Design method for heat buffering and enhanced heat transfer of pipe wall of low-vacuum pipeline traffic system

Abstract

The invention relates to the technical field of low-vacuum pipeline traffic thermal protection and thermal management, in particular to a low-vacuum pipeline traffic system pipe wall thermal buffering and enhanced heat transfer design method which comprises the steps that geometric parameters of a low-vacuum pipeline traffic system are obtained, and a geometric model is constructed; determining operation parameters, structure parameters and external environment parameters of the low-vacuum pipeline traffic system; performing numerical simulation calculation on the basis of the geometric model, the operation parameters, the structure parameters and the outside-pipe environment parameters to obtain in-pipe aerodynamic thermal environment dynamic change characteristics; based on the dynamic change characteristics of the aerodynamic thermal environment, selecting or preparing a composite phase change material; and constructing a pipe wall model for coupling the composite phase change material and the heat pipe. Effective buffering of strong heat flow impact and rapid heat guiding-out are achieved, the temperature and thermal stress of the inner wall of the pipeline are reduced, and the thermal safety and operation reliability of a system are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of low-vacuum tube transportation heat protection and heat management, and particularly relates to a low-vacuum tube transportation system pipe wall heat buffering and heat transfer enhancement design method. BACKGROUND

[0002] The low-vacuum tube transportation system is a new type of rail transportation, which can run at a high speed or a super high speed by creating a low-vacuum environment on the ground. However, the high-speed train runs in a limited tube space, and inevitably faces severe aerodynamic problems. The aerodynamic heating caused by the strong compression and friction of the high-speed train and the air in the tube seriously threatens the train operation safety, the normal operation of the equipment in the tube and the safety of the tube structure.

[0003] When the train runs at a high speed in the tube, a large amount of aerodynamic heat is rapidly accumulated in the tube. The airflow in front of the train is compressed and the temperature is increased; the airflow behind the train is expanded and the temperature is decreased. With the continuous running of the train, a dynamic aerodynamic heat environment is formed in the tube. For a certain position of the tube, it will be swept by the high-temperature airflow and the low-temperature airflow, and at the junction of the two airflows, the tube will also experience a transient and sharp heat flow, which threatens the thermal safety of the tube structure. SUMMARY

[0004] In view of the deficiencies in the prior art, the purpose of the embodiments of the present application is to provide a low-vacuum tube transportation system pipe wall heat buffering and heat transfer enhancement design method, which combines the high thermal conductivity, high latent heat of the composite phase change material and the heat transfer enhancement characteristics of the heat pipe, stores the strong heat flow in front of the train, and discharges the condensed section of the heat pipe outside the tube or neutralizes it with the low-temperature airflow behind the train, so as to reduce the thermal shock and thermal stress of the inner wall of the tube.

[0005] In order to achieve the above-mentioned purpose, the embodiments of the present application provide the following technical solutions: A low-vacuum tube transportation system pipe wall heat buffering and heat transfer enhancement design method comprises the following steps: obtaining the geometric parameters of the low-vacuum tube transportation system, and constructing a geometric model; determining the operation parameters, structure parameters and tube external environment parameters of the low-vacuum tube transportation system; based on the geometric model, the operation parameters, the structure parameters and the tube external environment parameters, performing numerical simulation calculation to obtain the dynamic change characteristics of the aerodynamic heat environment in the tube; based on the dynamic change characteristics of the aerodynamic heat environment, selecting or preparing a composite phase change material; and constructing a pipe wall model coupled with the composite phase change material and the heat pipe.

[0006] Optionally, the geometric parameters include the train head length, the train middle length, the train tail length, the maximum train body radius, the tube inner wall radius, and the blockage ratio, wherein the blockage ratio is the ratio of the square of the maximum train body radius to the square of the tube inner wall radius.

[0007] Optionally, the geometric model is a two-dimensional axisymmetric structure, including a low-vacuum pipeline and a high-speed train, the low-vacuum pipeline is modeled as a long straight cylindrical structure, and the high-speed train is modeled as a two-dimensional axisymmetric structure including a train head, a train body and a train tail.

