Study On Heat Transfer Performance Of Maglev Train Body In Low Vacuum Pipeline

As a new type of transportation system,low vacuum pipeline transportation system is one of the most promising and disruptive transportation technologies.When the train runs at ultra-high speed in the low vacuum pipeline,the train will rub with the thin air in the pipeline,resulting in a rapid rise in the temperature of the body surface,which will have a negative impact on the safe operation of the vacuum pipeline traffic.Therefore,combining with the specific design characteristics of the low vacuum pipeline maglev train,this paper analyzes the heat transfer of the system,and studies its heat transfer characteristics and thermal insulation performance of the train body.Based on the FLUENT,the physical model in low vacuum pipeline transportation system is established under the condition of three-dimensional compressibility.The paper explores the high speed train running at different speeds under the initial conditions of different vacuum degree in the pipeline with the blocking ratio of 0.21,and simulates the temperature distribution of the low vacuum pipeline traffic system and the change rule of the maximum temperature of the train surface.Then,the heat transfer model of each part of the train body is established and the numerical simulation is carried out.Finally,combined with the influence of the typical thermal bridge structure of the train body,the heat transfer coefficient of the train body was optimized and analyzed by the weighted average method when the train was running at high speed in the low vacuum pipeline.And draw the following conclusions:(1)When a low vacuum pipeline maglev train runs at a certain speed in a pipeline with a blocking ratio of 0.21,the variation of the maximum temperature on the train surface with the degree of vacuum is relatively small.At the same time,with the same pressure in the pipe,the maximum temperature on the train surface increases with the increase of operating speed.In the relevant working conditions set in this article,when the train speed is less than 720km/h,the maximum temperature on the train surface decreases with the increase of vacuum,indicating that the aerodynamic heat generation effect is relatively strong when the train is running at a lower speed.When the train speed is greater than 900 km/h,the surface temperature of the train increases with the increase of vacuum.This indicates that the convective heat transfer effect is relatively strong when the train is running at a higher speed.It is shown that the interaction between aerodynamic heat and convective heat transfer affects the heat transfer process under low vacuum conditions.(2)When the blocking ratio of the magnetic suspension system in the low vacuum pipeline and the running speed of the train are constant,the heat transfer coefficient of the train body decreases with the increase of the vacuum degree in the pipeline.When the blocking ratio and vacuum degree of the low vacuum pipeline maglev system are fixed,the heat transfer coefficient of the train body increases with the increase of the train speed.According to the working conditions set in this paper,when the high-speed train runs under the working conditions of 0.01 pipeline vacuum and 500 km/h train speed,the heat transfer coefficient of the car body is the minimum.(3)The heat transfer coefficient of train body is 0.355W/(m~2·K)without considering the influence of thermal bridge,and 0.439W/(m~2·K)with an increase of 8.4%after considering the influence of thermal bridge.The results show that the thermal bridge will have a certain impact on the heat transfer performance of train body.According to the current comprehensive heat transfer coefficient of high-speed train body basically approaches0.917W/(m~2·K),which is larger than the numerical simulation results of 0.439W/(m~2·K)in this paper,it indicates that high-speed train will require higher heat insulation performance when running at high speed in low vacuum environment.