Pulsating heat pipe heat transfer calculation method capable of adjusting inclination angle and liquid filling rate

Abstract

The invention discloses a heat transfer calculation method for pulsating heat pipes with adjustable inclination angles and liquid filling rates. The heat transfer performance of the pulsating heat pipes with different inclination angles and liquid filling rates is researched by adopting a numerical method; calculating the heat transfer process by solving the energy equation of the steam bomb and the energy and momentum equation of the liquid bomb, so as to predict the pulsation phenomenon of the working medium in the pulsating heat pipe; on the basis of a momentum heat mass transfer model, calculating the phase change heat transfer capacity through film condensation and a down-flow film boiling heat transfer coefficient, investigating the influence of different inclination angles on the liquid film thickness and the down-flow film speed, and increasing the influence of the down-flow film on the liquid elastic length; and the liquid bomb pulsation condition of the pulsating heat pipe under different inclination angles and different liquid filling rates is researched, and then the heat transfer performance of the pulsating heat pipe is calculated. The working heat transfer performance of the pulsating heat pipes with different inclination angles and liquid filling rates and the motion state of the working medium are analyzed and calculated, and guidance is provided for parameter development and engineering application of the pulsating heat pipes.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of phase change heat transfer equipment, and particularly relates to a pulsating heat pipe heat transfer calculation method capable of adjusting an inclination angle and a liquid filling rate. BACKGROUND

[0002] The pulsating heat pipe is pushed to oscillate by the steam pressure difference caused by the latent heat transfer of the evaporation section and the condensation section, and becomes a heat dissipation device with great potential in the electronic cooling field due to the characteristics such as no need of a wick, various pipe processing forms, and excellent heat transfer performance. With the development of the portability and integration of electronic components, the pulsating heat pipe tends to be designed and processed in a small size. As a high-efficiency heat dissipation device, the pulsating heat pipe couples the phase change heat transfer and the oscillation heat transfer in the micro channel.

[0003] In the research on the heat transfer performance of the pulsating heat pipe, it is found that the inclination angle and the liquid filling rate have a significant influence on the system performance. However, the regulation range of the inclination angle and the liquid filling rate is still limited at present, and the experimental conditions are mostly concentrated in a fixed angle or a single liquid filling rate, so that the fine control of the working medium motion state in the pipe is difficult to realize. This limitation significantly increases the uncertainty of the liquid bullet motion and the heat transfer coefficient calculation, so that the existing theory is difficult to comprehensively explain the complex phenomena observed in the experiment, thereby hindering the in-depth understanding of the heat transfer mechanism of the pulsating heat pipe. SUMMARY

[0004] To solve the problems in the prior art, the application provides a pulsating heat pipe heat transfer calculation method capable of adjusting the inclination angle and the liquid filling rate, and the transient heat transfer flow characteristics under the conditions of different inclination angles and liquid filling rates of the pulsating heat pipe can be calculated. The temperature, pressure and mass change of the bullet are calculated by numerical simulation of the pulsating heat pipe with different inclination angles and liquid filling rates, the amplitude, temperature distribution and velocity distribution of the liquid bullet are calculated, and then the convective heat transfer coefficient, the film condensation and the falling liquid film boiling heat transfer coefficient are obtained. The heat transfer performance of the pulsating heat pipe with different inclination angles and liquid filling rates is analyzed and calculated, and guidance is provided for the parameter design and engineering application development of the pulsating heat pipe.