[0008] Optionally, the operation parameters include low-vacuum environment parameters and train operation parameters, the low-vacuum environment parameters include an initial pressure in the pipeline, a static temperature and an environmental sound velocity, and the train operation parameters include a train speed and a Mach number based on the static temperature and the environmental sound velocity.

[0009] Optionally, the structure parameters include train body structure parameters and pipeline structure parameters, the train body structure parameters include a train body outer surface radiation emissivity, and the pipeline structure parameters include a pipeline inner wall surface radiation emissivity, a pipeline thickness, a pipeline outer wall surface radiation emissivity and a pipeline heat generation rate.

[0010] Optionally, the pipeline outer environment parameters include a convection heat transfer coefficient between the pipeline outer wall surface and the pipeline outer environment, a pipeline outer environment temperature and a pipeline outer radiation temperature.

[0011] Optionally, the dynamic change characteristics of the aerodynamic heat environment mainly include temperature characteristics of the pipeline inner wall surface changing over time.

[0012] Optionally, the thermal conductivity and latent heat characteristics of the composite phase change material are higher than a set value, and the phase change temperature of the composite phase change material is selected based on the pipeline inner wall temperature and is lower than a pipeline inner wall thermal safety limit temperature.

[0013] Optionally, the heat pipe is a non-gravity heat pipe, which can adapt to a circular pipeline structure and work at any angle.

[0014] Optionally, in the pipeline wall model, the composite phase change material is located at the innermost layer of the pipeline wall, the heat pipe evaporation section is located at the composite phase change material, the heat pipe condensation section is located at the outermost layer of the pipeline wall, and the heat pipe adiabatic section is located at other structure layers of the pipeline wall.

[0015] The one or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages: The present application obtains the geometric parameters of the low-vacuum pipeline transportation system and constructs a geometric model to provide an accurate space basis for subsequent simulation. The operating parameters, structural parameters and external environmental parameters of the pipeline are determined to ensure that the numerical simulation calculation can reflect the thermal load conditions under actual working conditions. Based on these parameters, numerical simulation calculation is performed to obtain the dynamic variation characteristics of the aerodynamic thermal environment in the pipeline, thereby quantifying the transient behavior of the heat flow impact. Based on the dynamic variation characteristics, the composite phase change material is selected or prepared to match the material properties with the thermal environment. A pipeline wall model coupled with the composite phase change material and the heat pipe is constructed to realize active buffering and efficient heat transfer. The pipeline structure proposed by the method can to some extent cope with strong heat flow impact, the phase change layer absorbs heat and reduces the thermal stress of the inner wall structure of the pipeline, and at the same time, the heat is discharged outside the pipeline through the condenser section of the heat pipe or directly released to the low-temperature airflow behind the train through the phase change material for consumption, so as to reduce the thermal safety risk of the inner wall of the pipeline.

[0016] The advantages of the additional aspects of the present application will be given in the following description, some of which will become apparent from the following description, or will be understood through practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only show some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings. In addition, the sizes or distances between each other are exaggerated for showing the positions of the components, and the schematic diagram is only used for illustration.

[0018] Figure 1 is a flow chart of the design method provided by the embodiments of the present application; Figure 2 is a model schematic diagram of the low-vacuum pipeline transportation system provided by the embodiments of the present application; Figure 3 is a pipeline inner wall temperature distribution diagram under a certain representative working condition, i.e., a stable running moment, provided by the embodiments of the present application; Figure 4 is a pipeline wall model schematic diagram under the coupling of the phase change material and the heat pipe provided by the embodiments of the present application; DETAILED DESCRIPTION It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in the present application have the same meaning as generally understood by those skilled in the art to which the present application belongs. In addition, it should be understood that when the terms "comprise" and / or "include" are used in the present specification, they mean that the features, steps, operations, devices, components and / or their combinations are present.

[0019] Term explanation: The phase change material (PCM) is a substance that can change its physical state at a specific temperature and absorb, store or release a large amount of latent heat during this process, and the composite phase change material can use high latent heat PCM as the base material, add high thermal conductivity filler to build an efficient heat conduction path, and maintain the characteristics of high latent heat and high thermal conductivity.

