Slurry transport, fully stratified flow in the sliding flow regime

Wilson in his books and publications talks about fully stratified flow. In the 4-component model of Sellgren & Wilson the 4th component is fully stratified flow (Sellgren & Wilson, 2007). The criterion of fully stratified flow as mentioned by them is a particle diameter to pipe diameter ratio larger than 0.015. It is assumed that above a sliding bed there is no suspension. A good physical background for this criterion could not be found, nor a good description of the concentration distribution. Most probably the advection diffusion equation is not valid anymore for very large particles, so existing solutions for the concentration distribution cannot be used. The paper gives the derivation of the criterion of fully stratified flow, based on the assumption that the sedimentation flux is larger than the erosion flux. This implies that particles cannot escape from the bed or the sheet flow layer. An equation for the criterion of fully stratified flow is presented and validated with experimental data. A model for the concentration distribution in fully stratified flow is also presented and validated with experimental data.