| Due to the low utilization of geothermal energy by the tunnel wind heat exchange system,this paper applies gravity heat pipes to the tunnel wind system to enhance the tunnel's heating capacity and heat transfer efficiency for outdoor fresh air in Shenyang in winter.The heat transfer performance of the traditional tunnel wind system is affected by the soil's thermal properties,the parameters of the inner wall surface of the pipe,the flow velocity in the tunnel and the geometry.And after the tunnel wind system has been running for too long,the cold accumulation on the inner surface of the site is more serious,which affects the heat transfer capacity of the soil and weakens the tunnel wind system's ability to warm up the outdoor fresh air.Firstly,the theoretical analysis method was used to study the heat transfer performance of the soil surface layer and the soil,and the change law of the temperature wave inside the soil layer was summarized.The heat exchange model of the underground wind system and outdoor fresh air was determined.Using the Ansys Fluent numerical simulation software,the temperature rise of the outdoor fresh air during the operation of the underground wind system at a certain length and different wind speeds in different times was calculated.Set the length of the tunnel to be 30 m,50m,and 70 m,the buried depth at the center of the tunnel is 6 m,and the wind speed is selected to be 0.5m/s,1m/s,1.5m/s,2m/s,2.5m/s and 3m/s,the running time is 2 hours,4 hours,6 hours,8 hours,10 hours,12 hours.After analyzing the heat exchange of the tunnel air system,the temperature rise of the fresh air in the tunnel and the cold accumulation of the soil on the surface of the tunnel.The conclusions drawn are: the higher the wind speed of the tunnel wind heat exchange system,the greater the total heat exchange between the soil and the air in the tunnel,the lower the temperature of the air at the tunnel outlet,the more serious the cold accumulation of soil;the operating wind speed is 0.5m The / s tunnel air system has the best heat exchange effect,which is also conducive to the continuous operation of the tunnel system for a long time,but the small air volume is not conducive to the small total heat exchange volume,so the inlet wind speed of 1m / s is more suitable.The continuous operation time of the tunnel wind heat exchange system should not exceed 6 hours.After 6 hours,the temperature of the soil around the tunnel drops quickly,and the phenomenon of cold accumulation is more obvious.Then,the gravity heat pipe was arranged in the tunnel wind system,and the phase change and temperature change of the working medium in the heat pipe were analyzed.The arrangement is 5 rows and 6 columns,a total of 30 gravity heat pipes,14 m away from the entrance of the tunnel.position.The conclusion is that when operating at a wind speed of1m/s,the heat exchange efficiency of the 30-meter heat pipe-underground wind system can reach 31.6%,which can be increased by 26.9% relative to the underground wind system,and the air at 24.64 m The average temperature is the same as the average temperature at the exit of the tunnel wind system,indicating that the use of heat pipes can reduce the length of thetunnel and reduce the initial investment of the tunnel wind system.Increasing the length of the condensation section and the evaporation section of the heat pipe in the tunnel can improve the heat transfer efficiency of the heat pipe-tunnel wind system and slow down the cold accumulation of soil near the tunnel.Due to the technology and its own research capacity,the working conditions of the heat pipe-underground wind system are less.It is suggested that future researchers should study the arrangement,location and number of heat pipes.The heat exchange potential of the heat pipe-underground wind system is great,which will have an important impact on the improvement of the heat exchange efficiency of the underground wind system and the use of geothermal energy. |
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