[0020] The heat pipe is a passive heat transfer device that uses a phase change process to efficiently transfer heat. In the evaporation section of the heat pipe, the working fluid absorbs heat and evaporates, reaches the condensation section, releases latent heat and condenses, and then returns to the evaporation section by gravity or capillary structure. The heat pipe can achieve high temperature uniformity and heat conduction performance without energy consumption, and has the characteristics of low cost, high reliability, long service life, simple and diverse structure, etc.

[0021] As shown in Figure 1 The embodiment provides a low-vacuum tube transportation system pipe wall heat buffering and heat transfer enhancement design method, which comprises the following steps: obtaining geometric parameters of a low-vacuum tube transportation system and constructing a geometric model; determining operation parameters, structure parameters and pipe outer environment parameters of the low-vacuum tube transportation system; based on the geometric model, the operation parameters, the structure parameters and the pipe outer environment parameters, performing numerical simulation calculation to obtain dynamic change characteristics of a pipe internal aerodynamic thermal environment; based on the dynamic change characteristics of the aerodynamic thermal environment, selecting or preparing a composite phase change material; and constructing a pipe wall model coupled with the composite phase change material and a heat pipe.

[0022] By obtaining the geometric parameters of the low-vacuum tube transportation system and constructing the geometric model, the spatial structure characteristics of the system can be accurately restored, a basic framework is provided for subsequent numerical simulation calculation, and deviation of simulation results caused by inaccurate structure description is avoided. The operation parameters, the structure parameters and the pipe outer environment parameters are determined, so that internal and external influencing factors during system operation can be comprehensively covered, the numerical simulation calculation can be ensured to be consistent with the actual operation scene, and calculation errors caused by missing parameters are reduced. Based on the above-mentioned geometric model and various parameters, the numerical simulation calculation can accurately obtain the dynamic change characteristics of the pipe internal aerodynamic thermal environment, provide data basis for selection or preparation of the composite phase change material in the subsequent process, and avoid blindness in material selection. Based on the dynamic change characteristics of the aerodynamic thermal environment, the composite phase change material can be selected or prepared, so that the material performance can be matched with the pipe internal thermal environment, and the material can play an effective role. The pipe wall model coupled with the composite phase change material and the heat pipe is constructed, the high thermal conductivity and high latent heat characteristics of the composite phase change material are used to absorb heat in the pipe, the thermal stress of the pipe inner wall is reduced, heat is transferred to the outside of the pipe by the high-efficiency heat transfer characteristics of the heat pipe, the problems of low pipe heat conduction efficiency, lack of heat buffering capacity and poor heat dissipation effect are solved, the safety of the pipe structure and train operation is ensured, and equipment failure caused by high temperature in the pipe can also be avoided.

[0023] The geometric parameters include the length of the train head, the length of the train middle, the length of the train tail, the maximum radius of the train body, the radius of the inner wall of the pipe, and the blockage ratio, which is the ratio of the square of the maximum radius of the train body to the square of the inner wall radius of the pipe.

[0024] Obtaining the train's head length, middle length, tail length, and maximum radius of the vehicle body accurately describes the train's external dimensions. The inner wall radius of the pipe clarifies the pipe's spatial size. These parameters collectively determine the relative positional relationship and spatial clearance between the train and the pipe, providing a foundation for subsequent analysis of the interaction between the train and the air inside the pipe during operation. The blockage ratio is calculated by dividing the square of the train's maximum radius of the vehicle body by the square of the inner wall radius of the pipe. This parameter reflects the proportion of space occupied by the train within the pipe. Different blockage ratios result in variations in the airflow state and aerodynamic heat generation within the pipe during train operation. Accurately obtaining the blockage ratio improves the accuracy of numerical simulations of the aerodynamic thermal environment within the pipe, thereby providing a more precise basis for the selection of composite phase change materials and contributing to improved thermal protection of the subsequent pipe wall model.

