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

Abstract

The invention discloses a numerical calculation method for capillary limit heat transfer characteristics of a composite wick structure heat pipe. The method comprises the following steps: determining an initial heat pipe working environment and wick structure parameters; constructing a liquid phase flow model based on the working environment of the heat pipe, the structural parameters of the wick, the initialized flow field and the temperature field, and solving to obtain the liquid phase flow velocity and the liquid phase pressure distribution; establishing a heat pipe condensation section heat transfer equation based on the liquid phase flow velocity and the liquid phase pressure distribution, and solving to obtain the steam temperature; building a steam flow model based on the steam temperature, solving the steam flow model, and correcting an output result of the liquid phase flow model and the steam temperature based on a solving result; a heat pipe evaporation section heat transfer equation is constructed based on the output result of the corrected liquid phase flow model and the steam temperature, and evaporation section wall surface temperature distribution is solved; and performing iterative calculation on each heat transfer process parameter based on the initial heat pipe working environment, the wick structure parameter, the initialized flow field and the temperature field to obtain the capillary limit heat transfer characteristic 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 the advantages of 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 is carried out 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 the capillary radius, porosity, permeability and other parameters 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 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 liquid wick structure, comprising:

[0005] 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, initial flow field and temperature field, and solve to obtain the liquid phase flow velocity and liquid phase pressure distribution;

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

[0007] Building 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] Based on the output result of the modified liquid phase flow model and the steam temperature, a heat transfer equation for the evaporation section of the heat pipe is constructed, and the heat transfer equation for the evaporation section of the heat pipe is solved to obtain the temperature distribution of the evaporation section wall surface;

[0009] Based on the initial heat pipe working environment, the liquid wick structure parameters, the initial flow field and temperature field, the condensed 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 are discretely iterated and calculated until convergence to obtain the capillary limit heat transfer characteristics of the heat pipe.

[0010] Optionally, the expression of the liquid phase flow model is:

[0011]

[0012]

[0013] Wherein, μ represents the kinematic viscosity of the liquid medium; u1 represents the flow velocity of the liquid inside the first layer of wire mesh; u2 represents the flow velocity of the liquid 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 medium; g represents the acceleration of gravity; P1 represents the pressure of the liquid inside the first layer of wire mesh; P2 represents the pressure of the liquid 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.

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

[0015]

[0016] Q c =q c ·A c

[0017] In the formula, ρ l Indicates the density of liquid working fluid; 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 Indicates the heat flux density of the heat pipe condensation section; A c Represents the area of ​​the condensation section.

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

[0019] The expression for calculating the heat transfer coefficient of the condensation section and the steam temperature of the condensation section is:

[0020]

[0021]

[0022] In the formula, 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] In the formula, 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 liquid working fluid; f represents the friction coefficient between steam and liquid; Po represents the Poiseuille number; Re represents the Reynolds number; 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] Among them, the expression for calculating the heat transfer coefficient of the evaporation section and the steam temperature of the evaporation section is:

[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; Indicates the evaporation adjustment 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 calculation 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, determine 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, calculating the local average flow velocity based on the liquid phase flow velocity and updating the condensation volume flow rate;

[0041] S6, execute S3-S5 cyclically until the relative error meets the allowable error, and then enter S7;

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

[0043] S8, determining the initial condensation section steam temperature;

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

[0045] S10, execute S8-S9 cyclically until the relative error meets the allowable error, and then enter S11;

[0046] S11, calculating the steam velocity and gas-liquid shear force based on the steam flow model, and when the relative error meets the allowable error, entering S12, otherwise repeating S3-S11;

[0047] S12, calculating the wall temperature of the evaporation section based on the heat transfer equation of the evaporation section of the heat pipe, and ending the calculation when the relative error meets the allowable error, otherwise repeating 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 phase working fluid in the capillary core; the algorithm structure is simple and has good convergence; through heat transfer analysis, the internal flow heat transfer model of the heat pipe is reasonably simplified under the premise of ensuring the calculation speed and accuracy of the model; it can output clear flow field and temperature field result diagrams, providing ideas and data references for the design of composite liquid wick structure heat pipes; the present invention is suitable for various types of composite liquid wick structures, including wire mesh superposition structures with different mesh sizes or wire mesh covering groove structures, and has wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

