Parallel high-temperature heat pipe structure model and numerical simulation method

Abstract

The embodiment of the invention provides a parallel high-temperature heat pipe structure model and a numerical simulation method, and belongs to the technical field of nuclear energy and aerospace heat management. According to the structure model, two straight pipes are connected through a bent pipe to form a parallel loop, each straight pipe radially comprises an outer wall, a liquid absorption core and a steam area, and each straight pipe is axially divided into an evaporation section, a heat insulation section and a condensation section. Geometric and physical parameters are determined and initialized, and a starting process is simulated in stages; a two-dimensional axial symmetry model is adopted to solve heat conduction of a wall surface and a wick; after working medium phase change, an additional heat conductivity coefficient is introduced to approximate steam heat transfer; after it is detected through Knudsen number that steam establishes continuous flow, steam-liquid interface coupling calculation is carried out, three-dimensional numerical simulation is carried out on a steam area, and an N-S equation set is solved to obtain accurate temperature, pressure and flow velocity distribution. According to the invention, the problem that the starting process of the parallel heat pipe cannot be accurately simulated in the prior art is solved, particularly the complex flow at the elbow is revealed through the three-dimensional model, and a reliable simulation tool is provided for the design of the high-performance heat pipe.

Description

Technical Field

[0001] This application relates to the fields of nuclear energy and spacecraft thermal management technology, and in particular to a parallel high-temperature heat pipe structure model and numerical simulation method. Background Technology

[0002] With the increasing demand for long-cycle, high-power energy in cutting-edge fields such as deep space exploration and deep-sea development, traditional solar and chemical energy sources are no longer sufficient to meet mission requirements due to their low energy density and strong environmental dependence. Nuclear energy, with its ultra-high energy density, strong environmental adaptability, and ultra-long operating life, has become a core solution for mobile energy systems in extreme environments. Among them, heat pipe-cooled reactors, by directly embedding high-temperature metal heat pipes into solid reactor core fuel, construct an all-solid-state passive heat transfer system, which can significantly improve system safety and reliability.

[0003] High-temperature metal heat pipes, as passive heat transfer components based on the phase change of the working fluid, achieve ultra-efficient heat transfer through the evaporation-condensation cycle of liquid metal within a sealed vacuum tube. They possess advantages such as high axial heat flux density, high equivalent thermal conductivity, good isothermal properties, and compact structure, making them ideal heat transfer carriers for reactors. Therefore, conducting accurate numerical simulation studies on the transient start-up and steady-state heat transfer processes of high-temperature metal heat pipes is crucial for finding the optimal design scheme.

[0004] Currently, most publicly available heat pipe startup procedures or calculation methods are designed for single cylindrical heat pipes. For example, patent CN114154438A discloses a three-stage calculation method for cold startup of alkali metal heat pipes, and CN118627348A discloses a numerical simulation method applied to the analysis of high-temperature alkali metal heat pipes. These existing technologies generally use simplified two-dimensional axisymmetric rectangular models for calculations and simplify the simulation of the vapor zone to a set of one-dimensional differential equations, which cannot accurately reflect the actual flow and heat transfer of steam in complex structures.

[0005] In practical applications, the demand for parallel heat pipes (composed of multiple heat pipes connected by connecting components) is increasingly prominent in order to improve heat transfer power and system reliability. However, existing technologies do not address the simulation of the startup process of such parallel heat pipes. Their complex structure (especially the bends) can lead to radial secondary flow and pressure and temperature deviations in vapor flow. Traditional two-dimensional or one-dimensional models cannot accurately capture these phenomena, thus limiting the accuracy of simulation results and their engineering guidance value. Summary of the Invention

[0006] The main objective of this application is to propose a parallel high-temperature heat pipe structure model and numerical simulation method, which can accurately simulate the temperature distribution of the heat pipe outer wall, the wick region, and the vapor chamber region during the startup process of the parallel structure, as well as the three-dimensional distribution of vapor pressure, temperature, and flow rate after the continuous flow is established, providing a more realistic reference for experimental research and engineering applications.

[0007] To achieve the above objectives, one aspect of this application proposes a parallel high-temperature heat pipe structure model, including two straight pipes with identical structures and one bent pipe; The straight pipe, from radial to inner, includes a heat pipe outer wall, a liquid wick region, and a vapor region, and from axial to includes an evaporation section, an insulation section, and a condensation section connected in sequence. The bend connects the evaporation sections of the two straight pipes, forming a complete parallel loop; the radial structure of the bend is the same as that of the straight pipe.