[0025] like Figure 2 As shown, the geometric model is a two-dimensional axisymmetric structure, including a low-vacuum pipe and a high-speed train. The low-vacuum pipe is modeled as a long straight cylindrical structure, and the high-speed train is modeled as a two-dimensional axisymmetric structure including the front, middle and rear of the train.

[0026] The geometric model employs a two-dimensional axisymmetric structure, which significantly reduces the workload and computation time of numerical simulation while ensuring computational accuracy, thereby improving design efficiency. Modeling the low-vacuum pipe as a long, straight cylindrical structure accurately reflects the axial consistency of the pipe, facilitating the analysis of thermal environment changes at various locations within the pipe. The high-speed train is modeled as a two-dimensional axisymmetric structure including the front, middle, and rear sections, precisely reflecting the shape differences of different parts of the train. Since different parts of the train interact differently with the air inside the pipe during operation, resulting in varying aerodynamic heat distributions, this modeling method improves the accuracy of simulating the generation and distribution of aerodynamic heat around the train. This leads to more realistic dynamic changes in the aerodynamic environment, providing a reliable basis for the selection of composite phase change materials and the construction of pipe wall models.

[0027] The operating parameters include low vacuum environment parameters and train operating parameters. The low vacuum environment parameters include the initial pressure inside the tube, static temperature, and ambient sound speed. The train operating parameters include the train speed and the Mach number based on the static temperature and ambient sound speed.

[0028] The initial pressure and static temperature in the tube are the core parameters to describe the low vacuum environment in the tube. Different initial pressure and static temperature will affect the density and thermodynamic properties of the air in the tube, and further affect the amount of aerodynamic heat generated and the transfer characteristics when the train is running. The environmental sound speed is related to the static temperature in the tube, and is a key parameter for calculating the Mach number. The train speed directly determines the relative motion speed of the train and the air in the tube. The higher the speed, the greater the amount of aerodynamic heat generated. The Mach number is calculated by the ratio of train speed to environmental sound speed, which can reflect the level of train running speed relative to sound speed, and is an important basis for judging the state of airflow in the tube. The state of airflow will significantly affect the distribution and intensity of aerodynamic heat. Accurate determination of these operating parameters can enable numerical simulation calculation to accurately simulate the aerodynamic heat environment in the tube under different operating conditions, ensure that the dynamic change characteristics of the thermal environment obtained are consistent with the actual running scene, provide a basis that meets the actual needs for subsequent selection of composite phase change material and construction of tube wall model, and ensure that the tube wall model can effectively play the role of heat buffering and heat transfer enhancement under different operating conditions.

[0029] The structure parameters include a car body structure parameter and a pipeline structure parameter, the car body structure parameter includes a car body outer surface radiation emissivity, and the pipeline structure parameter includes a pipeline inner wall surface radiation emissivity, a pipeline thickness, a pipeline outer wall surface radiation emissivity, and a pipeline heat generation rate.

[0030] The car body outer surface radiation emissivity reflects the ability of the train outer surface to radiate heat outward, and this parameter will affect the radiation heat exchange process between the train and the pipeline, and further affect the distribution of aerodynamic heat in the tube and the temperature change of the pipeline inner wall. The pipeline inner wall surface radiation emissivity determines the characteristics of the pipeline inner wall in absorbing and radiating heat, and together with the car body outer surface radiation emissivity, it affects the radiation heat exchange efficiency between the train and the pipeline inner wall. The pipeline thickness is related to the structural strength and heat conduction performance of the pipeline. The heat conduction capacity and the ability to withstand thermal stress of the pipeline will be different with different thicknesses. The pipeline outer wall surface radiation emissivity affects the heat dissipation effect of the pipeline outer wall to the environment outside the pipeline. The pipeline heat generation rate includes the heat generated by the pipeline itself due to material characteristics or external environment. This parameter will increase the heat load of the pipeline. If it is ignored, it will cause the predicted temperature of the pipeline inner wall in the numerical simulation calculation to be lower, and affect the accuracy of the selection of the composite phase change material. Accurate determination of these structure parameters can enable the numerical simulation calculation to comprehensively consider the factors such as radiation heat exchange, pipeline self-heat conduction and heat generation, improve the accuracy of the simulation of the aerodynamic heat environment in the tube, and ensure that the subsequently selected composite phase change material and constructed tube wall model can adapt to the structural characteristics of the pipeline, effectively cope with the heat load of the pipeline, and ensure the safety of the pipeline structure.