[0005] To achieve the above object, the application provides the following scheme. A pulsating heat pipe heat transfer calculation method capable of adjusting the inclination angle and the liquid filling rate, comprising: S1. establishing a pulsating heat pipe model, and determining the working medium in the heat pipe, the evaporation section and the condensation section temperature; S2. determining the initial liquid film thickness and the initial bullet temperature of the pulsating heat pipe model; S3. calculating the liquid bullet temperature according to the evaporation section and the condensation section temperature; S4. Calculate the initial gas bomb pressure based on the initial gas bomb temperature, calculate the liquid bomb displacement based on the gas bomb pressure, and calculate the gas bomb pressure based on the liquid bomb displacement and the liquid bomb temperature; S5. Based on the film condensation model, calculate the thickness of the condensate film, and calculate the length of the wall liquid film and the liquid bullet length based on the thickness of the condensate film. Calculate the phase change heat transfer through the film condensation and falling film boiling heat transfer coefficients, and then solve for the steam mass change caused by evaporation and condensation through latent heat calculation. Calculate the steam bullet pressure based on the amount of steam mass change. S6. Calculate the temperature of the gas bomb based on the pressure of the gas bomb, compare the temperature of the gas bomb with the initial temperature of the gas bomb, and if the difference satisfies the first relative error, proceed to step S6; otherwise, return to S2 to determine the initial temperature of the gas bomb. S7. Update the liquid bullet temperature distribution based on the gas bullet temperature and calculate the theoretical thickness of the liquid film. Compare the theoretical thickness of the liquid film with the initial liquid film thickness. If the difference satisfies the second relative error, proceed to step S7. If not, return to S2 to determine the initial liquid film thickness. S8. Calculate the sensible heat and latent heat transferred into and out of the liquid bomb based on the displacement of the liquid bomb and the temperatures of the evaporation section and the condensation section, and calculate the flow thermal resistance of the pulsating heat pipe.

[0006] Optionally, in S3, a liquid-bomb energy equation is constructed, and the liquid-bomb temperature in the energy equation is solved according to the finite difference scheme of the initial conditions and the gas-liquid interface boundary conditions to obtain the liquid-bomb temperature. The liquid-bomb energy equation is related to the wall temperature, which is obtained based on the temperatures of the evaporation section and the condensation section.

[0007] Optionally, in S4, the displacement of the liquid-propellant is calculated based on the initial vapor chamber pressure. A liquid-propellant momentum equation is constructed based on the current vapor chamber pressure, where the momentum equation represents the relationship between momentum change and pressure, gravity, and shear stress.

[0008] Optionally, in S5, the change in steam mass is obtained based on the displacement of the liquid explosive, and the steam explosive pressure is calculated based on the change in steam mass, including: Based on the Nusselt film condensation model, the thickness of the condensate film is calculated, followed by the length of the liquid film on the wall and the length of the liquid bomb. The phase change heat transfer is calculated using the heat transfer coefficients of film condensation and falling film boiling, and the steam mass change caused by evaporation and condensation is solved using latent heat calculation. The lengths of the liquid film in the condensation and evaporation sections are obtained based on the liquid bomb displacement. The latent heat of vaporization and condensation are calculated based on the overall heat transfer coefficient, liquid film length, bomb temperature, and the temperatures of the evaporation and condensation sections. The rate of change of steam mass caused by evaporation and condensation is calculated using the latent heat of vaporization, the latent heat of condensation, and the liquid bomb displacement. The energy equation of the bomb is constructed based on the rate of change of steam mass and the first law of thermodynamics to calculate the bomb pressure.

[0009] Optionally, S7 updates the heat transfer coefficient of the wall liquid film based on the changes in density, viscosity, and specific heat capacity caused by the temperature of the vapor bomb; updates the phase change heat transfer coefficient based on the changes in the liquid bomb temperature, the specific volume difference between the vapor and the liquid; updates the gas-liquid interface conditions and calculates the liquid bomb temperature distribution based on the heat transfer coefficient of the wall liquid film and the phase change heat transfer coefficient; obtains the average temperature and average velocity of the liquid bomb based on the liquid bomb temperature distribution, and calculates the theoretical thickness of the liquid film.