[0008] In some embodiments, the radial structure of the bend is the same as that of the straight pipe, that is, it also includes an outer wall, a liquid-absorbing core, and a vapor zone.

[0009] In some embodiments, the outer wall of the heat pipe is made of stainless steel, and the working fluid filled in the wick region is liquid potassium metal.

[0010] In some embodiments, the liquid-absorbing core region has a porous structure.

[0011] To achieve the above objectives, another aspect of this application proposes a numerical simulation method for the startup process of a parallel high-temperature heat pipe structure model as described above, comprising the following steps: Determine the geometric parameters (such as the length of each section, the wall thickness, the bend radius, etc.) and physical property parameters (such as material density, specific heat capacity, thermal conductivity, etc.) of the parallel high-temperature heat pipe, establish a numerical model and perform mesh generation and initialization; Heat flux density is applied to the outer wall of the evaporation section for heating. The unsteady heat conduction equation of the outer wall of the heat pipe and the liquid wick region is solved using a two-dimensional axisymmetric model to obtain the temperature distribution. When the working fluid in the wick region undergoes a phase change and generates steam, the axial heat transfer effect of the steam region is added to the heat conduction equation of the wick region in the form of an additional thermal conductivity coefficient for solving. The flow state of the steam zone is detected. When it is determined that the steam zone has established a completely continuous flow, the liquid core region and the steam zone are coupled and calculated at the vapor-liquid interface. Based on the coupling results, a three-dimensional numerical simulation of the steam working fluid flow and heat transfer in the steam zone is performed until the temperature field converges.

[0012] In some embodiments, when a solid-liquid phase change is detected in the working fluid within the wick region, an equivalent model is used to calculate the equivalent volumetric heat capacity and equivalent thermal conductivity of the wick region. The equivalent model distinguishes the physical properties of the working fluid in three states—solid, molten, and liquid—based on temperature ranges, specifically as follows: when When using a solid working fluid, the calculation is performed. when When using a molten working fluid, the calculation is performed. when When using liquid working fluid, calculations are performed. in, The melting point temperature of the working fluid. This refers to the phase transition temperature range.

[0013] In some embodiments, for alkali metal working fluids: Potassium has a melting point of 63.5℃ (336.65K). Sodium has a melting point of 97.8℃ (370.95K). The melting point of lithium is 180.5℃ (453.65K).

[0014] In some embodiments, the additional thermal conductivity The calculation formula is:

[0015] in, Where is the radius of the steam zone. The radius of the outer wall of the suction core. For latent heat of vaporization, The molecular mass of the working fluid. The dynamic viscosity of the working fluid. This is the universal gas constant. For steam pressure, For steam temperature, It is a Knudsen number.

[0016] In some embodiments, detecting the flow state of the steam zone includes: Calculate the Knudsen number of the working medium in the steam zone. ,when When the flow is complete, it is determined that a continuous flow has been fully established.

[0017] In some embodiments, the coupling calculation of the liquid absorption core region and the vapor region at the vapor-liquid interface includes: Based on molecular dynamics theory, the net mass exchange rate of evaporation / condensation is calculated according to the pressure and temperature on both sides of the vapor-liquid interface. ; Based on the net mass exchange rate Calculate the thermal flow boundary conditions of the input steam region. ; Heat flow boundary conditions With the speed of sound limit of heat pipes Compare the values ​​and take the smaller value as the final heat flow boundary condition; Based on the final thermal flux boundary condition, calculate the initial normal phase velocity of steam at the vapor-liquid interface. , which serves as the entry boundary condition for three-dimensional numerical simulation.

[0018] In some embodiments, the uniform temperature of the vapor zone is solved by establishing a mass conservation equation at the vapor-liquid interface and using Newton's iterative method. Then, the net mass exchange rate is calculated. .

[0019] In some embodiments, the three-dimensional numerical simulation of the steam working fluid flow and heat transfer in the steam zone includes: Solve the three-dimensional steady-state governing equations for the vapor region, including the continuity equation, momentum equation, energy equation, ideal gas law, and Clausius-Clapeyron equation; wherein the momentum equation neglects the change of viscosity with position, and the energy equation considers the work done by pressure and viscous forces.

