Majority of slurry pipelines operates at flow velocities high enough to maintain all transported solid particles in motion. Nevertheless, it happens sometimes that pipeline operations with stationary deposits of solids at the bottom of a pipe are found in practice (e.g. sand transportation through long pipelines connected with a dredge). Many different models are available for a prediction of the pressure drop in a slurry pipe without a deposit. Very little is known about flows with stationary deposits. The paper discusses pipe flows of sand-water slurries at velocities lower than the deposition-limit velocity. Results of laboratory tests of slurry flows with granular beds at the bottom of a slurry pipe are analyzed with an aim to establish a predictive model for the frictional pressure drop associated with this type of slurry flow. The pressure-drop model is based on a description of prevailing mechanisms that are identified to govern solids dispersion and solids friction in slurry flows at different conditions (e.g. different average concentrations of solids above the stationary bed, different dimensions of the discharge area above the bed etc.). The proposed model is composed of continuity, momentum, boundary-friction and particle-dispersion equations. The empirical stratification-ratio equation relates the effect of particle dispersion within the slurry flow with the flow friction at the top of the stationary deposit. This friction is recognized as a major contributor to the total pressure drop in the slurry flow through a pipe with a stationary deposit.

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