[0010] Optionally, in S8, the sensible heat, latent heat, and thermal resistance of the liquid bomb are calculated for both input and output.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Under the premise of ensuring the calculation speed and accuracy of the model, the heat transfer model inside the heat pipe is reasonably simplified, and the iteration process is simple and has good convergence. By iterating the temperature of the vapor spring and the thickness of the liquid film on the left and right sides of the pulsating heat pipe, the phase change heat transfer coefficient can be calculated more accurately, and the heat transfer rate can be predicted. (2) The present invention can calculate the motion state of the working fluid in the pulsating heat pipe, including velocity distribution, temperature distribution, amplitude, etc.; (3) The output can provide simpler and clearer result diagrams and motion diagrams, which can provide ideas and data references for the design of pulsating heat pipes with different tilt angles and filling rates; (4) Based on the momentum-heat-mass transfer model, the phase change heat transfer is calculated by the heat transfer coefficient of film condensation and falling liquid film boiling. The effects of different tilt angles on liquid film thickness and falling liquid film velocity are investigated, and the effect of falling liquid film on liquid blast length is added, so as to calculate the heat transfer performance of pulsating heat pipe more accurately. Attached Figure Description

[0012] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a flowchart of the heat transfer calculation method for a pulsating heat pipe with adjustable tilt angle and filling rate according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the calculation of the falling film flow in an embodiment of the present invention. Detailed Implementation

[0014] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] Example 1 like Figure 1 As shown, this invention provides a method for calculating heat transfer in a pulsating heat pipe with adjustable tilt angle and filling rate, comprising: Step 1: Establish a pulsating heat pipe model, determine the dimensional and structural parameters of the pulsating heat pipe, and divide the pulsating heat pipe into evaporation and condensation sections. Select the working medium inside the pulsating heat pipe, determine the relevant parameters of the selected working fluid properties, and assume the initial liquid film thickness; give the wall temperatures of the evaporation and condensation sections as follows: , Assume the initial temperatures of the left and right gas bombs are respectively... , Construct the energy equation of the liquid bomb to calculate its temperature; The temperature distribution in the liquid bomb is derived from the liquid bomb energy equation shown in equation (1). The liquid bomb temperature in equation (1) is solved using the finite difference scheme of the corresponding initial conditions (2) and gas-liquid interface boundary conditions (3) and (4). : MERGEFORMAT (1) MERGEFORMAT (2) MERGEFORMAT (3) MERGEFORMAT (4) In equations (1)-(4): Thermal diffusivity / m 2 ·s -1 ; The temperature of the liquid explosive is given in K. Time / s; The coordinates are in meters along the direction from the condensation section to the evaporation section. The convective heat transfer coefficient is given by W·m. -2 ·K -1 ; Heat pipe diameter / m; Thermal conductivity of the working fluid / W·m -1 ·K -1 ; Cross-sectional area / m 2 ; Wall temperature / K; The initial temperature of the liquid bomb is given in K. The length of the liquid bullet is in meters. The temperature of the gas bomb on the left is in K. Temperature of the gas bomb on the right (K) The wall temperature is related to the position of the liquid bomb, and can be determined by equations (5) and (6). : MERGEFORMAT (5) MERGEFORMAT (6) In equations (5) and (6): Temperature of the evaporation section wall in K; The condensation section wall temperature is in K. The displacement is the fluid elastic displacement in meters.

[0017] The convective heat transfer coefficient of the working fluid inside the pulsating heat pipe is calculated using equation (7). : MERGEFORMAT (7) In equation (7): For Nusselt numbers; It is the Reynolds number; It is a Prandtl number.

[0018] Step 2: Calculate the initial vapor chamber pressure according to equations (8) and (9). , The initial pressure of the vapor chamber is calculated and used as the initial value of the pressure. Updates and iterations are then performed based on this initial value. MERGEFORMAT (8) MERGEFORMAT (9) In equations (8) and (9): Initial steam temperature in K; Initial steam pressure (Pa); The pressure of the vapor spring on the left is in Pa. The pressure on the right side is the vapor spring pressure in Pa. This is the heat capacity ratio.