[0020] In some embodiments, the three-dimensional steady-state control equations are discretized and solved using the finite element method. The solution process includes: A1. Consistent temperature obtained using coupled calculations and initial normal phase velocity Initialize the steam zone; A2. Solve the energy equation for the steam region to obtain the temperature distribution of the steam region; A3. Using the temperature distribution, solve the continuity equation and momentum equation to obtain the pressure and velocity distribution in the steam zone; A4. Iterate through steps A2 and A3 until the temperature field converges.

[0021] The embodiments of this application include at least the following beneficial effects: The parallel heat pipe used in this invention consists of a bent tube connecting two straight tubes with identical structures. A single straight tube is radially divided into a heat pipe wall, a wick, and a vapor chamber, and axially divided into an evaporation section, an adiabatic section, and a condensation section. The bent tube serves as the adiabatic section of the parallel heat pipe, structurally connecting the evaporation sections of the two straight tubes. It is also radially divided into a heat pipe wall, a wick, and a vapor chamber. During stable operation of the heat pipe, the liquid working fluid in the wick region and the vapor working fluid in the vapor chamber continuously undergo phase change, circulating and transferring heat, achieving good temperature uniformity while achieving heat transfer. Regarding heat transfer performance, due to the presence of the bent tube, the parallel heat pipe contains more working fluid than two independently operating straight cylindrical heat pipes, enabling it to withstand greater input power and have better heat transfer capacity, thus shortening heat transfer time and improving heat transfer efficiency. Regarding start-up performance, more working fluid would extend the heat pipe's start-up time to some extent, but the parallel heat pipe used in this invention does not connect the condensation sections of the two straight tubes, so the impact on start-up performance is minimal.

[0022] Furthermore, this application provides a numerical simulation method for the startup process of a parallel high-temperature heat pipe structure model. The startup process of the parallel high-temperature metal heat pipe is divided into multiple stages, with each stage establishing a mathematical and physical model that conforms to the actual physical process. The numerical simulation of heat transfer phenomena on the heat pipe wall and in the wick region of the parallel high-temperature heat pipe is achieved through regional two-dimensional heat conduction calculations; the heat transfer of steam flow in the vapor region is obtained by calculating the three-dimensional Navier-Stokes equations. The phase change heat transfer of the working fluid at the vapor-liquid interface, with the liquid working fluid evaporating in the evaporation section and the steam working fluid condensing in the condensation section, is the key to achieving the coupling of these two parts. This numerical simulation method utilizes mass flow conservation and energy conservation to realize the complete startup process of a parallel high-temperature metal heat pipe, clearly demonstrating the heat transfer characteristics of the parallel heat pipe and providing a reference for experimental or reactor applications. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the five stages of the parallel high-temperature heat pipe startup in the embodiments of this application; Figure 2 This is a flowchart of the parallel high-temperature heat pipe startup procedure in the embodiments of this application; Figure 3 This is a flowchart of the steps of the numerical simulation method applied to the startup process of a parallel high-temperature heat pipe structure model in the application embodiments. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit it. In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with those of this application; they are merely examples of apparatuses and methods consistent with some aspects of the embodiments of this application as detailed in the appended claims.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0026] See Figure 1 This embodiment provides a parallel high-temperature heat pipe structure model. The model includes two straight pipes with identical structures and a bent pipe connecting them.

[0027] The straight pipe, from radial direction from the outside to the inside, includes the outer wall of the heat pipe, the liquid wick region, and the vapor region.

[0028] The straight pipe comprises, from the axial direction, an evaporation section, an insulation section, and a condensation section connected in sequence.

[0029] The bend connects the evaporation sections of the two straight tubes, forming a complete parallel loop. The radial structure of the bend is the same as that of the straight tube, that is, it also includes an outer wall, a liquid absorption core, and a vapor zone.

[0030] In some embodiments, the outer wall of the heat pipe is made of stainless steel, and the working fluid filled in the wick region is liquid potassium metal. The wick region has a porous structure with a porosity of [missing information]. .

[0031] Based on the above structural model, see Figure 3 This embodiment also provides a startup program for the above-mentioned parallel high-temperature heat pipe structure model, which includes the following steps: Step S1: Determine the geometric parameters (such as the length of each section, the wall thickness, the bend radius, etc.) and physical property parameters (such as material density, specific heat capacity, thermal conductivity, etc.) of the parallel high-temperature heat pipe, establish a numerical model, and perform mesh generation and initialization. The initialization state is usually at room temperature (such as 30℃), at which time the working fluid is solid and the vapor zone is a vacuum.

