A method for calculating heat transfer of a pulsating heat pipe with interval capillary wick

Abstract

The application discloses a kind of interval capillary core pulsating heat pipe heat transfer calculation method, comprising: constructing the relationship of temperature and pressure of vapor bullet, calculating vapor bullet pressure;Build liquid bullet energy equation, calculate liquid bullet temperature initial value;Build liquid bullet momentum equation of interval capillary core pulsating heat pipe, calculate liquid bullet displacement;Build different pipe section liquid film length calculation formula, calculate different pipe section liquid film length;Obtain the heat transfer of liquid film evaporation and condensation, calculate corresponding vapor bullet mass change amount;Obtain the relationship of vapor bullet mass flow and pressure, calculate and obtain new value of vapor bullet pressure;Build the relationship of temperature and pressure of vapor bullet, obtain new value of vapor bullet temperature;Build liquid bullet energy equation, obtain new value of liquid bullet temperature and carry out comparison iteration;Obtain the sensible heat of liquid bullet transmission and export, calculate the thermal resistance of pulsating heat pipe;The above calculation result is output, and the calculation of heat transfer model is completed.The application provides guidance for the design and development of interval capillary core pulsating heat pipe.

Description

Technical Field

[0001] This invention belongs to the technical field of phase change heat exchange equipment, and particularly relates to a method for calculating heat transfer in a spaced capillary pulsating heat pipe. Background Technology

[0002] With the trend towards miniaturization and compactness of electronic devices, the heat flux density of microelectronic devices is constantly increasing, seriously affecting the performance and lifespan of equipment. Therefore, the demand for high-efficiency heat dissipation materials is constantly increasing. Pulsating heat pipes, as high-efficiency heat dissipation devices, couple two heat transfer methods: phase change heat transfer and sensible heat transfer through oscillation within microchannels. The vapor pressure difference generated by the latent heat transfer between the evaporation and condensation ends drives the liquid bob to oscillate within the channel. This type of heat pipe has high thermal conductivity and is considered one of the most effective methods to address the challenges of high heat flux density. Due to limitations in its working principle, pulsating heat pipes are difficult to start when placed horizontally or against gravity. Adding a capillary wick to the pulsating heat pipe can solve problems such as difficulty in recirculating liquid in the evaporation section due to gravity, easy burning-out of the evaporation section under high heat flux density conditions, and difficulty in starting up, which are common in low-tube-count pulsating heat pipes. In addition, compared to a fully covered capillary wick, a spaced capillary wick can bring a larger unbalanced pressure difference to adjacent pipes, improve the effective driving force, and at the same time reduce the resistance of the capillary wick to the liquid elastic oscillation, significantly improve the effective thermal conductivity of the liquid working fluid, and enhance the heat transfer performance of the pulsating heat pipe.

[0003] The heat and mass transfer coupling characteristics of the wick, condensate film, and liquid blister within a spaced capillary pulsating heat pipe make the heat transfer and working fluid motion complex. Therefore, providing a numerical simulation method for spaced capillary pulsating heat pipes that simultaneously ensures both speed and accuracy is a problem that urgently needs to be solved by those in the field. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a heat transfer calculation method for spaced capillary pulsating heat pipes. This method can obtain the transient heat transfer and flow characteristics of the working fluid inside spaced and fully covered capillary pulsating heat pipes. Numerical simulations are performed on capillary pulsating heat pipes under different operating conditions to calculate the temperature and pressure of the vapor chamber inside the pulsating heat pipe, as well as the oscillation height, liquid film length, temperature distribution, and thermal resistance of the liquid chamber. This provides suggestions and guidance for the design and engineering application of capillary pulsating heat pipes, thereby solving the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides a method for calculating heat transfer in a spaced capillary pulsating heat pipe, comprising the following steps:

[0006] Obtain the heat pipe size and structural parameters and the capillary wick structural parameters, and construct a pulsating heat pipe model;

[0007] In the pulsating heat pipe model, two initial temperature values ​​for the gas bomb are preset, a functional relationship between the gas bomb temperature and pressure is constructed, and an initial pressure value for the gas bomb is calculated based on the functional relationship between the gas bomb temperature and pressure.