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

[0054] Figure 2 The present invention is a flowchart 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 in the embodiments of the present 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] Embodiment 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 liquid wick structure, comprising the following steps:

[0059] Determine the initial working environment of the heat pipe and the structural parameters of the wick; construct a liquid phase flow model based on the working environment of the heat pipe, the structural parameters of the wick, the initial flow field and the temperature field, and solve it to obtain the liquid phase flow velocity and the liquid phase pressure distribution; establish the heat transfer equation of the condensation section of the heat pipe based on the liquid phase flow velocity and the liquid phase pressure distribution, and solve the heat transfer equation of the condensation section of the heat pipe 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 evaporation section of the heat pipe based on the output result of the corrected liquid phase flow model and the steam temperature, and solve the heat transfer equation of the evaporation section of the heat pipe to obtain the wall temperature distribution of the evaporation section; based on the initial working environment of the heat pipe, the structural parameters of the wick, the initial flow field and the 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 , Length of insulation section L a , evaporation section length L e , the porosity of the first screen (or groove) ε1, the porosity of the second screen ε2, the permeability of the first screen (or groove) κ1, the permeability of the second screen κ2, the effective capillary pore size of the first screen (or groove) r c,1 、The effective capillary pore size of the second layer of screen r c,2 , type and properties of working fluid, type and 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 that according to the Brinkman equation, the liquid phase flow equation in the two-layer structure of the composite liquid absorbent core can be expressed as:

[0062]

[0063]

[0064]

[0065] Where: μ represents the kinematic viscosity of the liquid phase working fluid / (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 fluid / (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, C4 represent the unknown 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 velocity and velocity gradient at the junction 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] In the formula, u x represents the component of the liquid velocity in the wick in the x direction / (m·s -1 );u y represents 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 (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 liquid 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 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 unknown coefficients of the general solution of equation (5) which are solved by boundary conditions (6). 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 liquid absorbent core can be expressed as equation (8).

[0076] The solution process of the liquid phase flow rate in the liquid core 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 absorbent core / (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 liquid 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 liquid wick in the (i-1)th calculation unit / (m·s -1 );L c Indicates the length of the condensation section / (m); n c Represents the total number of calculation units in the condensation section / (-).

[0080] The local liquid phase velocity of the calculation unit is calculated by equation (1); the condensation volume flow rate of the adjacent calculation unit is solved by equation (11). The program calculates the flow field along the positive direction of the x-axis according to the discretized step size. The solution of the evaporation section flow field is basically the same as the calculation process of the condensation section.

[0081] Step 3: Modeling and solving 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, and the calculation formula is:

[0082] q c =ρ1·V cond ·h fg (12)

[0083] Q c =q c ·A c (13)

[0084] In the formula, ρ l Indicates the density of liquid working fluid / (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 absorbent core / (m 3 ·s -1 );Q c Indicates 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 structure with different structures in the liquid-filled state is:

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

[0087]

[0088] In the formula, k eff,1 The effective thermal conductivity of the groove structure filled with liquid / (W·m -1 ·K -1 );k eff,2 The effective thermal conductivity of the sintered multilayer metal mesh structure filled with liquid / (W·m -1 ·K -1 );k l Indicates the thermal conductivity of the liquid medium in the wick / (W·m -1 ·K -1 );k s It represents 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] In the formula, 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 the 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 specific 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 and steam temperature of the condensation section are:

[0094]

[0095]

[0096] In the formula, 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 It represents the effective thermal conductivity of the first layer of the composite absorbent core / (W·m -1 ·K -1 );k eff,2 It 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] In the formula, 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 fluid / (kg·m -3 );ρ l Indicates the density of liquid working fluid / (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 wall temperature of the evaporation section 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 the 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 specific 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, the liquid flow rate in the wire mesh core is solved by formula (1), the local average velocity is calculated, and the new condensation volume flow rate Vcond is calculated. 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) The steam flow rate is calculated according to formula (20), and the steam flow shear stress τ is calculated according to formula (21) v If the relative error meets the tolerance requirement, 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: Calculation is completed, and the velocity, pressure and temperature distribution, as well as the capillary limiting power of the heat pipe are output.

