A NEW CORRELATION FOR THE AEROSOL DEPOSITION RATE IN VERTICAL DUCTS

A numerical simulation of the motion of spherical, surface charge-free , monodisperse polystyrene particles having dimensionless relaxation t imes, tau(+), ranging from 0.1 to 50 was performed in a fully turbulen t channel flow with a friction velocity of 60 cm/s. The motion of the particles is governed by the modified Maxey-Riley equation which inclu des the wall-corrected Stokes drag force, the wall-induced and shear-i nduced lift force, and the Brownian random force. The nonlinear drag c orrection, particle-particle collisions and the feedback effect of the particles on the fluid were not considered because the particles are small and assumed to be very dilute in the flow field. The particle de position rates were obtained for both monodisperse and lognormally dis tributed polydisperse particles. It was observed that, for a given tau (+), the deposition rate depends strongly on particle polydispersity. Monodisperse particles always have the lowest deposition rate if compa red with polydisperse particles. The deposition rate can be increased by three orders of magnitude when the particles' geometric standard de viation, sigma, increases from 0 to 0.45. For particles with the same sigma, the deposition rate can be higher if one determines it by weigh ing the deposited particle mass instead of counting the deposited part icle numbers. It was also observed that, for a given particle density and flow field, there is a minimum deposition point which takes place at tau(+) approximate to 1 for polystyrene particles. This minimum dep osition point will shift to a lower tau(+) value as the particles' pol ydispersity increases. Because of the strong dependence of deposition rate on particle polydispersity, it is crucial to correlate deposition rate with both tau(+) and sigma. (C) 1995 Academic Press, Inc.