[0008] Construct the liquid-bomb energy equation, and calculate the liquid-bomb temperature distribution based on the liquid-bomb energy equation and the corresponding initial and boundary conditions;

[0009] A liquid-elastic momentum equation for a pulsating heat pipe with a spaced capillary wick is constructed. The shear stresses of the smooth pipe section and the capillary wick-covered pipe section are obtained respectively. Based on the liquid-elastic momentum equation for the pulsating heat pipe with a spaced capillary wick, the shear stresses of different pipe sections, and the initial values ​​of the vapor-elastic pressure, the liquid-elastic displacement is calculated.

[0010] Formulas for calculating the liquid film length of smooth tube segments and capillary core covered tube segments are constructed respectively. Based on the formulas for calculating the liquid film length of different tube segments, the corresponding liquid film lengths are obtained.

[0011] Obtain the heat transfer of liquid film evaporation and condensation, and calculate the corresponding change in vapor bomb mass based on the heat transfer of liquid film evaporation and condensation respectively;

[0012] Obtain the relationship between the mass flow rate and pressure of the gas bomb, and calculate the new value of the gas bomb pressure based on the relationship between the mass flow rate and pressure of the gas bomb and the obtained change in the mass of the gas bomb.

[0013] Based on the functional relationship between the temperature and pressure of the gas bomb and the new value of the gas bomb pressure, the new value of the gas bomb temperature is obtained;

[0014] Based on the aforementioned liquid bomb energy equation and the new value of the gas bomb temperature, the new value of the liquid bomb temperature is obtained;

[0015] The new values ​​of the gas bomb temperature are compared with the given initial values ​​of the gas bomb temperature and iterated to obtain the final new values ​​of the gas bomb and liquid bomb temperatures.

[0016] The sensible heat input and output of the liquid bomb is obtained, and the thermal resistance of the pulsating heat pipe is calculated based on the sensible heat.

[0017] Output the liquid bomb temperature, liquid bomb displacement, liquid film length, change in vapor bomb mass, new value of vapor bomb pressure, new value of vapor bomb temperature, and thermal resistance of pulsating heat pipe to complete heat transfer calculations.

[0018] Optionally, the functional relationship between the temperature and pressure of the vapor bomb is as follows:

[0019]

[0020] Among them, T v0 P is the initial temperature of the gas bomb. v0 γ is the initial pressure of the vapor chamber; P is the heat capacity ratio; γ is the initial pressure of the vapor chamber. v1 P v2 T is the pressure of the vapor spring; V1T V2 These are the temperatures of the gas bomb.

[0021] Optionally, the expressions for the liquid explosive energy equation and the corresponding initial and boundary conditions are as follows:

[0022]

[0023] T = T0, t = 0, 0 < x l <L p

[0024] T = T v1 ,x l =0

[0025] T = T v2 ,x l =L p

[0026] Where T1 is the temperature of the liquid explosive; α l d is the thermal diffusivity; A is the cross-sectional area; d is the heat pipe diameter; L p x is the length of the liquid bullet; l h represents the position of the liquid bullet. sen T is the convective heat transfer coefficient. W T represents the wall temperature. V1 T V2 t represents the temperature of the gas bomb; π represents time; and t is a constant.

[0027] Optionally, the expression for the fluid elasticity equation of a pulsating heat pipe with a spaced capillary wick is shown below:

[0028]

[0029] Where, ρ l For liquid density; ΔP b For pressure loss at the bend; L p,wick τ is the length of the liquid elastic element in the capillary core region; p,wick For the shear stress in the capillary core region; L p,smooth τ is the length of the liquid bullet in the smooth region; p,smooth For the shear stress in the smooth region; P v1 P v2 ρ is the pressure of the two air balloons; g is the acceleration due to gravity.