[0031] The pipeline outer environment parameters include a convection heat transfer coefficient of the pipeline outer wall surface and the environment outside the pipeline, an environment temperature outside the pipeline, and an outer radiation temperature of the pipeline.

[0032] The convection heat transfer coefficient of the outer wall surface of the pipeline and the external environment of the pipeline reflects the ability of the outer wall of the pipeline to transfer heat to the external environment of the pipeline by convection. The greater the coefficient, the better the effect of convective heat dissipation. The external environment temperature of the pipeline is the target environment temperature of the outer wall of the pipeline. The lower the external environment temperature of the pipeline, the greater the temperature difference between the outer wall of the pipeline and the environment, and the more conducive to heat dissipation. The external radiation temperature of the pipeline is the temperature of the external environment of the pipeline to the outer wall of the pipeline. This parameter will affect the radiation heat transfer process of the outer wall of the pipeline. If the external radiation temperature of the pipeline is high, it will reduce the heat radiated by the outer wall of the pipeline, and reduce the heat dissipation effect. Accurate determination of these external environment parameters of the pipeline can comprehensively consider the heat transfer process between the outer wall of the pipeline and the external environment of the pipeline, accurately predict the temperature change of the inner wall of the pipeline, avoid inaccurate judgment of the thermal load of the pipeline due to the neglect of the external environment factors of the pipeline, and then ensure that the subsequent selection of the composite phase change material and the construction of the pipeline wall model can adapt to the external environment conditions of the pipeline, effectively transfer the heat in the pipeline to the outside of the pipeline, and ensure the thermal safety of the pipeline.

[0033] As shown in Figure 3 The dynamic change characteristics of the aerodynamic thermal environment mainly include the temperature characteristics of the inner wall of the pipeline changing with time.

[0034] The temperature characteristics of the inner wall of the pipeline changing with time can reflect the position of the high-temperature region and the low-temperature region in the pipeline, directly reflect the thermal load state of the inner wall of the pipeline, and can clearly determine the temperature level of the inner wall of the pipeline at different time points and whether there is an instantaneous sharp change of heat flow. Obtaining these dynamic change characteristics can provide a direct basis for the selection of the composite phase change material, such as determining the phase change temperature of the composite phase change material to be lower than the temperature of the high-temperature region of the pipeline, and determining the thermal response speed of the material according to the heat flow change rate; at the same time, it also provides a direction for the construction of the pipeline wall model, which can determine the arrangement density of the heat pipe according to the temperature intensity of the high-temperature region, and effectively realize heat buffering and heat transfer enhancement.

[0035] The thermal conductivity and latent heat characteristics of the composite phase change material are higher than the set value, and the phase change temperature of the composite phase change material is selected based on the temperature of the inner wall of the pipeline and is lower than the thermal safety limit temperature of the inner wall of the pipeline.

[0036] The composite phase change material exhibits a higher thermal conductivity than a set value, ensuring rapid absorption of heat transferred from the pipe's inner wall and preventing heat buildup that could lead to a rapid temperature increase. Its latent heat characteristic is also higher than a set value, allowing the material to absorb a significant amount of heat during phase change, enhancing its thermal buffering capacity, effectively reducing temperature fluctuations on the pipe's inner wall, and alleviating thermal stress. The phase change temperature of the composite phase change material is selected based on the pipe's inner wall temperature, ensuring that the material undergoes phase change when the pipe's inner wall temperature reaches the required thermal buffering level, thus providing timely protection. Furthermore, the phase change temperature is below the pipe's inner wall's thermal safety limit, ensuring that the pipe's inner wall temperature does not exceed the safety threshold and preventing structural damage due to high temperatures. These characteristics enable the composite phase change material to specifically address the thermal environment inside the pipe, effectively absorbing heat, buffering thermal shocks, and providing reliable thermal protection for the pipe's inner wall. It also lays the foundation for subsequent coupling with a heat pipe, ensuring that heat is effectively absorbed before being transferred out through the heat pipe.

