The effect of re-entrainment on particle deposition

Abstract

The effect of particle removal on observed deposition rates is considered by combining previous sublayer analyses. Wall shear stress is shown to be a controlling parameter; below a critical value where removal can occur, deposition varies linearly with time but above this value the observed deposition rate is dependent on the choice of time interval over which measurements are made. For monodisperse particles, a discontinuity in deposition plot is predicted although this may be smoothed out for particles with a wide size distribution. It is suggested that the measurement of the critical wall shear stress may be useful for estimating adhesion forces under dynamic conditions such as occur for redeposition problems. The functional dependence of deposition on wall shear stress for combined deposition and removal has been derived for the cases where diffusional, inertial and gravitational forces are dominant. Comparison with data from the literature confirms the general trends but precise matchings have not been attempted.