[0030] Optionally, the formula for calculating the liquid film length of the smooth tube section and the capillary core covered tube section is as follows:

[0031] Formula for calculating the length of a thin liquid film in a smooth tube section:

[0032]

[0033] Formula for calculating the length of the thin liquid film in the capillary wick-covered section:

[0034]

[0035] Among them, L c,i L is the length of the liquid film in the condensation section. e,i δ is the length of the liquid film in the evaporation section. smooth δ represents the thickness of the liquid film in the smooth pipe section. wick The thickness of the liquid film in the wick; m v v is the mass of the vapor bomb; u is the velocity of the condensate in the capillary wick in the x-direction; v p ε is the fluid velocity; ρ is the porosity of the wire mesh capillary core; and ρ is the liquid density.

[0036] Optionally, the formula for calculating the heat transfer of liquid film evaporation and condensation is as follows:

[0037]

[0038] Among them, Q cond,i For heat transfer during liquid film condensation; Q evp,i For heat transfer during liquid film evaporation; h sum L is the overall heat transfer coefficient. c,i L is the length of the liquid film in the condensation section. e,i T is the length of the liquid film in the evaporation section. e T c These are the wall temperatures of the evaporation section and the condensation section, respectively.

[0039] Optionally, the formula for calculating the rate of change of mass of the gas bomb is as follows:

[0040]

[0041] Where, m v1 m v2 h is the mass of the gas bomb. fg This is the latent heat of phase transition of the working fluid.

[0042] Optionally, the process of obtaining the relationship between the mass flow rate and pressure of the gas bomb includes: constructing the energy equation and the ideal gas equation of state of the gas bomb; and based on the functional relationship between the energy equation and the ideal gas equation of state of the gas bomb, obtaining the relationship between the mass flow rate and pressure of the gas bomb, as shown below:

[0043]

[0044] Among them, R g P is the gas constant; v1 P v2 These represent the vapor pressure; d is the heat pipe diameter; P v0 γ is the initial pressure of the vapor chamber; L is the heat capacity ratio;e This represents the length of the liquid film in the evaporation section.

[0045] Optionally, the formulas for calculating the sensible heat transferred into and out of the liquid bomb are as follows:

[0046]

[0047] Among them, Q h Sensible heat transferred to the liquid bomb; Q c The sensible heat transferred from the liquid bomb; T l,i h is the temperature of the liquid bomb. sen T is the convective heat transfer coefficient. e T c These are the wall temperatures of the evaporation section and the condensation section, respectively; L p The length of the liquid bullet.

[0048] Optionally, the formula for calculating the thermal resistance of a pulsating heat pipe is as follows:

[0049]

[0050] Where R is the thermal resistance; The average sensible heat transferred to the liquid bomb; The average sensible heat transferred from the liquid bomb; Average condensation heat; This represents the average heat of evaporation. The average sensible heat; This represents the average latent heat.

[0051] Compared with the prior art, the present invention has the following advantages and technical effects:

[0052] (1) The present invention provides a novel method for calculating heat transfer of pulsating heat pipes with spaced capillary wicks, which can calculate and analyze the flow characteristics such as liquid-elastic oscillation displacement, liquid-elastic temperature distribution and liquid film length of pulsating heat pipes with spaced capillary wicks and full capillary wicks, as well as the heat transfer performance such as heat transfer heat and thermal resistance.

[0053] (2) It is applicable to capillary wicks with uniform aperture, capillary wicks with non-uniform aperture, and pulsating heat pipes with spaced and full coverage of various working fluids. Among them, the applicable capillary wick structures include single-structure capillary wicks such as metal powder sintered capillary wicks, woven wire mesh sintered capillary wicks, grooved capillary wicks, and fiber sintered capillary wicks, as well as composite-structure capillary wicks, which have wide applicability.

[0054] (3) A novel algorithm is provided to calculate the liquid film length and thickness based on the presence or absence of capillary wick coverage, and then to calculate the liquid flow condition and heat transfer of the pulsating heat pipe.

[0055] (4) The constructed iterative equations are concise and have good convergence.