[0032] Step S2: Apply heat flux density to the outer wall of the evaporation section for heating, and use a two-dimensional axisymmetric model to solve the unsteady Fourier heat conduction equation for the outer wall of the heat pipe and the liquid wick region to obtain the temperature distribution.

[0033] In some embodiments, when a solid-liquid phase transition is detected in the working fluid within the wick region, an equivalent model is used to calculate the equivalent volumetric heat capacity and equivalent thermal conductivity of the wick region. This model is based on a temperature range (in terms of melting point). and phase transition range The physical properties of the working fluid in its solid, molten, and liquid states (as boundaries) are used to more accurately describe the phase transition process.

[0034] Step S3: After the working fluid in the wick region undergoes a phase change and generates steam, the axial heat transfer effect of the steam region is added to the heat conduction equation of the wick region in the form of an additional thermal conductivity coefficient for solving, so as to approximately consider its heat transfer contribution when the steam has not fully established a continuous flow.

[0035] In some embodiments, the additional thermal conductivity The calculation comprehensively considers steam properties, geometry, and flow state (Knudsen number). The calculation formula is as follows:

[0036] Step S4: Detect the flow state of the steam zone. When it is determined that the steam zone has completely established a continuous flow, couple the liquid core area and the steam zone at the vapor-liquid interface for calculation. Based on the coupling results, perform a three-dimensional numerical simulation of the steam working fluid flow and heat transfer in the steam zone. Iterate the calculation until the temperature field converges.

[0037] In some embodiments, the Knudsen number of the working fluid in the steam zone is calculated. The flow state is determined by the ratio of mean free path to characteristic dimension. When the flow is complete, it is determined that a continuous flow has been fully established.

[0038] In step S4, coupled computation is a key technology, specifically including: Step S4.1: Based on molecular dynamics theory, calculate the net mass exchange rate of evaporation / condensation according to the pressure and temperature on both sides of the vapor-liquid interface. ; Step S4.2: Based on the net mass exchange rate Calculate the thermal flow boundary conditions of the input steam region. ; Step S4.3: Set the heat flux boundary conditions With the speed of sound limit of heat pipes Compare the values ​​and take the smaller value as the final heat flow boundary condition; Step S4.4: Based on the final thermal flux boundary conditions, calculate the initial normal phase velocity of the steam at the vapor-liquid interface. , which serves as the entry boundary condition for three-dimensional numerical simulation.

[0039] In some embodiments, the three-dimensional numerical simulation in step S4 involves solving the three-dimensional steady-state governing equations of the steam region, including the continuity equation, momentum equation, energy equation, ideal gas law, and Clausius-Clapeyron equation. To accurately capture the pipe bending effect, the momentum and energy equations are specifically treated (e.g., neglecting viscosity variations with position and considering viscous dissipation). The finite element method is preferably used for discretization and iterative solution.

[0040] The following is a detailed description and explanation of the embodiments of the present invention, in conjunction with specific implementation methods.

[0041] like Figure 1 and Figure 2 As shown, this embodiment provides a parallel high-temperature heat pipe structure model and startup procedure for heat transfer in space reactors, specifically including: Step 1: Determine the geometric model of the parallel high-temperature heat pipe. Specifically, the high-temperature heat pipe is divided into an evaporation section, a condensation section, and an adiabatic section (a straight pipe connecting the evaporation and condensation sections on the same side / a bent pipe connecting the evaporation sections on different sides). Determine the straight pipe lengths, distances between the two pipes, and bend radii for each of the evaporation, condensation, and adiabatic sections. Radially, determine the thickness of the heat pipe's outer wall, the thickness of the wicking region, and the thickness of the vapor region. Determine the liquid metal working fluid and the outer wall material of the parallel high-temperature heat pipe; for example, potassium may be chosen as the working fluid, and stainless steel as the outer wall material. To simplify the calculation process, this embodiment uses a two-dimensional axisymmetric model to numerically simulate the startup process of the parallel high-temperature heat pipe.

