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.
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