[0056] (5) The output can provide a simpler and clearer result diagram, which is convenient for providing design ideas and data references for the design of pulsating heat pipes with intermittent capillary wicks. Attached Figure Description

[0057] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0058] Figure 1 This is a schematic flowchart of the heat transfer calculation method for a spaced capillary pulsating heat pipe according to an embodiment of the present invention.

[0059] Figure 2 This is a schematic diagram of the theoretical model of the spaced capillary pulsating heat pipe according to an embodiment of the present invention. Detailed Implementation

[0060] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0061] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that, in the accompanying drawings... Figure 1 The steps shown in the flowchart can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0062] Example 1

[0063] like Figures 1-2 As shown, this embodiment provides a method for calculating heat transfer in a pulsating heat pipe with intermittently covered capillary wicks, including:

[0064] Step 1: Determine the dimensional and structural parameters of the capillary pulsating heat pipe and establish a pulsating heat pipe model: divide the heat pipe into evaporation, adiabatic, and condensation sections. Select the working fluid properties within the heat pipe and calculate the target parameters for these properties; specify the wall temperatures of the evaporation and condensation sections as T. e T c Given an initial temperature of T for the gas bomb. V1 T V2 .

[0065] The structural parameters include: the diameter and length of the pulsating heat pipe; the thickness, mesh count, material, permeability, and porosity of the capillary wick.

[0066] Step 2: Based on the initial temperature T of the gas bombV1 T V2 The initial value P of the vapor spring pressure is calculated using equations (1) and (2). v1 P v2 ;

[0067]

[0068] Among them, T v0 —Initial temperature of the gas bomb / K; P v0 —Initial pressure of the vapor chamber / Pa; γ —Heat ratio;

[0069] Step 3: Construct the liquid bomb energy equation and calculate the liquid bomb temperature;

[0070] The initial temperature T of the liquid bomb is calculated using the energy equation of the liquid bomb shown in equation (3) and the corresponding initial and boundary conditions equations (4)-(6). l :

[0071]

[0072] In equations (3)-(6): T1—liquid explosive temperature / K; α l — Thermal diffusivity / m 2 ·s -1 A – Cross-sectional area / m 2 d — heat pipe diameter / m; L p —Liquid bullet length / m; x l —Liquid bullet position / m;

[0073] h sen — Convective heat transfer coefficient / W·m -2 ·K -1 ;T W —Wall temperature / K;

[0074] The wall temperature is related to the position of the liquid bomb, and the wall temperature T is determined by equations (7) and (8). W :

[0075]

[0076] In equations (7) and (8): x p —Liquid elastic displacement / m;

[0077] The convective heat transfer coefficient h is calculated using equation (9). sen :

[0078]

[0079] In equation (9): k l — Thermal conductivity of condensate / W·m -1 ·K -1 ;

[0080] Step 4: Construct the corresponding momentum equation for the liquid-elastic fluid based on the arrangement of the capillary cores, and calculate the displacement x of the liquid-elastic fluid. p ;

[0081] The equation for the fluid elasticity of a fully covered capillary pulsating heat pipe is shown in equation (10):

[0082]

[0083] In equation (10): ρ l —Liquid density / kg·m -3 ;ΔP b —Pressure loss at the bend in the pipe / Pa; L p,wick —Length of the liquid explosive in the capillary core region / m; τ p,wick —Shear stress in the capillary core region / Pa;

[0084] The equation for the fluid elasticity of a pulsating heat pipe with a spaced capillary wick is shown in equation (11):

[0085]

[0086] In equation (11): L p,smooth —Length of the liquid bullet in the smooth region / m; τ p,smooth —Shear stress in the smooth region / Pa;

[0087] Pressure loss ΔP at bend b for:

[0088]

[0089] In equation (12): ΔP b —Pressure loss / Pa; ζ —Pressure loss coefficient; ν p — Bulk bullet velocity / m·s -1 Shear stress τ p for:

[0090] τ p =f l ρ l v 2 / 2 (13)

[0091] In equation (13): τ p —Shear stress; f l —Coefficient of friction; v—Condensate flow rate / m·s -1 ;

[0092] Fluid flow friction coefficient f l The coefficient of friction f differs between the capillary wick region and the smooth region, with the coefficient of friction f in the smooth tube being... l for:

[0093]

[0094] Assuming the capillary wick region is a rough tube, the friction coefficient f of the pulsating heat pipe covering the capillary wick can be calculated using the Körbrook-White rough tube equation. l :

[0095]

[0096] In equation (15): e——absolute height of the rough peak, i.e., the thickness of the capillary core / m;

[0097] The displacement x of the liquid elastic force can be calculated based on the above equation. p .