[0019] Step 3: Construct the momentum equation of the liquid bullet and calculate its displacement. In the momentum equation of a liquid bullet, the terms on the left represent the change in momentum, and the terms on the right are represented as pressure, gravity, and shear stress terms respectively: MERGEFORMAT (10) In formula (10): working fluid density / kg·m -3 ; Pressure loss at the bend / Pa; Shear stress / Pa; The initial conditions for a pulsating heat pipe include: MERGEFORMAT (11) MERGEFORMAT (12) MERGEFORMAT (13) MERGEFORMAT (14) MERGEFORMAT (15) In equations (11)-(15): Initial liquid propellant position / m; The length of the liquid film in the evaporation section is in meters. Pressure loss at bend for: MERGEFORMAT (16) In equation (16): This is the pressure loss coefficient; velocity / m·s -1 Shear stress is solved using equations (17) and (18). The coefficient of friction of fluid flow in the pipe is : MERGEFORMAT (17) MERGEFORMAT (18) In equations (17) and (18): coefficient of friction The displacement of the hydraulic elastic element can be calculated based on the above equations. .

[0020] Step 4: Using the Nusselt film condensation model, calculate the thickness of the condensate film, and then calculate the length of the liquid film on the wall and the length of the liquid blister; calculate the phase change heat transfer using the heat transfer coefficients of film condensation and falling film boiling, and then solve for the change in steam mass caused by evaporation and condensation using latent heat calculation. (See schematic diagram below.) Figure 2 : The thickness of the condensate film was calculated using the Nusselt film condensation model: MERGEFORMAT (19) In equation (19): Condensate film thickness / m; Viscosity of the working fluid (kg·m) -1 ·s -1 ; The average length of the liquid film in the condensation section is given in meters.

[0021] Due to gravity, the downward flow velocity and average velocity of the liquid film are: MERGEFORMAT (20) MERGEFORMAT (21) In equations (20) and (21): The velocity of the liquid bullet moving downwards / m·s -1 ; The average velocity of the liquid bullet moving downwards / m·s -1 .

[0022] When the liquid bomb flows through the channel, a liquid film remains on the wall. When the gas-liquid interface of the liquid bomb is in the evaporation section, the length of the liquid film gradually increases as the liquid bomb moves towards the condensation section; when the liquid bomb moves towards the evaporation section, the length of the liquid film gradually decreases, and simultaneously, the thin liquid film evaporates, causing the liquid film length to gradually decrease. When the gas-liquid interface of the liquid bomb is in the condensation section, only evaporation causes the length of the liquid film to decrease. The length of the thin liquid film on the wall is calculated using equation (22): MERGEFORMAT (22) In equation (22): The length of the liquid film in the condensation section is in meters. The length of the liquid film in the evaporation section is in meters. Steam mass / kg.

[0023] The average heat transfer coefficient of liquid film condensation was calculated using the Nusselt film condensation model. MERGEFORMAT (23) In equation (23): The average heat transfer coefficient of the liquid film is / W·m -2 ·K -1 ; Calculate the boiling heat transfer coefficient of the falling liquid film in the evaporation section: MERGEFORMAT (24) MERGEFORMAT (25) MERGEFORMAT (26) In equations (24)-(26): Liquid film mass flow rate / kg·s -1 ; The cross-sectional area of ​​the thin liquid film / m 2 ; The mass flow rate of the liquid film per unit length is kg·m. -1 ·s -1 ; is the Reynolds number of the thin liquid film.

[0024] Decrease the liquid film boiling heat transfer coefficient h e The conversion coefficients are organized into dimensionless form, allowing experimental data to be correlated with the introduced correction factors using dimensional combinations from Nusselt's theory. MERGEFORMAT (27) MERGEFORMAT (28) In equations (27) and (28): The coefficient of performance is a dimensionless heat transfer coefficient. To reduce the liquid film boiling heat transfer coefficient / W·m -2 ·K -1 ; Phase change heat transfer coefficient of gas-liquid interface condensation or evaporation Determined using the Schlager model: MERGEFORMAT (29) In equation (29): Phase change heat transfer coefficient / W·m -2 ·K -1 ; The fitness coefficient is set to 0.03. This represents the specific volume difference between steam and liquid; The relative mass of the working fluid is expressed in g·mol⁻¹. -1 .

[0025] The gas-liquid interface temperature is: MERGEFORMAT (30) In equation (30): The value is the temperature at the gas-liquid interface in K.

