Kinetic models for particle resuspension in turbulent flows: theory and measurement

Measurements are reported of the short-term resuspension of nominal 10 and 20 mum alumina spheres and graphite particles from a polished stainless-ste el flat plate in fully developed turbulent channel how. Preliminary measure ments were made of the normal and tangential forces holding the particles o nto the surface. Whilst both forces had a broad spread and were on average much reduced in value compared to that for smooth contact, the average tang ential force was typically of order 1/100th of the average normal adhesive force, suggesting as has been reported previously that drag forces can play a more important role in esuspending a particle than lift forces. The resu spension measurements are compared with predictions of the RRH (1988) kinet ic model based exclusively on lift/normal forces and those of a rock'n roll kinetic model that involves the rocking of a particle about an asperity (t he motion being dominated by the drag force). The RRH model consistently un der predicted the amount of resuspension in contrast to that of the rock'n roll model which gave values much closer to the measured resuspension. As i n the RRH model, the rock'n roll model admits the possibility of removal of particles by resonant energy transfer. However the results indicate, at le ast for the cases considered, that this contribution is generally small, in which case the resuspension rate constant reduces to the form appropriate for a balance of moments due to adhesion and aerodynamic forces about the s urface asperities at the points of contact. Under these 'quasi-static' cond itions a simpler and more exact model for resuspension can be constructed: however in practice for a Gaussian distribution of removal forces this give s very similar results to the original rock'n roll model. The formula for t he resuspension rate constant under 'quasi-static' conditions has similarit ies with the empirical formulae proposed by Wen and Kasper (1989) on the ki netics of particle re-entrainment from surfaces. Journal of Aerosol Science , 20, 483-498, although there are important differences in interpretation. (C) 2000 Elsevier Science Ltd. All rights reserved.