Research On Airflow Distribution Characteristics And Environment Comfort In Railway Passenger Car

Railway passenger car is one of the main vehicles in middle and long distance transportation in our country. The problem of comfort and air quality in the compartment induced by the good sealing is increasingly outstanding, which become the focus of attention and study by domestic and foreign scholars. The peculiarity in railway passenger car is that the heat flux and humidity internal and external has a big interference on thermal environment, and varies with different driving period and location, so the thermal environment in the compartment has a significant instability. Some relative studies on air organization and thermal comfort only in idle condition in train compartment have been carried out, but the airflow distribution characteristics and influencing factor are devoid of systematical and comprehensive research in our country. In this paper, aiming at the complexity of heat flux and contaminant source with multi-coupling in the 25K railway passenger car, the air distribution in the compartment is numerically simulated, and the thermal comfort and air quality is studied based on the anterior simulation result.The three-dimensional incompressible Reynolds time-average N-S equation is used to descript the air distribution. In the standard k-εturbulence model, the passenger body is regarded as contaminant and heat source, considering solar radiation and heat transfer of the compartment, and the calculation code is wholly compiled by the author successfully. The airflow and temperature distribution characteristics are studied in different conditions. The influence of body heat on turbulence airflow, temperature and CO2 concentration fields are analyzed, and the influence of supply air mode and air velocity on the air distribution parameters is discussed. The experimental measurement is carried out in the 25K railway passenger car. The data of experimental measurement are coinciding with the simulation results, which verify the reliability of the calculation code. Based on the state of uneven distribution of airflow and great difference of thermal sensation in the compartment, PMV and PD are successfully applied in the research of body thermal comfort. The influences of supply air velocity, temperature and supply air mode on thermal comfort are respectively studied. The results reveal that sew supply air at two sides of the ceiling is suitable for hard-seat car, and the supply air velocity should not be too large, because too large velocity easily produce local blowing feeling at the aisle while improving thermal comfort near the windows. Sew supply air mode is suitable for hard-berth sleeper to maintain the passengers'comfort, and the outlet should be located on the ceiling at the centre of the berth.On the basis of comprehensively considering thermal comfort and air quality,the index of AQI is first put forward to overall evaluate the air quality in the compartment. A conclusion that the optimal sew supply air velocity at two sides is 2.5m/s in hard-seat car is drawn. Supply air mode in hard-berth sleeper is improved, and the optimal supply air mode and supply air parameter simultaneously meeting the requirement of thermal comfort and good air quality are obtained. In hard-berth sleeper, the optimal supply air velocity is 2.5m/s with sew supply air. The research conclusion has an important reference value to guide the design of ventilation system in the compartment.In our country, the air-conditioning system in railway passenger car control the temperature through start-stop condition, so the temperature fluctuation is obvious, and the air environment can't satisfy the passenger's demand. In the study of 25K passenger car, PID and FUZZY control system are designed by simulink tool box of the Microsoft MATLAB to control the temperature in the compartment. Based on the condition that the CO₂ concentration is much high, and the air quality is bad in the compartment, the CO₂ concentration is regarded as control standard, and PID control system is designed and simulated. The results show that controlling fresh air volume based on CO₂ concentration can effectively implement improving the air quality in the compartment.