| With the rapid development of urban rail transit in China,the subway,as a green,energy-saving,safe and fast means of transportation,plays an important role in solving the traffic congestion problem.Due to its convenient,efficient and comfortable characteristics,the subway passenger traffic has increased year by year,resulting in shortened train interval and increased train running times,which inevitably causes the air quality in the subway station to drop,and harms to the health of passengers and subway workers.In this paper,the island platform of a subway screen door system is taken as the research object.The research method of CFD simulation is used to optimize the air volume control index from the traffic flow of the influencing factors of fresh air volume,the concentration of outdoor fresh air carbon dioxide and the departure interval.The research content of this paper is as follows:（1）Introduced the characteristics of subway underground environment and environmental control system;introduced the design standards of ventilation and air conditioning in public areas of metro stations in China;summarized the research status and achievements of air quality and fresh air volume control indicators in public areas of metro stations at home and abroad;The formulas for the number of waiting people on the subway station and the amount of fresh air are calculated.The load calculations are carried out during the off-peak and peak periods of the summer passenger flow;the evaluation criteria for the air quality of the subway platform are determined.（2）Using Airpak3.0,the physical model of the 1:1 platform of the sukbway screen door system and the 1:1 block model of the human body during peak and off-peak periods were established.The respirable particulate matter was established by Ansys Fluent 14.5.The DPM model is a simplified analysis of the PM2.5 force of the inhalable particulate matter.The gas-solid two-phase flow simulation method is briefly introduced and its mathematical theory model is given.（3）A comparative analysis of CO2 concentration,thermal comfort and PM2.5concentration of respirable particulate matter in the public areas of peak and off-peak subway stations.The influence law of passenger flow,outdoor fresh air carbon dioxide concentration and departure interval on the control index of fresh air volume in the public area of the subway platform is analyzed.（4）Simulating and comparing the carbon dioxide concentration distribution in the public areas of the subway stations under different passenger flow conditions and different departure intervals,and obtaining the peak and off-peak periods of the passenger flow matching the new air volume index of 12.6m3/h.The optimal starting interval is obtained.The simulation and comparative analysis of the carbon dioxide concentration distribution in eight different returning wind conditions and different horizontal heights are carried out,and the optimal return wind speed is obtained during peak and off-peak periods.The value of the new air volume control indicator is obtained.The main conclusions are as follows:（1）For the level of the breathing zone from 1.1 m to 1.5 m,the concentration of carbon dioxide in the public area of the passenger flow during the off-peak period is close to the concentration of carbon dioxide in the peak period of the passenger flow.For the Y=2.5 m and Y=3 m horizontal planes,the carbon dioxide concentration in the public area of the peak passenger flow stage is higher than that in the non-peak period.For the horizontal plane of 1.13 m,the mass fraction of PM2.5 is maintained at(1×10-66×10-6)kg/m3 during the peak period of passenger flow.The mass fraction of PM2.5during the off-peak phase of passenger flow is maintained at(1×10-63×10-6)kg/m3,and the PM2.5 concentration in the public area of the passenger flow peak is higher than the PM2.5 concentration in the off-peak period.As the level increases,the mass fraction of PM2.5 slowly decreases.The passengers in the non-peak period of passenger flow have a moderate heat perception.The percentage of people who are dissatisfied with the thermal environment is about 8.5%.The passengers at the peak of passenger flow have a moderate thermal sensation.The percentage of people in the respiratory area who are dissatisfied with the thermal environment is about 12.5%.Therefore,for the peak and off-peak period of the passenger flow of the island system of the screen door system,when the single fresh air volume index is 12.6m3/h,the carbon dioxide concentration and the PM2.5 concentration are not below the specification limit.The temperature field,velocity field and PMV-PPD basically meet the air quality requirements of the public area of the platform.（2）The concentration of outdoor fresh air carbon dioxide has a direct impact on the fresh air volume index.Under the premise of ensuring good outdoor winds,with the increase of the outdoor fresh air carbon dioxide concentration,the value of the fresh air volume index increases,and the new air volume consumed is also larger.（3）For the screen door system,the platform operation of the island platform is flat,the departure interval is about 5 minutes,and the single fresh air volume indicator is matched to 12.6 m3/h,which can ensure the air quality requirements of the public area of the platform and reduce the cost of subway operation.For the peak operation period of the island system platform of the screen door system,the departure interval is about 2.5min,which matches the single fresh air volume index of 12.6 m3/h.It can ensure the air quality of the public area of the platform and relieve the pressure of passenger flow.（4）For the screen door system,when the subway station operates in the peak period,the demand for fresh air volume is increasing as the air supply speed increases.When the air supply speed is 2 m/s,the required fresh air volume is calculated to be 10192 m3/h,and the recommended index for single-person calculation of fresh air volume is 20.4m3/h.For the peak period of subway operation of the island system of the screen door system,as the air supply speed increases,the demand for fresh air volume is also increasing.When the air supply speed is 3 m/s,the required fresh air volume is calculated to be 25350 m3/h,and the single-person calculation new air volume recommendation index is about 21 m3/h.Finally,combined with the departure interval and the return air speed,under the premise of satisfying the air quality in the public area of the platform,it is not recommended to use the single fresh air volume index of 12.6 m3/h.For the off-peak period of subway operation,the single-person calculation of fresh air volume index is recommended to be 20.4 m3/h.For the peak period of subway operation,the single-person calculation of fresh air volume index is recommended to take 21 m3/h. |
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