thermal conductivity of the second layer of the wick / (W·m -1 ·K -1 );T v Indicates steam temperature / (K); T e represents the wall temperature of the evaporation section / (K); q e Indicates the heat flux density of the evaporation section / (W·m -2 ).

[0108] Step 6: Discretize the computational domain and perform iterative calculations. The specific calculation steps are as follows:

[0109] (1) Input heat pipe parameters, capillary wick parameters and condenser temperature T c ;

[0110] (2) Assume the traffic distribution ratio between the two layers;

[0111] (3) Assuming the condensation volume flow rate V cond * ;

[0112] (4) Solve the local pressure gradient ΔP according to formula (8);

[0113] (5) Assuming the evaporator temperature T e * , and calculate the liquid thermal properties according to the temperature;

[0114] (6) Assume that the shear stress at the liquid-vapor interface is τ v * ;

[0115] (7) According to the boundary conditions, solve the liquid flow rate in the wire mesh core by formula (1), calculate the local average velocity, and calculate the new condensation volume flow rate Vcond. If the relative error meets the allowable error, proceed to the next step; otherwise, repeat steps (3) to (7) until a converged solution is obtained.

[0116] (8) Calculate the flow resistance in the two different types of cores. If the flow resistance is the same, proceed to the next step; otherwise, proceed to step (1) and assume a new distribution ratio until a converged solution is obtained.

[0117] (9) Assume that the steam temperature is T v * , and calculate the thermophysical properties of steam based on the steam temperature;

[0118] (10) The condensation heat transfer coefficient is solved according to formula (17), and the total heat transfer coefficient is solved according to formula (18).

[0119] Calculate the new steam temperature T v If the relative error meets the allowable error, proceed to the next step;

[0120] Otherwise, repeat steps (9) and (10) until a converged solution is obtained;

[0121] (11) Calculate the steam flow rate according to formula (20), and calculate the steam flow shear stress τ according to formula (21) v If the relative error meets the tolerance requirements, proceed to the next step; otherwise, repeat step (6)

[0122] to (11) until a converged solution is obtained;

[0123] (12) Calculate the evaporator temperature T according to formula (26) e If the relative error meets the tolerance requirement, the calculation ends and the result is output; otherwise, steps (5) to (12) are repeated until a converged solution is obtained;

[0124] Convergence condition: The calculation is performed until the tolerance requirement |1-F is met * / F|≤10-3, where F * and F are the new and old values ​​respectively;

[0125] Step 7: The calculation is completed and the velocity, pressure and temperature distribution, as well as the capillary limit power of the heat pipe are output.

[0126] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A numerical calculation method for the capillary limit heat transfer characteristics of a composite wick structure heat pipe, characterized in that: The following steps are involved: Determine the initial heat pipe working environment and wick structure parameters; Based on the working environment of the heat pipe, the structural parameters of the liquid wick, the initialized flow field and the temperature field, a liquid phase flow model is constructed and the liquid phase flow velocity and liquid phase pressure distribution are obtained by solving the model; Establishing a heat transfer equation for the condensation section of the heat pipe based on the liquid phase flow velocity and the liquid phase pressure distribution, and solving the heat transfer equation for the condensation section of the heat pipe to obtain the steam temperature; constructing a steam flow model based on the steam temperature, solving the steam flow model to obtain a new value of gas-liquid shear force, and correcting an output result of a liquid phase flow model and the steam temperature based on the new value of gas-liquid shear force; constructing a heat transfer equation for the evaporation section of the heat pipe based on the output result of the modified liquid phase flow model and the steam temperature, and solving the heat transfer equation for the evaporation section of the heat pipe to obtain the temperature distribution on the wall surface of the evaporation section; Based on the initial heat pipe working environment, wick structure parameters, initialized flow field and temperature field, discrete iterative calculations are performed on the condensed liquid phase volume flow rate, flow distribution ratio of each layer, steam temperature, gas-liquid shear force, and evaporation section temperature until convergence to obtain the capillary limit heat transfer characteristics of the heat pipe.

2. The numerical calculation method for the capillary limit heat transfer characteristics of a composite wick structure heat pipe according to claim 1, characterized in that: The expression of the liquid phase flow model is: Wherein, μ represents the kinematic viscosity of the liquid phase; u1 represents the liquid phase flow velocity inside the first layer of wire mesh; u2 represents the liquid phase flow velocity inside the second layer of wire mesh; ε1 represents the porosity of the first layer of wire mesh; ε2 represents the porosity of the second layer of wire mesh; κ1 represents the permeability of the first layer of wire mesh; κ2 represents the permeability of the second layer of wire mesh; ρ represents the density of the liquid phase; g represents the acceleration of gravity; P1 represents the liquid phase pressure inside the first layer of wire mesh; P2 represents the liquid phase pressure inside the second layer of wire mesh; u x represents the component of the liquid velocity in the wick in the x direction; u y represents the component of the liquid flow velocity in the wick in the y direction; x represents the axial coordinate of the heat pipe; y represents the radial coordinate of the heat pipe.