[0042] Step 2: Establish a numerical model of the parallel high-temperature heat pipe based on the geometric parameters in Step 1 and perform mesh generation. Initialize the parallel high-temperature heat pipe at room temperature (30℃, 303.15K). Before heating the evaporation section of the parallel high-temperature heat pipe, the working fluid in the wick region is solid at room temperature, and the vapor region is in a vacuum state. At the start-up process, apply a reasonable heat flux density to the evaporation section on the outer wall of the heat pipe. The temperature of the evaporation section tube wall rises, and heat is conducted through the tube wall to the wick and the solid metal working fluid within it. The temperature increases, but the working fluid does not undergo a phase change. In the first stage, such as... Figure 1 As shown in the first stage, the high-temperature liquid metal heat pipe model can be regarded as a two-dimensional axisymmetric model. The heat pipe wall satisfies the two-dimensional unsteady Fourier heat conduction equation, and the heat conduction and heat capacity matrices are calculated using the finite element method. In cylindrical coordinates, the equation is:

[0043] in, Density, kg / m³ 3 ; Specific heat capacity, J / (kg·K); is the thermal conductivity, W / (m·K).

[0044] As heating continues in the evaporation section of the high-temperature heat pipe, the working fluid near the pipe wall inside the wick gradually undergoes a phase change, entering the second stage of the start-up process, such as... Figure 1 The second stage is shown in the diagram. Solid-liquid phase transition detection is performed in the wick region. Once the temperature of a certain computational unit enters the phase transition range, a solid-liquid phase transition switch is triggered, and an exothermic boundary condition is applied in the condensation section. Part of the metallic working fluid melts from a solid state to a liquid state after passing through a molten state at high temperature, while the remaining working fluid remains solid. The vapor chamber maintains a vacuum state, and the interface between the wick and the vapor zone can be considered an adiabatic boundary. In this stage, since the working fluid in the wick region exists in three forms—solid, molten, and liquid—it is necessary to distinguish the physical properties of these three forms. An equivalent model is used to distinguish the equivalent volumetric heat capacity and equivalent thermal conductivity of the three forms of working fluid through three temperature ranges. The wick satisfies the two-dimensional unsteady Fourier heat conduction equation, and the thermal conductivity and heat capacity matrices are calculated using the finite element method. In cylindrical coordinates, the equation is:

[0045]

[0046]

[0047] in, The density of the working fluid is kg / m³. 3 ; The specific heat capacity of the working fluid is J / (kg·K); The thermal conductivity is W / (m·K); The porosity of the porous structure of the liquid absorption core; Latent heat of fusion, J / kg; K is the melting point temperature. This represents the phase transition temperature range. Subscript 's' indicates a solid working medium, subscript 'l' indicates a liquid working medium, and subscript 'w' indicates a wick.

[0048] In step 2, the temperature of the evaporation section of the heat pipe's outer wall and wick region increases rapidly with heating time, while the temperature of the adiabatic and condensation sections does not change significantly. This is because the thermal conductivity is still relatively low at this point, and the radial length of the heat pipe is much smaller than its axial length. Therefore, the radial heat transfer effect in the evaporation section is more pronounced than the axial heat transfer effect.

[0049] Step 3: Continue heating the evaporation section of the high-temperature heat pipe. The amount of liquid working fluid in the wick increases, gradually filling the adiabatic and condensation sections. The liquid working fluid has reached the interface between the wick and the vapor zone, entering the third stage of the startup process. Figure 1 As shown in the third stage, the liquid working fluid inside the wick begins to evaporate in the evaporation section, filling the steam chamber with vapor. The flow of the vapor working fluid within the steam chamber is a free molecular flow.

[0050] Heating continues in the high-temperature heat pipe evaporation section, causing a continuous increase in steam. Within the steam zone, the working fluid flow near the evaporation section is continuous, while near the condensation section it remains a free molecular flow, entering the fourth stage of the start-up process. Figure 1 As shown in the fourth stage.

[0051] In the third and fourth stages of the startup process, due to the low steam temperature and slow flow rate in the steam zone, and the fact that it has not yet fully entered a continuous flow state, it is difficult to calculate the temperature, flow rate, and pressure of the steam in the steam zone. Based on the conservation of infinitesimal mass and energy of the steam working fluid in the steam zone, combined with the characteristics of free molecular flow and one-dimensional incompressible laminar flow, the axial heat transfer process of the steam can be fitted into an axial additional thermal conductivity coefficient and added to the heat conduction equation of the wicking region for calculation. The heat conduction equation of the wicking region is solved, and the interface temperature between the wicking region and the steam zone is considered as the temperature of the steam zone. The formula for calculating the additional thermal conductivity is as follows:

[0052] in, Let be the radius of the steam zone, in meters. Let be the radius of the outer wall of the suction core, in meters (m).

