Using positron emission particle tracking (PEPT) to study nearly neutrally buoyant particles in high solid fraction pipe flow

Positron emission particle tracking (PEPT) allows the flow path of a tracer particle to be followed in opaque flows. It has been used here to study particle trajectories and velocity profiles of a single radioactively labelled tracer particle in high solid fraction, solid–liquid pipe flow. Experiments studied 5 and 10 mm almost spherical alginate particles, of specific gravity 1.02 in a 45 mm internal diameter pipe positioned either vertically or horizontally. Solid delivery concentrations from 20% to 40% v/v were investigated in carrier fluids of 120–500 mPa s mean apparent viscosity, with mean mixture velocities of 20–125 mm/s. Different flow patterns were identified and studied including concentric and capsule flow. A slow-moving annular region of particles near the pipe wall was measured when high viscous carrier fluids and/or small particles were used. The asymmetry of the horizontal velocity profiles was found to depend strongly on the solid concentration and the particle Reynolds number. Results are especially relevant to food and bioproduct flows but show the relevance of the technique to the study of solids conveying.