Diffusion Characteristics And Prevention Technology Of Respiratory Pollutants In Train Compartments

As one of the most important modes of transportation in my country,high-speed trains have the characteristics of large passenger capacity and developed transportation network.However,the interior environment of the car is closed and densely populated,which easily leads to the accumulation of pollutants and the airborne transmission of viruses.In recent years,various respiratory diseases have emerged one after another,causing huge losses and impacts on the global economy and society.In the context of the normalization of the epidemic,it is of great significance to study the characteristics of the flow field and pollutant diffusion in the train compartment and the optimization of the corresponding prevention and control technology to protect the comfort and safety of passengers.Based on the Computational Fluid Dynamics theory,the effects of exhaust and air supply modes on the flow field characteristics and the diffusion characteristics of respiratory pollutants in the cabin were numerically simulated.Combined with the Wells-Riley method quantitatively evaluated the probability distribution law of passengers infected.Based on the optimized ventilation scheme and the two-end exhuast scheme,a ride layout method conducive to reducing the probability of cross infection is studied.Firstly,taking the celling air supply scheme as an example,the effects of four exhaust schemes on the flow field characteristics and the diffusion characteristics of respiratory pollutants in the train compartment were studied,including the two end exhaust,the lower end exhaust,the upper end exhaust and the asymmetric upper end exhaust,and the ventilation system of the train compartment was evaluated by using relevant indicators.The results show that the ventilation efficiency is 0.27 when exhaust air is used at both ends,which is relatively low and the diffusion range of respiratory pollutants is relatively wide.When using the upper exhaust,the ventilation efficiency is 1.06,and the diffusion range of the pollutant can also be effectively controlled.However,the air supply flow tends to deviate to the side of the carriage,resulting in poor temperature uniformity.This phenomenon can be effectively resolved by adjusting the flow distribution ratio of both sides of the exhaust port.Under this type of compartment environment and ventilation scheme,the Passengers of the column B are easily affected by the respiratory contaminants of passengers of the column C.Secondly,for the upper exhaust with relatively better ventilation efficiency,the flow field characteristics and the diffusion characteristics of respiratory pollutants in the train compartment under six air supply schemes are comparatively studied,including celling air supply,lower air supply,celling air supply + lower air supply,local celling air supply,side top air,local celling air supply + side top air supply.And use the relevant indicators to evaluate the ventilation system in many aspects.The results show that by adjusting the flow distribution ratio between the various air vents,it can effectively avoid the phenomenon of short-circuiting in the car.When using the lower air supply,the energy utilization factor and the ventilation efficiency in the compartment are as high as 1.38 and 1.21,but the ride comfort in the cabin is relatively poor.When using a celling air suplly,a celling air suplly + lower air,and the side top air suplly,each evaluation index is relatively good.However,the airflow vortex in the compartment will result in the Passengers of the column B are easily affected by the passengers of the column C.The local celling air suplly can effectively alleviate the above phenomenon,so that the contaminant concentration is lowered to 1882 ppm(Parts Per Million),but it will reduce the slight reduction of each evaluation index.Then,taking an optimized ventilation scheme as an example,combined with the WellsRiley risk assessment model,the infection probability under full load conditions was studied and analyzed.And compared the airflow tissue characteristics and risk assessment characteristics under the four ride layout schemes.The research results show that the change of the passenger layout will have a greater impact on the flow field characteristics and pollutant diffusion characteristics in the cabin.When passengers are in column C,the probability of infection caused by their breathing pollutants is relatively greater.Through comparison,it is found that the cross-infection probability between passengers can be effectively reduced when using cross rides and avoiding taking the column C.Finally,taking a standard EMU in operation as an example,which use two end exhaust,a car model with a complete air duct is established.For summer and winter,the flow field characteristics under full load conditions and the pollutant diffusion characteristics under half load conditions are studied respectively.At the same time,a quantitative assessment of the infection risk in the cabin was carried out by Wells-Riley method,and a study on the layout of the ride was carried out.The research results show that when the exhaust air at two ends is used,the diffusion characteristics of passengers’ respiratory pollutants and the distribution law of the infection probability caused by them have a great relationship with the horizontal row position.When passengers are located in the front half or rear half of the cabin,their respiratory pollutants mainly spread to the front or rear end of the cabin,and mainly infect the passengers in front or rear.As passengers continue to approach the middle of the passenger room,the wider the spread of their respiratory pollutants,the more likely it is to cause virus infection.Therefore,it is recommended that passengers avoid riding in the middle of the cabin,and try to ensure that the number of passengers in the front half and the rear half of cabin is basically the same.