Comparative analysis of aerosol particles' deposition velocities in constituent components and straight-forward sections of rectangular-shaped ventilation duct

Aerosol is one of the key factors of the indoor air quality due to the ventilation delay caused by the aerosol particles' deposition,particularly;in the rectangular duct sections in a building,which may bring about serious damage to human health.Therefore,this paper is inclined to present the results of our laboratory experiments in hoping to quantify the particle deposition velocities in a horizontally rectangular ventilation ducts made of HVAC materials(zinc-plated steel).As we know,in a steel duct system,French chalk is usually adopted to simulate the aerosol particle activities.For this purpose,we have investigated the behaviors of polydisperse aerosol particles with their mean diameters being 11.46 μm,3.63 μm,and air speeds of 2.5 m/s,5.3 m/s and 8.8 m/s.Along with the deposition velocities of the different duct sections under different air speeds and different particle sizes to the straight sections,we have also determined the abrupt contraction sections and the wind valve of the rectangular ductwork while taking into account the relation between them.Our experiments have shown that the deposition velocities are highest at the duct floor,intermediate at the duct walls and lowest at the duct ceilings.The particle size or the air speed will be increased with the increase of the deposition velocities of a given surface.As compared with the straight sections,the abrupt contraction sections,the wall and ceiling surfaces may contain obvious increment of the deposition.In addition,the deposition velocity of the cross sections of ventilation valve would surely be higher than those of the horizontal straight ones.As to the horizontal straight floors and constituent components,the velocity can surely be predicted to control the loss in the duct system.Needless to say,in the presence of the HVAC filtration,ventilation ducts are playing a minor role in determining the indoor particle concentrations.However,such velocities are expected to be important for the ventilation system contamination.Therefore,the ability to predict the degree of deposition and the locations within the ventilation ducts,particularly,at those points,where hazardous aerosols deposit may contribute to the great improvement of the efficiency of remediation and reduction of the associated costs.