[0053] The Knudsen number, the ratio of mean free path to the diameter of the vapor zone, is used to distinguish between continuous flow and free molecular flow. Continuous flow is detected in the last grid cell at the interface between the wick region and the vapor zone; if the transition temperature is reached... Then the working fluid in the steam zone will establish a completely continuous flow.

[0054]

[0055]

[0056] in, The value is the molecular weight of the working fluid, in g / mol. Here is the universal gas constant, J / (K·mol); Let be the dynamic viscosity of the working fluid, Pa·s; The density of the working fluid is kg / m³. 3 ; denoted as the diameter of the steam zone, in meters (m).

[0057] Step 4: Once the working fluid in the steam zone has fully established a continuous flow, the process enters the fifth stage of startup, such as... Figure 1 As shown in the fifth stage. Since the evaporation and condensation of the working fluid occur respectively at the interface between the wick region and the vapor region (i.e., the vapor-liquid interface), the evaporation section and the condensation section, the wick and the vapor region need to be coupled before calculating the flow and heat transfer of the working fluid in the vapor region. According to molecular dynamics theory, the net mass exchange rate of evaporation / condensation can be obtained. :

[0058] in, The evaporation / condensation coefficient is a constant. The pressure of the working fluid at the vapor-liquid interface, in Pa; The pressure of the steam working fluid is expressed in Pa. The temperature of the working fluid at the vapor-liquid interface, in K; K represents the uniform temperature of the steam working fluid.

[0059] In coupled calculations, the temperature in the steam zone is treated as a uniform temperature. Mass is conserved at the vapor-liquid interface for both liquid and vapor working fluids.

[0060]

[0061] Rewrite the mass conservation equation with respect to the uniform temperature of the steam zone. function And the central difference method is used to calculate The uniform temperature of the steam zone was calculated using the Newton-Raphson iterative method. Set a reasonable error range and maximum number of iterations to ensure consistent temperature across the calculated steam zone. Accurate enough The net mass exchange rate used to calculate evaporation / condensation will be used. This is a crucial step in coupling the liquid absorption core area with the vapor zone.

[0062]

[0063]

[0064]

[0065] The heat flux boundary conditions for the input steam region can be obtained as follows:

[0066] The calculated thermal flux boundary conditions of the input steam region With the speed of sound By comparing the two values, the smaller value is selected as the true boundary condition to avoid the influence of the sound speed limit on the heat transfer of steam flow.

[0067]

[0068] in, The latent heat of vaporization of the working fluid is J·kg⁻¹; The density of the working fluid at the start of the evaporation section is kg·m⁻³. The initial working fluid temperature of the evaporation section is K; Let m be the cross-sectional area of ​​the steam zone; Specific heat ratio of the steam working fluid; is the working gas constant.

[0069] Input steam zone heat flow boundary conditions That is, the latent heat of the working fluid during evaporation in the evaporation section. Relationship with the initial normal phase velocity of steam at the vapor-liquid interface in the steam zone:

[0070] Since only the heat conduction equations for the heat pipe wall and wick region are calculated before step 4, without considering changes in pressure and velocity of the working fluid, a two-dimensional model is used to calculate the temperature distribution of the heat pipe wall and wick region. In step 4, the steam in the vapor region has entered a continuous flow state. Due to the involvement of the bend model, the steam flow at the bend will cause radial temperature and pressure deviations and generate radial secondary flow. Although this does not affect the heat transfer performance of the two straight pipes in the parallel heat pipe, in order to more accurately simulate the steam flow heat transfer and obtain its temperature, pressure, and velocity distribution, the program will perform three-dimensional numerical calculations on the steam working fluid flow heat transfer in the vapor region in step 4. It is assumed that the vapor region inside the parallel high-temperature heat pipe is experiencing ideal saturated steam flow, and the steam in the vapor region should satisfy the steady-state continuity equation, momentum equation, energy equation, ideal gas equation, and Clausius-Clapeyron equation. Among them, the momentum equation ignores the viscosity change with position, and the energy equation considers the work done by pressure and viscous forces.

