Distribution of Medium-to-Coarse Glass Beads in Slurry Pipe Flow: Evaluation of Measured Concentration Profiles

Concentration distribution of two fractions of glass-bead (ballotini) particles (medium size 0.44 and 0.53mm, respectively) in flows of heterogeneous slurry was measured in a laboratory pipe of the internal diameter of 100mm using a radiometric device. Particles in such flows are supported by both interparticle contacts and turbulent eddies and the solids load must be considered as combined load composed of both contact and suspended load. Flows tend to be partially stratified and if high concentrated (mean volumetric concentration of solids higher than approximately 20%) they exhibit a sliding bed. It appears that two most common methods to calculate concentration profiles in settling-slurry flows are not able to handle the sliding bed adequately. A comparison of the test results with the Gillies-Shook model for combined-load flows shows that the modeling approach requires further refinements. An application of the more recent Kaushal-Tomita model based on the turbulent-diffusion concept is inappropriate in high-concentrated slurries composed of medium-to-coarse grains. A simple one-dimensional model is proposed that takes conditions for an existence of a sliding bed into account and predicts a simplified concentration profile in stratified flows composed of a sliding bed and a transport layer above the bed.