Pipeline flow of coarse particles in fluids with yield stresses

Abstract

Horizontal pipe flow of coarse particle slurries with carrier fluids which exhibited yield stresses were examined. Experimental measurements were made to investigate the effect the fluid yield stresses had on the transport of the coarse particles (1.7 mm and 4.4 mm) in a 52 mm diameter pipeloop. These results were used to evaluate two numerical models intended to describe these flows. Experimental tests used clay suspensions which were found to follow the Bingham fluid model. The suspensions had large yield stresses (3 to 25 Pa) which were capable of supporting the particles when the fluid was stationary. These particles were relatively large in relation to the pipe size. Slurry flows were mostly laminar but turbulent flows were also observed. The first numerical model considered the laminar flow of slurries by representing them as continua with a viscosity which varied with position in the pipe. A finite element method was used to predict the velocity distribution in the pipe from a specified pressure gradient and coarse particle concentration profile. This velocity distribution was then used to predict the concentration distribution based on a dispersive mechanism in laminar flow. The second numerical model was also mechanistically based and represented the slurries as two stratified layers with different coarse particle concentrations. This model was used for both laminar and turbulent flow. The effects of the fluid yield stresses on model predictions were considered.