[0037] The heat pipe is a non-gravity heat pipe, which can adapt to a circular pipe structure and operate at any angle.

[0038] The heat pipe employs a non-gravity design, eliminating the need for gravity-based recirculation of the working fluid. This allows it to adapt to varying installation angles within low-vacuum pipeline transportation systems, ensuring normal operation in diverse pipeline layouts and expanding the applicability of the pipe wall model. The heat pipe can accommodate circular pipe structures, matching common low-vacuum pipeline configurations, facilitating integration into the pipe wall model and ensuring a close fit between the heat pipe and the pipeline, thus improving heat transfer efficiency. The heat pipe can operate at any angle, further guaranteeing its normal operation in complex pipeline sections such as bends and inclines. This prevents heat pipe failure due to changes in pipeline angle, ensuring the pipe wall model continuously enhances heat transfer throughout the entire pipeline system, efficiently transferring the heat absorbed by the composite phase change material to the outside of the pipe and preventing heat accumulation inside the pipeline.

[0039] like Figure 4 As shown, the composite phase change material is located in the innermost layer of the pipe wall, the heat pipe evaporation section is located at the composite phase change material, the heat pipe condensation section is located in the outermost layer of the pipe wall, and the heat pipe insulation section is located in other structural layers of the pipe wall.

[0040] The composite phase change material is located at the innermost layer of the pipe wall and can directly contact the inner wall of the pipe. When the temperature of the inner wall of the pipe rises, the material can absorb heat in the first time, quickly play a heat buffer role, reduce the heat transfer to the internal structure of the pipe, and reduce the thermal stress of the pipe structure. The evaporation section of the heat pipe is located at the composite phase change material, which can directly contact and absorb the heat stored in the composite phase change material, improve the efficiency of heat transfer from the material to the heat pipe, avoid the heat accumulation in the material, and affect the heat buffer effect. The condensation section of the heat pipe is located at the outermost layer of the pipe wall, which can directly contact the external environment, facilitate the rapid heat transfer to the outside of the pipe, shorten the heat transfer path, and reduce the heat loss in the heat transfer process. The adiabatic section of the heat pipe is located in other structural layers of the pipe wall, which can reduce the heat loss of the heat pipe in the non-evaporation section and the non-condensation section, ensure that the heat is mainly absorbed in the evaporation section and released in the condensation section, and improve the heat transfer efficiency of the heat pipe. This arrangement forms an efficient heat transfer path between the composite phase change material and the heat pipe in the pipe wall, realizes the complete process from heat absorption in the inner wall of the pipe to heat release outside the pipe, and ensures the heat buffer and heat transfer enhancement effect of the pipe wall model.

[0041] Specific process: S1, obtain the geometric parameters of the low-vacuum tube transportation system, and construct a geometric model, as shown in Figure 2 , specifically as follows: The low-vacuum tube transportation system includes a low-vacuum tube and a high-speed train. The low-vacuum tube is a long straight cylindrical structure with an inner wall radius of , and the train runs at high speed on the center line of the low-vacuum tube. The high-speed train is a two-dimensional axisymmetric structure, including a head, a middle, and a tail, with a total length of L , a head length of , a middle length of , and a tail length of , wherein , ; the maximum radius of the train body is , ; and the blockage ratio is defined as: .

[0042] Construct a geometric model: the low-vacuum tube is modeled as a long straight cylindrical structure with an inner wall radius of , and the pipe wall thickness is t , wherein the pipe wall thickness is imaginary and does not need to be actually modeled; the high-speed train is modeled as a two-dimensional axisymmetric structure, which includes a head, a middle, and a tail, and does not consider the thickness of the train body.

