Numerical Simulation Of Transport Characteristics Of Indoor Particle Under The Column Attached Ventilation

Exposed to the foul indoor environment full of particulate matter created by HVAC,which seriously does harm to people’s health,and resulting in significant increase in incidence and mortality.Although Column Attached Ventilation（CAV）has been a new efficient,energy-saving ventilation,the air distribution of direction from bottom to top easily causes particles to resuspend or bring low-level particles into the occupied zone,or even the height of the breathing zone,resulting in deterioration of indoor air quality.This article uses numerical simulation to research the influence of different parameters such as location of pollution source,particle size,the volume of supply air,the supply temperature,location of outlet on the dispersion of particles under CAV mode.Evaluate the pros and cons of CAV from the perspectives of airflow field,particle concentration distribution,and blowdown efficiency.The study found that among the particles with a particle size≤20μm,only 20%can be blown up and finally discharged through outlets by the airflow,the other are deposited on the surfaces indoors,of which the most deposited on the vertical walls.Particles with a particle size of≥50μm cannot be blown up and discharged,most of which are deposited on the floor.Particles have the same motion law with a particle size≤10μm(PM₁₀),which have excellent characteristic of following air,and are not affected by particle size and the different release height.Whether the particles with particle size range of 20μm can be transported upward and discharged is determined by the volume of supply air.The volume of supply air and the temperature difference between supply air and occupied zone have a little influence on the dispersion of particles indoors.An increase in the volume of supply air can dilute the concentration of particles and increase the mass of PM₂₀discharged.The change of the supply air temperature difference will affect the air distribution of CAV.Excessive supply air temperature difference is bad for the vertical transportation and discharge of particle,and greatly reduces the blowdown efficiency.For cooling mode,excessive supply air temperature difference will weaken the vertical convection of air,leading to vertical diffusion particles reduced.For heating mode,excessive supply air temperature difference directly weakens the secondary attachment airflow on the ground,and also weakens the vertical transportation of particles.Therefore,the design principles of large air volume and small temperature difference should be followed in real engineering application.The pattern of airflow improved with the change of height of outlets,leading to the change of movement of particles.Outlets closed to the pollution source is good to eliminate the particles efficiently,which decreases the particle concentration indoors,and improves the sewage efficiency of PM_2.5by 75%and of PM₂₀by 130%compared to the circumstance where outlets located on ceiling.Outlets located in occupied zone is most disadvantageous to eliminate particles.At the same time,as long as the outlets are located at the height of occupied zone or even lower height,the ventilation efficiency can be increased by 10%.This paper researches the dispersion and deposition of particles in CAV mode,which further expands the field of research related to indoor air quality in CAV,and optimizes the method of design for better application.