3. The numerical calculation method for the capillary limit heat transfer characteristics of a composite wick structure heat pipe according to claim 1, characterized in that: The heat transfer equation of the heat pipe condensation section is expressed as: Where, ρ l represents the density of liquid working medium; h fg Indicates the latent heat of vaporization phase change; V cond represents the total condensation volume flux in the composite wick; Q c represents the heat transfer rate of the heat pipe; q c A represents the heat flux density of the heat pipe condensation section; c Indicates the area of ​​the condensation section.

4. The numerical calculation method for the capillary limit heat transfer characteristics of a composite wick structure heat pipe according to claim 3, characterized in that: The process of solving the heat transfer equation of the condensation section of the heat pipe also includes calculating the heat transfer coefficient of the condensation section and the steam temperature of the condensation section; The expressions for calculating the heat transfer coefficient of the condensation section and the steam temperature of the condensation section are as follows: Where h c,sum represents the total heat transfer coefficient of the condensation section; h c,i represents the condensation heat transfer coefficient of the i-th calculation unit; δ1 represents the thickness of the first layer of the composite absorbent core; δ2 represents the thickness of the second layer of the composite absorbent core; k eff,1 represents the effective thermal conductivity of the first layer of the composite absorbent core; k eff,2 represents the effective thermal conductivity of the second layer of the composite absorbent core; T v Indicates steam temperature; T c Represents the wall temperature of the condensation section.

5. The numerical calculation method for the capillary limit heat transfer characteristics of a composite wick structure heat pipe according to claim 1, characterized in that: The expression of the steam flow model is: Where u v Indicates steam velocity; V cond represents the total condensation volume flux in the composite wick; τ v represents the gas-liquid shear force; ρ v represents the density of gas phase working fluid; ρ l represents the density of the liquid working medium; f represents the friction resistance coefficient between steam and liquid; Po represents the Poiseuille number; Re represents the Reynolds number; and z represents the aspect ratio.

6. The numerical calculation method for the capillary limit heat transfer characteristics of a composite wick structure heat pipe according to claim 1, characterized in that: The process of solving the heat transfer equation of the evaporation section of the heat pipe also includes calculating the heat transfer coefficient of the evaporation section and the steam temperature of the evaporation section; The expressions for calculating the heat transfer coefficient of the evaporation section and the steam temperature of the evaporation section are: Where, P v Indicates steam pressure; T v represents the steam temperature; R represents the universal gas constant; M represents the molecular weight of the steam; h e,sum Indicates the total heat transfer coefficient of the evaporation section; h e,i represents the evaporation heat transfer coefficient of the i-th calculation unit; δ1 represents the thickness of the first layer of the composite absorbent core; δ2 represents the thickness of the second layer of the composite absorbent core; v lv It represents the difference in specific volume between vapor and liquid; represents the evaporation regulation coefficient; h lv Indicates the latent heat of vaporization; k eff,1 k represents the effective thermal conductivity of the first layer of the wick; eff,2 represents the effective thermal conductivity of the second layer of the wick; T v Indicates steam temperature; T e represents the wall temperature of the evaporation section; q e Represents the heat flux density of the evaporation section.

7. The numerical calculation method for the capillary limit heat transfer characteristics of a composite wick structure heat pipe according to claim 1, characterized in that: The process of discrete iterative calculation of the condensate phase volume flow rate, flow distribution ratio of each layer, steam temperature, gas-liquid shear force, and evaporation section temperature includes: S1. Input heat pipe parameters, capillary wick parameters and condensation section wall temperature; S2, initialize the traffic distribution ratio between the two layers; S3, determining the initial condensation volume flow rate, the initial evaporation section wall temperature, and the initial gas-liquid shear force; S4, calculating the liquid phase flow velocity based on the initial condensation volume flow rate, the initial evaporation section wall temperature, the initial gas-liquid shear force and the liquid phase flow model; S5. Calculate the local average flow velocity based on the liquid phase flow velocity and update the condensation volume flow rate; S6, loop through S3-S5 until the relative error meets the allowable error, and then go to S7; S7: Calculate the flow resistance in two different types of cores. If the resistance is the same, proceed to S8; otherwise, proceed to S1 to redistribute the flow ratio until convergence. S8. Determine the steam temperature in the initial condensing section; S9, solving the condensation section heat transfer coefficient based on the initial condensation section steam temperature and the heat transfer equation of the heat pipe condensation section and updating the condensation section steam temperature; S10, loop through S8-S9 until the relative error meets the allowable error, and then proceed to S11; S11. Calculate steam velocity and gas-liquid shear force based on the steam flow model. If the relative error meets the allowable error, proceed to S12. Otherwise, repeat S3-S11. S12. Calculate the evaporation section wall temperature based on the heat transfer equation of the heat pipe evaporation section. When the relative error meets the allowable error, terminate the calculation. Otherwise, repeat S3-S12.

8. The numerical calculation method for the capillary limit heat transfer characteristics of a composite wick structure heat pipe according to claim 7, characterized in that: The convergence condition of the discrete iterative calculation is: the relative error of the evaporation section wall temperature meets the tolerance requirement; The tolerance requirement is: |1-F * / F|≤10 -3 , where F * and F are the new and old values ​​respectively.

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