[0043] S2, determine the operating parameters, structural parameters, and external environment parameters of the low-vacuum tube transportation system, specifically as follows: Operating parameters include low-vacuum environment parameters and train operating parameters. Low-vacuum environment parameters include the initial pressure inside the pipe. p 0 ( p 0 < 1 atm), static temperature T 0 and the corresponding ambient sound speed a 0. Train operating parameters include train speed. U 0 and the corresponding Mach number at static temperature M 0 =U 0 / a 0; Structural parameters include vehicle body structural parameters and piping structural parameters. Vehicle body structural parameters include the emissivity of the vehicle's outer surface. Pipeline structural parameters include the emissivity of the inner wall surface of the pipeline. Pipe thickness t ( t < ), the radiation emissivity of the outer wall of the pipe Pipeline heat production rate The pipeline material is pressure-bearing steel such as Q345R. The pipeline thickness should be calculated according to the relevant pressure-bearing standards. The solar radiation absorbed by the pipeline in the atmospheric environment can be converted into the pipeline heat generation rate and substituted into the calculation.

[0044] External environmental parameters include the convective heat transfer coefficient between the pipe's outer wall and the external environment. External ambient temperature External radiation temperature The convective heat transfer coefficient needs to be calculated with reference to the convective heat transfer formula when air is blown horizontally or vertically through the pipe. The external radiation temperature refers to the long-wave radiation from the external environment to the outer wall of the pipe, such as the atmosphere and the ground surface.

[0045] S3. Using the geometric model from step 1 and the parameters determined in step 2, numerical simulation calculations are performed to obtain the dynamic changes in the aerodynamic thermal environment inside the pipe, mainly the temperature characteristics of the inner wall of the pipe over time, as follows: CFD simulation tools can include Fluent, Star-CCM+, OpenFOAM, or other CFD simulation tools for transient calculations. The parameters input during simulation include: the selection of turbulence and radiation models, air properties, boundary conditions, transient calculation parameters, etc. The simulation process uses conventional techniques and will not be detailed here.

[0046] Once the train body surface temperature stabilizes and the calculation results meet the convergence criteria, the dynamic temperature change of the pipe inner wall is collected. At a train speed of 0.8 Ma, a blockage ratio of 0.1225, and an initial pipe pressure of 0.01 atm, after stable operation, as follows... Figure 3As shown, the temperature of the pipe wall in front of the train exceeds 40℃, the temperature of the pipe wall behind the train is about -10℃, and the temperature gradient of the pipe wall reaches 50℃.

[0047] S4, selecting or preparing a suitable composite phase change material according to the dynamic temperature characteristics obtained in step 3, as follows: The suitable composite phase change material needs to have the characteristics of high thermal conductivity (> 5 W / (m·K)) and high latent heat (> 250 kJ / kg), and can quickly respond to the phase change process in seconds to absorb a large amount of heat; The phase change temperature of the phase change material needs to be selected in combination with the pipe inner wall temperature under various operating conditions. Figure 3 For example, under this operating condition, the pipe wall temperature in the high temperature zone in front of the train is basically above 40℃, so the phase change temperature of the phase change material is preferably not lower than 40℃, and needs to be lower than the thermal safety limit temperature of the pipe inner wall structure. The thermal safety limit temperature of steel needs to be referred to relevant standards. In the high temperature zone in front of the train, the phase change material enters the heat absorption process, and part of the absorbed heat is neutralized in the low temperature zone behind the train, thereby reducing the pipe wall temperature gradient and reducing the structural thermal safety risk.

[0048] S5, constructing a pipe wall model coupling the phase change material and the heat pipe according to the phase change material determined in step 4, as shown in Figure 4 As shown, the specific steps are as follows: The selected heat pipe needs to be a non-gravity type, simple and various heat pipe, which can adapt to circular pipes and can work normally at any angle; The phase change layer where the composite phase change material is located is the innermost layer of the pipe wall (i.e. the pipe inner wall surface), the heat pipe evaporation section is at the phase change layer, the heat pipe condensation section is located at the outermost layer of the pipe wall (i.e. the pipe outer wall surface), and the heat pipe insulation section is located at other structural layers of the pipe wall; Part of the heat stored by the phase change material is transferred to the outside of the pipe through the heat pipe for release, and part of the heat is released to the low temperature airflow behind the train through the phase change process.