[0026] The changed length of the liquid bomb is calculated using equations (31) and (32), and the obtained changed length of the liquid bomb is then used in equation (10) for the next stage of iteration. MERGEFORMAT (31) MERGEFORMAT (32) In equations (31) and (32): The length of the changed liquid explosive is given in meters. The initial liquid bullet length is given in meters. The length of the liquid-gel section on the left is given in meters. The length of the liquid bomb in the left evaporation section is given in meters. The length of the liquid-gel section on the right is given in meters. The length of the liquid bomb in the evaporation section on the right is given in meters. The cross-sectional area of ​​the thin liquid film on the left is / m 2 ; The cross-sectional area of ​​the thin liquid film on the right is / m 2 .

[0027] When steam enters the condensing section, heat transfer occurs between the steam and the condensing section wall, causing the steam to condense and its mass to decrease. When the liquid bomb enters the evaporating section, heat transfer between the liquid bomb and the evaporating section wall causes the liquid bomb to boil, increasing the steam's mass. Under certain conditions, due to the increase in steam mass and the work done on the steam by the moving liquid bomb, the steam temperature may rise above the evaporating section temperature. At this point, condensation occurs due to heat transfer between the steam and the evaporating section wall, further reducing the steam's mass.

[0028] MERGEFORMAT (33) In equation (33): The latent heat (W) for liquid film condensation and vapor condensation at the gas-liquid interface; The latent heat (W) is the heat of vaporization of liquid film and vapor-liquid interface liquid-bomb vaporization.

[0029] The rate of change in steam mass due to evaporation and condensation is calculated using equations (34) and (35): MERGEFORMAT (34) MERGEFORMAT (35) In equations (34) and (35): Latent heat of phase transition of the working fluid / J·kg -1 .

[0030] Step 5: Based on the first law of thermodynamics, construct the energy equations (36) and (37) for the gas bomb, and calculate the pressure of the gas bomb by combining them with the ideal gas law: MERGEFORMAT (36) MERGEFORMAT (37) In equations (36) and (37): The constant-pressure heat capacity of the working fluid / J·kg -1 ·K -1 ; The constant volume heat capacity of the working fluid / J·kg -1 ·K -1 .

[0031] MERGEFORMAT (38) MERGEFORMAT (39) In equations (38) and (39): Gas constant / J·mol -1 ·K -1 ; The relationship between the mass and pressure of the two gas bombs is shown in equations (40) and (41): MERGEFORMAT (40) MERGEFORMAT (41) Substitute the steam mass change obtained in step 5 into equations (40) and (41) to calculate the pressure of the steam bomb. , .

[0032] Step 6: Calculate the temperature of the gas bomb using equations (8) and (9). , Compare the results with the hypothesis. , 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; otherwise, the iteration is repeated from step 2 until the iteration requirement is met, and the vapor bomb temperature is calculated. , .

[0033] Step 7: Measure the temperature of the gas bomb in Step 6. , The changes in density, viscosity, and specific heat capacity caused by the change, as well as the momentum equation (10) of the liquid elasticity, are used to update the convective heat transfer coefficient by equation (7). ; through the temperature of the gas bomb in step 6 , The changes in vapor and liquid specific volume difference due to evaporation and condensation are updated by equation (29) to determine the phase change heat transfer coefficient at the gas-liquid interface during condensation or evaporation. In a pulsating heat pipe, the convective heat transfer coefficient and the phase change heat transfer coefficient jointly determine the temperature distribution of the liquid blast, thus affecting the heat transfer performance of the pulsating heat pipe, by influencing the flow and phase change process of the working fluid. Optimizing the calculation of the convective heat transfer coefficient and the phase change heat transfer coefficient can improve the heat transfer efficiency and stability of the pulsating heat pipe.

[0034] Step 8: The gas-liquid interface temperature changes, causing the liquid bomb to shift, which alters the gas-liquid boundary conditions (3) and (4). The updated liquid bomb temperature distribution is calculated using the liquid bomb energy equation shown in equation (1), the initial condition (2), and the changed boundary conditions (3) and (4). The theoretical liquid film thickness and the average length of the liquid film in the condensation section are calculated according to equation (19) and compared with the liquid film thickness and the average length of the liquid film in the condensation section assumed in step 1 until the error condition is met.

