Thermal Environment Characteristics And Changing Laws Of Different Standing Density In Subway Cars

With the rapid development of our country’s economy,the continuous improvement of residents’living standards,the increasing pressure of urban traffic,the convenience and comfort of passenger travel are becoming increasingly important.Based on this status quo,all large and medium-sized cities across the country are vigorously developing environmental-friendly,large-capacity,high-speed urban rail transit,but its construction and operating costs are high,and it has not been fully extended to towns and villages.As far as the riding environment is concerned,the thermal comfort and health requirements of the human body in subway cars are becoming stricter,and the fluctuation of passenger flow greatly affects the cold and heat loads of the subway air-conditioning system.Therefore,the problem how to integrate passenger flow into the thermal environment of the subway needs to be solved urgently.In order to ensure a better match between the predictable passenger flow and the comfort design of the subway,the Changsha B-type subway was used as the research object.In view of the climate characteristics of Changsha in cold winter and hot summer,the predictability of subway passenger flow fluctuations.Establish a physical model by replacing the original fully-loaded passenger conditions with the density of passenger seats and accurate standing-seat ratio,using RNG k-εturbulence model,and the software solver Airpak was used to study the thermal environment characteristics of the passenger compartment and the influence of different standing density on it during summer operation.Select continuous stations in Changsha Subway Line 2 for real-time passenger flow data collection and environmental parameter data collection to verify the effectiveness of the model.The research results show that the fluctuation of passenger flow continues to destroy the uniformity set by the designer,the velocity field,temperature field and pollutant CO₂concentration field deviate from comfort as the change of personnel,showing the flow field is unevenly distributed,and there is a high air velocity band at a height of 1.8m from the ground;the heat and metabolite CO₂emitted by passengers cannot be discharged in time due to the low air velocity in the lower part of the compartment,and there is a phenomenon of accumulation;There is a partial cold area at the opening and closing door,-2≤PMV≤-1,and a partial hot area near the air return,2.3≤PMV≤3,which is the position with the worst thermal comfort.In particular,when the standing seat density is greater than 4 persons/m~2,the air velocity at the head height of standing passengers v≥0.5m/s,if the number of passengers continues to increase,the low air velocity in the middle and lower compartments will be aggravated;when the standing seat density is greater than 5 persons/m~2,due to the thermal buoyancy in the middle of the compartment,the heat accumulation area gradually moved up to the passenger’s chest,and the temperature increase reached 3.5℃;when the seat density increased to 5 persons/m~2,the CO₂ concentration area is no longer elliptical,but with obvious partition boundaries,if the passenger flow continues to increase,the CO₂ volume fraction concentration value will exceed 0.15%,and passengers generally feel uncomfortable;when the seat density is less than 3 persons/m~2,-1≤PMV≤0,the passengers have a cold feeling,when the seat density is greater than 6 persons/m~2,1≤PMV≤3,the passengers generally have a sense of heat and the perception of standing passengers both are more than seated passengers.