Aerosol Deposition by Diffusion in Microchannels

Farzan Tavakoli (1), Sushanta Mitra (1), JASON OLFERT (1)

(1) Department of Mechanical Engineering, University of Alberta.

     Abstract Number: 855
     Last modified: August 10, 2010

Abstract
The problem of diffusion losses and particle concentration of ultrafine aerosols on the walls of microchannels has been investigated. Penetration efficiency, defined as the fraction of exit and inlet particle concentrations, have been investigated for microscale channels. Although many analytical and semi-analytical solutions for the convection diffusion equation have been proposed, none of them are appropriate for microscale geometries. Here we considered the slip regime for the gas flow in the channels. Moreover, new studies show that zero particle concentration for the wall boundary conditions does not hold when the geometric length of the problem is in microscale or when the operating pressure is low. Thus, new boundary conditions have been applied for both velocity and concentration on the walls for the microchannels. The velocity of gas on the walls is not zero and particle concentration on walls is nonzero and proportional to the particle flux to the wall. It has been shown that even when all the particles stick to the wall after impact, the concentration on wall does not become zero. However, the magnitude of the particle concentration is so small that it does not have a significant effect on the penetration. In this study, the convection diffusion equation is solved numerically using a finite difference method. New equations have been proposed for the penetration of microchannels in the gas flow slip regime as a function of the dimensionless deposition parameter and channel Knudsen number.