SEDIMENTATION AND SEDIMENT FLOW IN SETTLING TANKS WITH INCLINED WALLS

The flow of a sediment layer that forms on an inclined plate as a cons equence of the steady sedimentation of spherical particles was investi gated theoretically as well as experimentally. The theoretical analysi s was based on the model proposed by Nir and Acrivos (1990), modified to include shear-induced diffusion due to gradients in the shear stres s as well as a slip velocity along the wall due to the finite size of the particles. The resulting set of partial differential equations, wh ich is amenable to a similarity-type solution both near the leading ed ge as well as far downstream, was solved numerically using a finite di fference scheme thereby yielding theoretical predictions for the parti cle concentration and velocity profiles, plus the local sediment layer thickness, all along the plate. In addition, a new experimental techn ique based on laser Doppler anemometry was developed and was used to m easure the particle velocity profiles in the highly concentrated sedim ent layer as well as the corresponding slip coefficient which relates the slip velocity to the velocity gradient adjacent to a wall. The thi ckness profile of the sediment layer was also measured experimentally by means of video imaging. It was found that the experimental results thus obtained for the particle velocity profile and for the local sedi ment layer thickness were in very good agreement with the correspondin g theoretical predictions especially considering that the latter did n ot make use of any adjustable parameters.