[0049] Although the specific embodiments of the present application are described above in combination with the drawings, it is not a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications or changes made by those skilled in the art on the basis of the technical solutions of the present application without creative labor are still within the protection scope of the present application.

Claims

1. A method for low vacuum tube transportation system pipe wall thermal buffering and enhanced heat transfer design, characterized in that, The application relates to a method for designing a low-vacuum tube transportation system. The method comprises the following steps: acquiring geometric parameters of the low-vacuum tube transportation system and constructing a geometric model; determining operation parameters, structure parameters and tube-outside environment parameters of the low-vacuum tube transportation system; based on the geometric model, the operation parameters, the structure parameters and the tube-outside environment parameters, performing numerical simulation calculation to obtain dynamic variation characteristics of a tube-inside aerodynamic thermal environment; based on the dynamic variation characteristics of the aerodynamic thermal environment, selecting or preparing a composite phase change material; 2. The low vacuum tube transportation system pipe wall thermal buffer and enhanced heat transfer design method of claim 1, wherein, constructing a tube wall model coupling the composite phase change material and a heat pipe.

3. The low vacuum tube transportation system pipe wall thermal buffer and enhanced heat transfer design method of claim 1, wherein, The geometric parameters include a train head length, a train middle length, a train tail length, a train body maximum radius, a tube inside wall radius and a blockage ratio, wherein the blockage ratio is a ratio of the square of the train body maximum radius to the square of the tube inside wall radius.

4. The low vacuum tube transportation system pipe wall thermal buffer and enhanced heat transfer design method of claim 1, wherein, The geometric model is a two-dimensional axisymmetric structure, which comprises a low-vacuum tube and a high-speed train, wherein the low-vacuum tube is modeled as a long straight cylindrical structure, and the high-speed train is modeled as a two-dimensional axisymmetric structure comprising a train head, a train middle and a train tail.

5. The low vacuum tube transportation system pipe wall thermal buffer and enhanced heat transfer design method of claim 1, wherein, The operation parameters include low-vacuum environment parameters and train operation parameters, wherein the low-vacuum environment parameters include a tube-inside initial pressure, a static temperature and an environmental sound velocity, and the train operation parameters include a train speed and a Mach number based on the static temperature and the environmental sound velocity.

6. The low vacuum tube transportation system pipe wall thermal buffer and enhanced heat transfer design method of claim 1, wherein, The structure parameters include train body structure parameters and tube structure parameters, wherein the train body structure parameters include a train body outside surface radiation emissivity, and the tube structure parameters include a tube inside wall surface radiation emissivity, a tube thickness, a tube outside wall surface radiation emissivity and a tube heat generation rate.

7. The low vacuum tube transportation system pipe wall thermal buffer and enhanced heat transfer design method of claim 1 wherein, The tube-outside environment parameters include a tube outside wall surface and tube-outside environment convection heat transfer coefficient, a tube-outside environment temperature and a tube-outside radiation temperature.

8. The low vacuum tube transportation system pipe wall thermal buffer and enhanced heat transfer design method of claim 1, wherein, The dynamic variation characteristics of the aerodynamic thermal environment include a temperature characteristic of the tube inside wall surface changing with time.

9. The low vacuum tube transportation system pipe wall thermal buffer and enhanced heat transfer design method of claim 1 wherein, The composite phase change material has a heat conductivity and latent heat characteristic higher than a set value, and a phase change temperature of the composite phase change material is selected based on a tube inside wall temperature and is lower than a tube inside wall thermal safety limit temperature.

10. The low vacuum tube transportation system pipe wall thermal buffer and enhanced heat transfer design method of claim 1 wherein, The heat pipe is a non-gravity type heat pipe, which can adapt to a circular tube structure and work at any angle. In the tube wall model, the composite phase change material is located at an innermost layer of the tube wall, an evaporation section of the heat pipe is located at the composite phase change material, a condensation section of the heat pipe is located at an outermost layer of the tube wall, and an adiabatic section of the heat pipe is located at other structure layers of the tube wall.

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