[0035] Step 9: Calculate the sensible heat transmitted into and out of the liquid bomb.

[0036] The heat generated by the liquid bomb due to unidirectional convection is calculated using equations (42) and (43); MERGEFORMAT (42) MERGEFORMAT (43) In equations (42) and (43): Sensible heat transferred by the liquid bomb / W; The sensible heat transferred from the liquid bomb / W; When the pulsating heat pipe is in steady state operation, the total heat transfer is calculated using equations (44), (45), and (46). Sensible heat transfer Latent heat transfer : MERGEFORMAT (44) MERGEFORMAT (45) MERGEFORMAT (46) In equations (44)-(46): Latent heat transfer rate / W; Sensible heat transfer rate (W); Total heat transfer / W.

[0037] Step 10: Output Calculation. During the periodic oscillation motion of the liquid bomb, taking the junction of the evaporation and condensation sections as the zero point, the displacement of the liquid bomb can be calculated. The temperature distribution of the liquid bomb can be solved through the energy equation, and the velocity distribution of the liquid bomb can be solved through the momentum equation. The output results are the temperature and pressure of the vapor bomb, the temperature distribution, velocity distribution, and displacement of the liquid bomb, as well as the steam mass change, sensible heat, and latent heat of the pulsating heat pipe calculated based on the above results. The steam mass change in the pulsating heat pipe is driven by the pressure difference caused by the temperature gradient between the evaporation and condensation sections, which promotes the circulation of the working fluid between the evaporation and condensation sections, thereby realizing heat transfer. Latent heat is the heat absorbed or released by the working fluid during the phase change process, and sensible heat is the heat absorbed or released by the working fluid during the temperature change process of heating or cooling. The sensible heat transfer of the liquid bomb pulsation in the pulsating heat pipe is the main heat transfer pathway. The above results can be used to perform simple calculations and analyses of the heat transfer performance of pulsating heat pipes operating with different working fluids, such as oscillation height, oscillation speed, and heat transfer, and to draw motion diagrams based on the calculation results.

[0038] The present invention provides a method for calculating the heat transfer of a pulsating heat pipe with adjustable tilt angle and filling rate. This method includes: an open-loop pulsating heat pipe consisting of an evaporation section and a condensation section; selecting the working fluid within the pulsating heat pipe and calculating the target parameters of the working fluid's properties; and using numerical methods to study the heat transfer performance of the pulsating heat pipe with different tilt angles and filling rates. The heat transfer process is calculated by solving the energy equations of the vapor bomb and the energy and momentum equations of the liquid bomb, thereby predicting the pulsation phenomenon of the working fluid in the pulsating heat pipe. Based on the momentum-heat-mass transfer model, the phase change heat transfer is calculated using the heat transfer coefficients of film condensation and falling film boiling. The effects of different tilt angles on the liquid film thickness and falling film velocity are examined, and the influence of the falling film on the liquid bomb length is added. The pulsation and heat transfer performance of the liquid bomb in pulsating heat pipes with different tilt angles and filling rates are studied, leading to a novel algorithm for calculating the heat transfer performance of the pulsating heat pipe. This invention analyzes and calculates the heat transfer performance and working fluid motion state of pulsating heat pipes with different tilt angles and filling rates, providing guidance for the parameter design, development, and engineering applications of pulsating heat pipes.