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079] In some embodiments, the finite element method is used to discretize and solve the differential equations of the steam region, and the steps are as follows: a) The uniform temperature of the steam zone calculated iteratively using Newton's iteration method Initialize the temperature in the steam zone, add heat flux boundary conditions in the evaporation / condensation section, and calculate the initial normal velocity of steam at the vapor-liquid interface. ; b) The boundary of the steam zone is obtained by solving the energy equation of the steam zone using the interface temperature of the liquid absorption core region and the steam zone and its corresponding saturation pressure as initial conditions; c) Calculate the initial conditions of the boundary pressure using the temperature distribution, solve the continuity equation and momentum equation of the steam region, and obtain the pressure and velocity distribution of the steam region; d) Repeat steps b)-c) until the temperature field converges.

[0080] In summary, compared with the prior art, this application has at least the following advantages and application effects: 1) Model innovation, practical application: This invention proposes for the first time a dedicated numerical model for "parallel" heat pipe structures, which solves the problem that existing single-pipe models cannot be applied to such complex structures and is more in line with the needs of practical application scenarios such as space stacks.

[0081] 2) High simulation accuracy: By introducing a multi-stage, multi-physics coupling simulation strategy, accurate simulation of the entire process from solid-state heating to continuous steam flow is achieved. In particular, the use of three-dimensional Navier-Stokes equations in the steam zone can realistically reproduce the secondary flow and radial parameter distribution generated at the bend, which is impossible to achieve with traditional one-dimensional or two-dimensional models.

[0082] 3) Advanced algorithms and stable solutions: A phase change processing model based on equivalent physical property parameters, a heat transfer approximation method for transition flow based on additional thermal conductivity, and a vapor-liquid interface coupling algorithm based on Newton's iteration method are proposed. These methods together ensure the numerical stability of the calculation process and the physical authenticity of the results.

[0083] 4) Strong engineering guidance value: This startup program can output the detailed spatiotemporal distribution of key parameters (temperature, pressure, flow rate) during the startup process, which can be used to predict heat pipe startup time, evaluate heat transfer limit, and optimize structural design, providing a powerful numerical simulation tool for the development of high-performance heat pipe reactors.

[0084] This application also provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the above-described method. This electronic device can be any smart terminal, including tablet computers, in-vehicle computers, etc.

[0085] It is understood that the content of the above method embodiments is applicable to this device embodiment. The specific functions implemented by this device embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0086] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method.

[0087] It is understood that the content of the above method embodiments is applicable to this storage medium embodiment. The specific functions implemented in this storage medium embodiment are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments.

[0088] Memory, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs and non-transitory computer-executable programs. Furthermore, memory may include high-speed random access memory, and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some embodiments, memory may optionally include memory remotely located relative to the processor, and these remote memories can be connected to the processor via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

[0089] This application also provides a computer program product, including a computer program that, when executed by a processor, implements the above-described method.

[0090] It is understood that the content of the above method embodiments is applicable to the embodiments of this program product. The specific functions implemented in the embodiments of this program product are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments. The executable computer program code or "code" used to perform the various embodiments can be written in high-level programming languages ​​such as C, C++, Python, Smalltalk, Java, JavaScript, Visual Basic, Structured Query Language (e.g., Transact-SQL), Perl, or in various other programming languages.

[0091] The embodiments described in this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided by the embodiments of this application. As those skilled in the art will know, with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0092] Those skilled in the art will understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of this application, and may include more or fewer steps than shown, or combine certain steps, or different steps.

[0093] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0094] Those skilled in the art will understand that all or some of the steps in the methods disclosed above, as well as the functional modules / units in the systems and devices, can be implemented as software, firmware, hardware, or suitable combinations thereof.

[0095] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0096] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0097] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of the units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0098] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0099] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0100] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes multiple instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this application. The aforementioned storage medium includes various media capable of storing programs, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0101] The preferred embodiments of the present application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the embodiments of the present application shall be within the scope of the claims of the present application.

Claims

1. A parallel high-temperature heat pipe structure model, characterized in that, It includes two straight pipes with identical structures and one bent pipe; The straight pipe, from radial to inner, includes a heat pipe outer wall, a liquid wick region, and a vapor region, and from axial to includes an evaporation section, an insulation section, and a condensation section connected in sequence. The bend connects the evaporation sections of the two straight pipes, forming a complete parallel loop; the radial structure of the bend is the same as that of the straight pipe.