[0098] Step 5: Calculate the liquid film length of the smooth tube section and the capillary core covered tube section according to equations (16) and (17), respectively;

[0099] When the liquid flow passes through a smooth pipe section, a liquid film remains on the wall. The length of the thin liquid film on the smooth pipe section can be calculated using equation (16):

[0100]

[0101] In equation (16): L c,i — Length of liquid film in condensation section / m; L e,i — Evaporation section liquid film length / m; δ smooth — Smooth liquid film thickness / m; m v —Gas bomb mass / kg;

[0102] For pipe sections covered by capillary wicks, the speed at which the liquid film spreads due to capillary force needs to be considered. The length of the liquid film spread on the capillary wick surface can then be calculated using equation (17):

[0103]

[0104] In equation (17): δ wick — Capillary wick liquid film thickness / m; u — Velocity of condensate in the x-direction within the capillary wick / m·s -1 ;v p — Liquid elastic oscillation velocity / m·s -1 ε—Porosity of the wire mesh capillary core;

[0105] Using the Brinkman equation, the velocity distribution equation of the condensate inside the capillary wick is derived:

[0106]

[0107] In equation (18): μ — viscosity of condensate / N·s·m -2P – Local pressure of condensate / Pa; g – Gravitational acceleration / m·s² -2 ;

[0108] Assuming the bottom of the capillary wick, i.e., the point where the capillary wick is in contact with the wall, is a no-slip boundary condition, and the top of the capillary wick, i.e., the point where the capillary wick is in contact with the vapor, is free from shear force, then the local velocity distribution of the condensate can be calculated using the boundary conditions shown in equation (19):

[0109]

[0110] The structural parameters of the capillary core are calculated using equations (20)-(21):

[0111] The porosity ε of the wire mesh capillary core is:

[0112]

[0113] In formula (20): N—mesh count of the wire mesh; d wick —Wire diameter of the capillary core of the wire mesh / mm;

[0114] The permeability κ of the wire mesh capillary core is:

[0115]

[0116] In equation (21): κ——permeability / m 2 ;

[0117] If the pressure gradient of the condensate is the Laplace pressure at the inlet of the liquid condensation section and the outlet of the evaporation section, then the capillary pressure P cap for:

[0118]

[0119] In equation (22): γ—surface tension of the condensate / N·m -1 θ—Contact angle between condensate and capillary wick (°); r e —Effective capillary radius of the evaporation section capillary wick / m;

[0120] For a wire mesh capillary core, the effective radius r of the capillary core e for:

[0121]

[0122] In formula (23): w——pore size of the wire mesh capillary core / m;

[0123] Pressure gradient driving fluid motion within the capillary wick for:

[0124]

[0125] In equation (24): L wick —Length of capillary wick / m;

[0126] Smooth pipe section liquid film thickness δ smooth Calculated using the Aussillous model formula:

[0127]

[0128] In equation (25): r—heat pipe radius / m; Ca—capillary coefficient;

[0129] Capillary core covered section liquid film thickness δ wick Capillary wick thickness;

[0130] Step 6: Calculate the latent heat of vaporization and latent heat of condensation according to equation (26), and calculate the change in vapor bomb mass caused by evaporation and condensation through the latent heat;

[0131] Heat transfer from liquid film evaporation and condensation:

[0132]

[0133] In equation (26): Q cond,i —Liquid film condensation heat transfer / W; Q evp,i —Liquid film evaporation heat transfer / W; h sum —Overall heat transfer coefficient / W·m -2 ·K -1 ;

