Flow of slurries of coarse particles at high solids concentrations

Using a lock hopper feeding system, gravel and coal shale slurries containing particles of median diameter approximately 4 mm were transported at high concentrations through a pipe of I.D. 7.87 cm at velocities below 3.5 m/s−1. In addition to the usual measurements of velocity, delivered concentration and hydraulic gradient, in‐situ concentrations and particle velocities were determined. With these measurements, a two‐layer model of stratified flow of the type proposed by Wilson was examined and found to give satisfactory predictions. Coefficients of wall friction were found to vary with velocity. Minimum values of these coefficients agreed with the results of direct shear tests. This variation could be attributed to stick‐slip processes at low velocities and a change in the nature of the interparticle stress at higher velocities.