Turbulent particle deposition in a rectangular chamber: Study of the effect of particle size and ventilation regimes

Abstract

The interaction of aerosol particles with wall surfaces is important in modeling their behavior. This interaction is usually represented in theoretical models as a loss term. The loss rate is the rate at which particles deposit or react with the surfaces. This loss term is important in many branches of aerosol science including human health and indoor air quality. Increased surface deposition usually means lower concentrations of airborne particles and hence, lower exposure to the inhabitants. If the efficiency of the particle deposition is influenced by factors other than the particle size, such as a natural convection of the air, this has to be taken into account to evaluate the results. In this research, test aerosol sized from 15 nm to 3 μm are produced by several different aerosol generators; the gas burner, the Collison nebulizer, the condensation aerosol generator, the orifice atomizer and the Vibrating Orifice Aerosol Generator (VOAG). A rectangular chamber whose dimensions are 75 x 75 x 180 cm3 was used in this study. The particles were injected into the chamber, with a known ventilation and the concentration decay was monitored by the Ultrafine Condensation Particle Counter (UCPC) and Optical Particle Counter (OPC). During the measurement, the air inside the chamber is moved by natural convection and ventilation effect. The results shows that the particle loss rate under the higher air exchange rate is larger and this is not only due to air exchange itself but also the wall deposition. The theoretical model presented by Benes and Holub (1996) agree with the experimental data better than the Crump and Seinfield (1981) model with the hypothesis of Plandtl`s mixing length. 118 refs.