[0134] For a capillary-covered tube section, the thermal resistance between the steam and the heat pipe condensation wall is mainly composed of the thermal resistance of the capillary and the thermal resistance of the condensation at the gas-liquid interface. Therefore, the overall heat transfer coefficient h... sum for:

[0135]

[0136] The condensation heat transfer coefficient h of the interface i for:

[0137]

[0138] In equation (28): V lv —Specific volume difference between steam and liquid; —The range is 0.02-0.04, here we take 0.03; M —molecular molar mass / kg·kmol -1 ;

[0139] effective thermal conductivity of capillary wick k eff for:

[0140]

[0141] In equation (29): k eff —Effective thermal conductivity of capillary wick / W·m -1 ·K -1 ;k l — Thermal conductivity of liquids / W·m -1 ·K -1 ;k s — Thermal conductivity of capillary wick material / W·m -1 ·K -1 The rate of change of vapor bomb mass due to evaporation and condensation is calculated using equations (30) and (31):

[0142]

[0143] In equations (30) and (31): m v1、 m v2 —Gas bomb mass / kg; h fg —Latent heat of phase transition of working fluid

[0144] / J·kg -1 ;

[0145] Step 7: Based on the first law of thermodynamics, construct the energy equation and ideal gas law of the gas bomb, and calculate the new value of the gas bomb pressure.

[0146] The energy equations for the gas bomb are shown in equations (32) and (33):

[0147]

[0148]

[0149] In equations (32) and (33): c P —Isobaric molar heat capacity of the working fluid / J·mol -1 ·K -1 c V —Molar heat capacity of the working fluid at constant volume / J·mol -1 ·K -1 ;

[0150] Assuming that steam is an ideal gas, the corresponding ideal gas law is shown in equations (34) and (35):

[0151]

[0152] In equations (34) and (35): R g —Gas constant / J·kg -1 ·K -1 ;

[0153] The relationship between the mass flow rate of the gas bomb and the pressure is shown in equations (36) and (37):

[0154]

[0155] Substituting the change in mass of the gas bomb obtained in step 6 into equations (36) and (37), the new value of the gas bomb pressure P is calculated. v1 * P v2 * .

[0156] Step 8: Substitute the new value of the gas bomb pressure obtained in Step 7 into equations (1)-(2) to calculate the new value of the gas bomb temperature T. V1 * T V2 * .

[0157] Step 9: Calculate the updated convective heat transfer coefficient h using equation (9). sen Substitute the new values ​​of the vapor bomb temperature obtained in step 8 into equations (5) and (6) to update the vapor-liquid boundary conditions, and calculate the new value of the liquid bomb temperature T using the energy equation of the liquid bomb shown in equation (3) and the initial and boundary condition equations (4)-(6). l * .

[0158] Step 10: Change the new temperature value T of the gas bomb obtained in Step 8. V1 * T V2 * With a given vapor chamber temperature T V1 T V2 The comparison is iterated, and the convergence criterion is set to an error of less than 10. -4 If the condition is met, the iteration stops. If not, steps 4-10 are repeated until the iteration requirements are met, and the new value of the vapor bomb temperature T is calculated. V1 * T V2 * and the new value of liquid bullet temperature T l * .

[0159] Step 11: Calculate the sensible heat transferred into and out of the liquid bomb, and calculate the thermal resistance of the pulsating heat pipe.

[0160] The sensible heat generated by the liquid bomb due to unidirectional convection can be calculated using equations (38) and (39):

[0161]

[0162] In equations (38) and (39): Q h —Sensible heat transferred by the liquid bomb / W; Q c —Sensible heat transferred from the liquid bomb / W; Tl,i —Liquid bullet temperature / K;

[0163] In steady state, the thermal resistance of the pulsating heat pipe can be calculated using (40)-(42):

[0164]

[0165] In equations (40)-(42): R—thermal resistance / K·W -1 ; —Average sensible heat transferred by the liquid bomb / W; —Average sensible heat transferred from the liquid bomb / W; —Average condensing heat / W; —Average heat of vaporization / W;

[0166] Step 12: Output the calculation results. The output includes the temperature and pressure of the vapor bomb, the temperature distribution and location of the liquid bomb, and the calculated mass of the vapor bomb, liquid film length, latent heat, sensible heat, and thermal resistance of the pulsating heat pipe. These results can be used to perform simple calculations and analyses on the flow characteristics such as oscillation height and oscillation velocity of liquid bombs with spaced capillary wick pulsating heat pipes, as well as heat transfer performance such as heat transfer and thermal resistance. The calculation results can also be plotted.

