Investigation of three dimensional interstitial velocity, solids motion, and orientation in solid-liquid flow using particle tracking velocimetry

In this study, the advancement of Particle Tracking Velocimetry (PTV) techniques to study flows of coarse solid-liquid mixtures is reported. The method has been adapted successfully to high solid concentrations (30% and 50%) by matching the index of refraction of clear solid pieces and the carrier fluid. Digital image processing of tracer and solid piece motion recorded on stereoscopic motion picture films were used to identify solids and tracers, and obtain data on location and velocity. These studies reveal local slip velocity between phases that is dependent on solid piece shape and aspect ratio. However, the complexity of the flow necessitates the use of unprocessed velocity vector information, rather than a flow field interpolated onto a regular grid, The PTV technique may be further modified to determine solid motions and orientation distribution of high solids suspensions, by determination of Euler angles. Our results demonstrate that objects of non-unity aspect ratio tend to align along the flow, within the constraints set by solids concentration, and that such solids also demonstrate decreased rotational motion in comparison with non-elongated solids. It. is noted that elongated solids may rotate till an equilibrium position is achieved, whereupon no further rotation occurs. The results also show that, as expected, increasing solids size and concentration decreases the incidence of rotation. (C) 2001 Elsevier Science Ltd. All rights reserved.