| With subway line capacity increasing year by year,the overheating problems in the subway all over the world were continually revealed.In order to analyze the causes of overheating,and thus more targeted to improve the thermal environment inside the subway tunnel,it is necessary to analyze the air temperature change law of the long-term heat storage subway tunnels.Ventilation,as one of the most simple and convenient way to improve the thermal environment,first of all is considered for cooling in subway tunnels.In this paper,on the basis of the tunnel air temperature change law,the further study on the feasibility of mechanical ventilation cooling for subway tunnels is launched.First,taking the subway tunnel air temperature as the research object,according to the first law of thermodynamics,heat transfer knowledge,and the force-restore theory,the mechanical ventilation-soil heat coupling physical model and mathematical model are established under a year cycle.The subway tunnel air temperature prediction equation is obtained by solving the mathematical model.Four physical quantities,the time parameter of the system,the parameterized convective heat transfer coefficient of air and surrounding soil in the tunnel,the parameterized heat transfer coefficient between the soil of the heat storage layer and the soil of the thermostatic layer,the temperature rise caused by the internal heat source,with physical meaning were obtained by integrating the parameters in the equation.The law of the average tunnel air temperature,the amplitude and the phase changing with the various physical quantities was analysed.Then,the subway tunnel air temperatures of London,Harbin,Beijing,Guangzhou,Kunming were calculated by using the mechanical ventilation-soil heat storage coupling model under the year cycle.Putting the outdoor meteorological parameters into the model,the subway tunnel temperature change equations of operating under long-term mechanical ventilation were obtained.The comparative analysis on the influence of air temperature change in tunnels has been done among the different outdoor conditions,different air change rate and the different quantity of heat production.The change trend of the subway tunnel temperature and the main reasons of the temperature rise were obtained.Finally,in order to explain the causes of the tunnel overheating and the feasibility of ventilation cooling,the tunnel air temperature in the typical summer day was calculated separately.By establishing the mechanical ventilation-soil heat coupling mathematical model under a daily cycle,putting the typical summer day outdoor conditions of all the regions into the model,the tunnel air temperature of different regions is obtained.This paper defines three different types of subway tunnels,analyzes and obtains the overheating temperature limits of different types of subway tunnels,and then analyzes the feasibility of mechanical ventilation cooling for different types of subway tunnels.The main achievements of this paper are subway tunnel mechanical ventilation-soil heat coupled physical model,mathematical model and the temperature forecast equation of subway tunnel under the condition of long-term heat storage and full-time mechanical ventilation.It's obtained that the tunnel average air temperature is mainly related to air change rate,inner heat production,and amplitude is mainly related to the amplitude of the outdoor air temperature,air change rate,and the phase shift is only related to air change rate.Under the year cycle,the biggest phase shift between the tunnel air temperature and the outdoor temperature is 26 d,about 0.07 cycles.For the subway lines with the problem of tunnel overheating,the method of increasing the air change rate is limited to cool such subway lines.For future possible risk of overheating subway lines,when the air change rate increases from 5 times/h to 15 times/h,the subway tunnel temperature increment will reduce 2 ? after running for fifty years at the typical day in the summer. |
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