[0167] The above are preferred embodiments of this application, used only to illustrate the technical solution of the present invention. However, the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for calculating heat transfer in a spaced capillary pulsating heat pipe, characterized in that, Includes the following steps: Obtain the heat pipe size and structural parameters and the capillary wick structural parameters, and construct a pulsating heat pipe model; In the pulsating heat pipe model, two initial temperature values ​​for the gas bomb are preset, a functional relationship between the gas bomb temperature and pressure is constructed, and an initial pressure value for the gas bomb is calculated based on the functional relationship between the gas bomb temperature and pressure. Construct the liquid-bomb energy equation, and calculate the liquid-bomb temperature distribution based on the liquid-bomb energy equation and the corresponding initial and boundary conditions; A liquid-elastic momentum equation for a pulsating heat pipe with a spaced capillary wick is constructed. The shear stresses of the smooth pipe section and the capillary wick-covered pipe section are obtained respectively. Based on the liquid-elastic momentum equation for the pulsating heat pipe with a spaced capillary wick, the shear stresses of different pipe sections, and the initial values ​​of the vapor-elastic pressure, the liquid-elastic displacement is calculated. Formulas for calculating the liquid film length of smooth tube segments and capillary core covered tube segments are constructed respectively. Based on the formulas for calculating the liquid film length of different tube segments, the corresponding liquid film lengths are obtained. Obtain the heat transfer of liquid film evaporation and condensation, and calculate the corresponding change in vapor bomb mass based on the heat transfer of liquid film evaporation and condensation respectively; Obtain the relationship between the mass flow rate and pressure of the gas bomb, and calculate the new value of the gas bomb pressure based on the relationship between the mass flow rate and pressure of the gas bomb and the obtained change in the mass of the gas bomb. Based on the functional relationship between the temperature and pressure of the gas bomb and the new value of the gas bomb pressure, the new value of the gas bomb temperature is obtained; Based on the aforementioned liquid bomb energy equation and the new value of the gas bomb temperature, the new value of the liquid bomb temperature is obtained; The new values ​​of the gas bomb temperature are compared with the given initial values ​​of the gas bomb temperature and iterated to obtain the final new values ​​of the gas bomb and liquid bomb temperatures; the sensible heat transferred into and out of the liquid bomb is obtained, and the thermal resistance of the pulsating heat pipe is calculated based on the sensible heat. The system outputs liquid bomb temperature, liquid bomb displacement, liquid film length, change in vapor bomb mass, vapor bomb pressure, vapor bomb temperature, and thermal resistance of the pulsating heat pipe to complete heat transfer calculations.

2. The heat transfer calculation method for a spaced capillary pulsating heat pipe according to claim 1, characterized in that, The functional relationship between temperature and pressure of the gas bomb is shown below: Among them, T v0 P is the initial temperature of the gas bomb. v0 γ is the initial pressure of the vapor chamber; P is the heat capacity ratio; γ is the initial pressure of the vapor chamber. v1 P v2 T is the pressure of the vapor spring; V1 T V2 These are the temperatures of the gas bomb.

3. The heat transfer calculation method for a spaced capillary pulsating heat pipe according to claim 1, characterized in that, The energy equations for the liquid explosive and the corresponding initial and boundary conditions are expressed as follows: T=T0,t=0,0<x l <L p T=T v1 ,x l =0 T=T v2 ,x l =L p Where T1 is the temperature of the liquid explosive; α l d is the thermal diffusivity; A is the cross-sectional area; d is the heat pipe diameter; L p x is the length of the liquid bullet; l h represents the position of the liquid bullet. sen T is the convective heat transfer coefficient. W T represents the wall temperature. V1 T V2 t represents the temperature of the gas bomb; π represents time; and t is a constant.