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

Claims

1. A numerical calculation method for the capillary limit heat transfer characteristics of a composite liquid 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 initial 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 a heat pipe condensation section based on the liquid phase flow velocity and the liquid phase pressure distribution, and solving the heat transfer equation for the heat pipe condensation section to obtain the steam temperature; Building 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; Based on the output result of the modified liquid phase flow model and the steam temperature, a heat transfer equation for the evaporation section of the heat pipe is constructed, and the heat transfer equation for the evaporation section of the heat pipe is solved to obtain the temperature distribution of the evaporation section wall surface; 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 of the capillary limit heat transfer characteristics of the composite liquid wick structure heat pipe according to claim 1 is characterized in that: The expression of the liquid phase flow model is: Wherein, μ represents the kinematic viscosity of the liquid medium; u1 represents the flow velocity of the liquid inside the first layer of wire mesh; u2 represents the flow velocity of the liquid 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 medium; g represents the acceleration of gravity; P1 represents the pressure of the liquid inside the first layer of wire mesh; P2 represents the pressure of the liquid 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 of the capillary limit heat transfer characteristics of the composite liquid wick structure heat pipe according to claim 1, characterized in that: The heat transfer equation of the heat pipe condensation section is expressed as: q c =ρ1·V cond ·h fg Q c =q c ·A c In the formula, ρ l Indicates the density of liquid working fluid; 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 Indicates the heat flux density of the heat pipe condensation section; A c Indicates the area of ​​the condensation section.

4. The numerical calculation method of the capillary limit heat transfer characteristics of the composite liquid wick structure heat pipe according to claim 3 is characterized in that: The process of solving the heat transfer equation of the heat pipe condensation section also includes calculating the heat transfer coefficient of the condensation section and the steam temperature of the condensation section; The expression for calculating the heat transfer coefficient of the condensation section and the steam temperature of the condensation section is: In the formula, 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 of the capillary limit heat transfer characteristics of the composite liquid wick structure heat pipe according to claim 1, characterized in that: The expression of the steam flow model is: <h2 style=";text-align:left;direction:ltr">Po = fRe = 96(1 - 1.3553z + 1.9467z<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> -1.7012z<h2 style=";text-align:left;direction:ltr"> 3 <h2 style=";text-align:left;direction:ltr"> +0.9564z<h2 style=";text-align:left;direction:ltr"> 4 <h2 style=";text-align:left;direction:ltr"> -0.2537z<h2 style=";text-align:left;direction:ltr"> 5 <h2 style=";text-align:left;direction:ltr"> ) In the formula, 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 liquid working fluid; f represents the friction coefficient between steam and liquid; Po represents the Poiseuille number; Re represents the Reynolds number; z represents the aspect ratio.

6. The numerical calculation method of the capillary limit heat transfer characteristics of the composite liquid 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; Among them, the expression for calculating the heat transfer coefficient of the evaporation section and the steam temperature of the evaporation section is: 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; Indicates the evaporation adjustment 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 liquid wick structure heat pipe according to claim 1, characterized in that: The process of discrete iterative calculation of the condensed 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 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, determine 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, calculating the local average flow velocity based on the liquid phase flow velocity and updating the condensation volume flow rate; S6, execute S3-S5 cyclically until the relative error meets the allowable error, and then enter S7; S7, calculate the flow resistance in two different types of cores. If the resistance is the same, go to S8, otherwise go to S1 and redistribute the flow ratio until convergence; S8, determining the initial condensation section steam temperature; S9, solving the heat transfer coefficient of the condensation section based on the initial steam temperature and the heat transfer equation of the heat pipe condensation section and updating the steam temperature of the condensation section; S10, execute S8-S9 cyclically until the relative error meets the allowable error, and then enter S11; S11, calculating the steam velocity and gas-liquid shear force based on the steam flow model, and when the relative error meets the allowable error, entering S12, otherwise repeating S3-S11; S12, calculating the wall temperature of the evaporation section based on the heat transfer equation of the evaporation section of the heat pipe, and ending the calculation when the relative error meets the allowable error, otherwise repeating S3-S12.

8. The numerical calculation method for the capillary limit heat transfer characteristics of a composite liquid 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.

Images