Numerical Simulation Study Of Aerosol Dispersion In Building Drainage Systems

In recent years,indoor air quality has been receiving increasing attention,including the issue of aerosol diffusion.Numerous studies were conducted at home and abroad on the simulation and experimental research of indoor aerosol diffusion,primarily focusing on the impact of ventilation,air conditioning systems,and indoor activities on aerosol diffusion.However,research on aerosol diffusion in building drainage systems was still relatively weak.In this study,the diffusion law of aerosols in building drainage systems was investigated based on the CFD(Computational Fluid Dynamics)method.The research included three parts:aerosol diffusion law under the influence of chimney effect without water flow,aerosol diffusion law in drainage systems under drainage conditions,and the diffusion law of aerosols generated during drainage.(1)Driven by the chimney effect,aerosol particles released from the bottom of the building’s drainage system will disperse upward along the vertical pipes until they reach the vent cap.If the water seals in the drainage system remain intact,most of the aerosol particles will escape from the vent cap and not enter the lateral branch pipes of each floor.However,if the water seals are damaged,simulation results indicate that aerosol particles will not escape indoors below the neutralization level,but they will disperse and escape into the indoor environment above the neutralization level.Additionally,above the 4th floor,the amount of escaped aerosol particles increases with the height of the floors.(2)In the event of water seal failure,when a negative pressure is applied to the water seal at the 3rd floor below the neutralization level,the direction of airflow changes as the negative pressure value increases.This causes aerosol particles that would not originally disperse to the3 rd floor to start spreading and escaping into the indoor environment.The critical pressure value for the water seal at the 3rd floor is-2Pa.On the other hand,when a positive pressure is applied to the water seal at the 5th floor above the neutralization level,the direction of airflow changes as the positive pressure value increases.This prevents aerosol particles that would normally disperse to the 5th floor from spreading into the indoor environment.The critical pressure value for the water seal at the 5th floor is 1Pa.The negative pressure suction effect at the vent cap can counterbalance the adverse effects of the chimney effect on the floors above the neutralization level.The critical pressure value at the vent cap is-15 Pa.(3)When the drainage stack is filled with aerosol particles,during single-floor drainage,the diffusion range of aerosols gradually decreases as the floor level decreases.The order of range size is highest floor(7th floor)> intermediate floor(4th floor)> lowest floor(1st floor).During drainage on the highest floor,aerosol particles can disperse to all floors.During drainage on the intermediate floor,aerosol particles mainly disperse below the 4th floor.During drainage on the lowest floor,aerosol particles can only disperse to the horizontal branch pipes.In the drainage floor,aerosol particles do not escape.In the floor with the highest negative pressure,the number of escaping aerosol particles is relatively low.Below the floor with the highest negative pressure,the quantity of escaping aerosol particles decreases as the floor level decreases.The order of the quantity of aerosol particles captured by the pipe walls and the total quantity of aerosol particles escaping into the indoor environment is highest floor >intermediate floor > lowest floor.(4)When the drainage stack is filled with aerosol particles,during drainage from multiple floors,the order of the diffusion range of aerosol particles,the quantity of particles escaping into the indoor environment,and the quantity captured by the pipe walls is as follows:combination of 7th and 1st floors > combination of 6th and 2nd floors > combination of 5th and3 rd floors.In the case of drainage from all floors combined,aerosol particles begin to disperse to the horizontal branch pipes only in the later stage of drainage,and the quantity of dispersion gradually increases as the floor level decreases.Only the highest floor has no aerosol particle escape,while escapes occur in floors 1 to 6,with the highest quantity of escaping particles observed on the 3rd floor.The horizontal branch pipes and the ventilation cap are the areas where aerosol particle escape is most concentrated.(5)In the case of drainage from a single floor and the release of aerosol particles,the particles primarily disperse downward,beneath the drainage floor,and gradually spread into the horizontal branch pipes of the lower floors.Except for the floors above the drainage floor and the floor with the maximum negative pressure,aerosol particle escape occurs in all other floors.When drainage occurs from the intermediate floor and the lowest floor,the quantity of aerosol particles escaping through the horizontal branch pipes is greater than those captured by the pipe walls.However,in the case of drainage from the highest floor,the quantity of aerosol particles captured by the pipe walls exceeds the quantity escaping through the horizontal branch pipes.The order of the total quantity of aerosol particles escaping into the indoor environment is as follows: drainage from the intermediate floor > drainage from the highest floor > drainage from the lowest floor.(6)When multiple floors are combined for drainage and the release of aerosol particles,the combination of the 7th and 1st floors exhibits the greatest dispersion range of aerosol particles,followed by the combination of the 6th and 2nd floors.The quantity of aerosol particles escaping into the indoor environment is highest for the combination of the 6th and 2nd floors,followed by the combination of the 7th and 1st floors.In the case of drainage with all floors combined,aerosol particles only escape into the indoor environment from the right-side water seal of the releasing floor,and only the aerosol particles released from the highest floor can escape through the vent cap.No aerosol particle escape occurs in the non-releasing floors.The remaining aerosol particles are primarily captured by the pipe walls or escape through the horizontal branch pipes.