4. The heat transfer calculation method for a spaced capillary pulsating heat pipe according to claim 3, characterized in that, The expression for the fluid elasticity equation of a pulsating heat pipe with a spaced capillary wick is shown below: Where, ρ l For liquid density; ΔP b For pressure loss at the bend; L p,wick τ is the length of the liquid elastic element in the capillary core region; p,wick For the shear stress in the capillary core region; L p,smooth τ is the length of the liquid bullet in the smooth region; p,smooth For the shear stress in the smooth region; P v1 P v2 ρ is the pressure of the two air balloons; g is the acceleration due to gravity.

5. The heat transfer calculation method for a spaced capillary pulsating heat pipe according to claim 1, characterized in that, The formulas for calculating the liquid film length of smooth tube sections and capillary core covered tube sections are as follows: Formula for calculating the length of a thin liquid film in a smooth tube section: Formula for calculating the length of the thin liquid film in the capillary wick-covered section: Among them, L c,i L is the length of the liquid film in the condensation section. e,i δ is the length of the liquid film in the evaporation section. smooth δ represents the thickness of the liquid film in the smooth pipe section. wick The thickness of the liquid film in the wick; m v v is the mass of the vapor bomb; u is the velocity of the condensate in the capillary wick in the x-direction; v p ε is the fluid velocity; ρ is the porosity of the wire mesh capillary core; and ρ is the liquid density.

6. The heat transfer calculation method for a spaced capillary pulsating heat pipe according to claim 1, characterized in that, The formulas for calculating the heat transfer during liquid film evaporation and condensation are shown below: Among them, Q cond,i For heat transfer during liquid film condensation; Q evp,i For heat transfer during liquid film evaporation; h sum L is the overall heat transfer coefficient. c,i L is the length of the liquid film in the condensation section. e,i T is the length of the liquid film in the evaporation section. e T c These are the wall temperatures of the evaporation section and the condensation section, respectively.

7. The heat transfer calculation method for a spaced capillary pulsating heat pipe according to claim 6, characterized in that, The formula for calculating the rate of change of mass of the gas bomb is as follows: Where, m v1 m v2 h is the mass of the gas bomb. fg This is the latent heat of phase transition of the working fluid.

8. The heat transfer calculation method for a spaced capillary pulsating heat pipe according to claim 7, characterized in that, The process of obtaining the relationship between the mass flow rate and pressure of the gas bomb includes: constructing the energy equation and the ideal gas equation of state of the gas bomb; and based on the functional relationship between the energy equation and the ideal gas equation of state of the gas bomb, obtaining the relationship between the mass flow rate and pressure of the gas bomb, as shown below: Among them, R g P is the gas constant; v1 P v2 These represent the vapor pressure; d is the heat pipe diameter; P v0 γ is the initial pressure of the vapor chamber; L is the heat capacity ratio; e This represents the length of the liquid film in the evaporation section.

9. The heat transfer calculation method for a spaced capillary pulsating heat pipe according to claim 1, characterized in that, The formulas for calculating the sensible heat transferred into and out of the liquid bomb are as follows: Among them, Q h Sensible heat transferred to the liquid bomb; Q c The sensible heat transferred from the liquid bomb; T l,i h is the temperature of the liquid bomb. sen T is the convective heat transfer coefficient. e T c These are the wall temperatures of the evaporation section and the condensation section, respectively; L p The length of the liquid bullet.

10. The heat transfer calculation method for a spaced capillary pulsating heat pipe according to claim 9, characterized in that, The formula for calculating the thermal resistance of a pulsating heat pipe is as follows: Where R is the thermal resistance; The average sensible heat transferred to the liquid bomb; The average sensible heat transferred from the liquid bomb; Average condensation heat; This represents the average heat of evaporation. The average sensible heat; This represents the average latent heat.

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