2. The parallel high-temperature heat pipe structure model according to claim 1, characterized in that, The outer wall of the heat pipe is made of stainless steel, and the working fluid filled in the liquid wick area is liquid potassium metal.

3. The parallel high-temperature heat pipe structure model according to claim 1 or 2, characterized in that, The liquid-absorbing core area has a porous structure.

4. A numerical simulation method applied to the start-up process of a parallel high-temperature heat pipe structure model as described in any one of claims 1-3, characterized in that, Includes the following steps: Determine the geometric and physical property parameters of the parallel high-temperature heat pipe, establish a numerical model, and perform mesh generation and initialization; Heat flux density is applied to the outer wall of the evaporation section for heating. The unsteady heat conduction equation of the outer wall of the heat pipe and the liquid wick region is solved using a two-dimensional axisymmetric model to obtain the temperature distribution. When the working fluid in the wick region undergoes a phase change and generates steam, the axial heat transfer effect of the steam region is added to the heat conduction equation of the wick region in the form of an additional thermal conductivity coefficient for solving. The flow state of the steam zone is detected. When it is determined that the steam zone has established a completely continuous flow, the liquid core region and the steam zone are coupled and calculated at the vapor-liquid interface. Based on the coupling results, a three-dimensional numerical simulation of the steam working fluid flow and heat transfer in the steam zone is performed until the temperature field converges.

5. The method according to claim 4, characterized in that, When a solid-liquid phase change is detected in the working fluid within the wick region, the equivalent volumetric heat capacity and equivalent thermal conductivity of the wick region are calculated using an equivalent model. The equivalent model distinguishes the physical properties of the working fluid in three states—solid, molten, and liquid—based on temperature ranges, specifically as follows: when When using a solid working fluid, the calculation is performed. when When using a molten working fluid, the calculation is performed. when When using liquid working fluid, calculations are performed. in, The melting point temperature of the working fluid. This refers to the phase transition temperature range.

6. The numerical simulation method according to claim 4, characterized in that, The additional thermal conductivity The calculation formula is: in, The radius of the steam zone, The radius of the outer wall of the suction core. For latent heat of vaporization, The molecular mass of the working fluid. The dynamic viscosity of the working fluid. This is the universal gas constant. For steam pressure, For steam temperature, It is a Knudsen number.

7. The numerical simulation method according to claim 4, characterized in that, The coupling calculation of the liquid absorption core region and the vapor region at the vapor-liquid interface includes: Based on molecular dynamics theory, the net mass exchange rate of evaporation / condensation is calculated according to the pressure and temperature on both sides of the vapor-liquid interface. ; Based on the net mass exchange rate Calculate the thermal flow boundary conditions of the input steam region. ; Heat flow boundary conditions With the speed of sound limit of heat pipes Compare the values ​​and take the smaller value as the final heat flow boundary condition; Based on the final thermal flux boundary condition, calculate the initial normal phase velocity of steam at the vapor-liquid interface. , which serves as the entry boundary condition for three-dimensional numerical simulation.

8. The numerical simulation method according to claim 7, characterized in that, By establishing the mass conservation equation at the vapor-liquid interface and using Newton's iterative method to solve for the uniform temperature in the vapor zone, the uniform temperature of the vapor zone can be determined. Then, the net mass exchange rate is calculated. .

9. The numerical simulation method according to claim 4, characterized in that, The three-dimensional numerical simulation of the steam working fluid flow and heat transfer in the steam zone includes: Solve the three-dimensional steady-state governing equations for the vapor region, including the continuity equation, momentum equation, energy equation, ideal gas law, and Clausius-Clapeyron equation; wherein the momentum equation neglects the change of viscosity with position, and the energy equation considers the work done by pressure and viscous forces.

10. The numerical simulation method according to claim 9, characterized in that, The three-dimensional steady-state control equations are discretized and solved using the finite element method. The solution process includes: A1. Consistent temperature obtained using coupled calculations and initial normal velocity Initialize the steam zone; A2. Solve the energy equation for the steam region to obtain the temperature distribution of the steam region; A3. Using the temperature distribution, solve the continuity equation and momentum equation to obtain the pressure and velocity distribution in the steam zone; A4. Iterate through steps A2 and A3 until the temperature field converges.

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