[0039] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for calculating heat transfer in a pulsating heat pipe with adjustable tilt angle and filling rate, characterized in that, include: S1. Establish a pulsating heat pipe model and determine the working fluid, evaporation section, and condensation section temperatures within the heat pipe; S2. Determine the initial liquid film thickness and initial vapor bomb temperature of the pulsating heat pipe model; S3. Calculate the liquid bullet temperature based on the temperatures of the evaporation section and the condensation section; S4. Calculate the initial gas bomb pressure based on the initial gas bomb temperature, calculate the liquid bomb displacement based on the gas bomb pressure, and calculate the gas bomb pressure based on the liquid bomb displacement and the liquid bomb temperature; S5. Based on the film condensation model, calculate the thickness of the condensate film, and calculate the length of the wall liquid film and the liquid bullet length based on the thickness of the condensate film. Calculate the phase change heat transfer through the film condensation and falling film boiling heat transfer coefficients, and then solve for the steam mass change caused by evaporation and condensation through latent heat calculation. Calculate the steam bullet pressure based on the amount of steam mass change. S6. Calculate the temperature of the gas bomb based on the pressure of the gas bomb, compare the temperature of the gas bomb with the initial temperature of the gas bomb, and if the difference satisfies the first relative error, proceed to step S6; otherwise, return to S2 to determine the initial temperature of the gas bomb. S7. Update the liquid bullet temperature distribution based on the gas bullet temperature and calculate the theoretical thickness of the liquid film. Compare the theoretical thickness of the liquid film with the initial liquid film thickness. If the difference satisfies the second relative error, proceed to step S7. If not, return to S2 to determine the initial liquid film thickness. S8. Calculate the sensible heat and latent heat transferred into and out of the liquid bomb based on the displacement of the liquid bomb and the temperatures of the evaporation section and the condensation section, and calculate the flow thermal resistance of the pulsating heat pipe.

2. The method for calculating heat transfer in a pulsating heat pipe with adjustable tilt angle and filling rate according to claim 1, characterized in that, In S3, a liquid bomb energy equation is constructed, and the liquid bomb temperature in the liquid bomb energy equation is solved according to the finite difference scheme of the initial conditions and the gas-liquid interface boundary conditions to obtain the liquid bomb temperature. The liquid bomb energy equation is related to the wall temperature, which is obtained based on the temperatures of the evaporation section and the condensation section.

3. The method for calculating heat transfer in a pulsating heat pipe with adjustable tilt angle and filling rate as described in claim 2, characterized in that, In S4, the displacement of the liquid bullet is calculated based on the initial gas bullet pressure; the momentum equation of the liquid bullet is constructed based on the current gas bullet pressure, wherein the momentum equation is the relationship between momentum change and pressure, gravity and shear stress.

4. The method for calculating heat transfer in a pulsating heat pipe with adjustable tilt angle and filling rate according to claim 3, characterized in that, In S5, the change in steam mass is obtained based on the displacement of the liquid explosive, and the steam pressure is calculated based on the change in steam mass, including: Based on the Nusselt film condensation model, the thickness of the condensate film is calculated, followed by the length of the liquid film on the wall and the length of the liquid bomb. The phase change heat transfer is calculated using the heat transfer coefficients of film condensation and falling film boiling, and the steam mass change caused by evaporation and condensation is solved using latent heat calculation. The lengths of the liquid film in the condensation and evaporation sections are obtained based on the liquid bomb displacement. The latent heat of vaporization and condensation are calculated based on the overall heat transfer coefficient, liquid film length, bomb temperature, and the temperatures of the evaporation and condensation sections. The rate of change of steam mass caused by evaporation and condensation is calculated using the latent heat of vaporization, the latent heat of condensation, and the liquid bomb displacement. The energy equation of the bomb is constructed based on the rate of change of steam mass and the first law of thermodynamics to calculate the bomb pressure.

5. The method for calculating heat transfer in a pulsating heat pipe with adjustable tilt angle and filling rate according to claim 4, characterized in that, S7 includes: The heat transfer coefficient of the wall liquid film is updated based on the changes in density, viscosity, and specific heat capacity caused by the temperature of the vapor bomb; the phase change heat transfer coefficient is updated based on the changes in the temperature of the liquid bomb and the specific volume difference between the vapor and liquid; the gas-liquid interface conditions are updated and the liquid bomb temperature distribution is calculated based on the heat transfer coefficient of the wall liquid film and the phase change heat transfer coefficient; the average temperature and average velocity of the liquid bomb are obtained based on the liquid bomb temperature distribution, and the theoretical thickness of the liquid film is calculated.

6. The method for calculating heat transfer in a pulsating heat pipe with adjustable tilt angle and filling rate according to claim 5, characterized in that, Calculate the sensible heat, latent heat, and thermal resistance of the liquid bomb as described in S8.

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