Friction reduction in pipe flow of coarse slurry by fines addition – experimental study.

Very coarse basalt-water slurry forming fully stratified flow with a sliding bed and producing considerable friction loss was tested in a laboratory pipe. A considerably finer fraction of sand was added in steps to gradually increase the concentration of this fraction in the flowing slurry. The frictional pressure drop was measured together with the slurry discharge and slurry density. Furthermore, solid particles and their motion were observed at the bottom of the pipe. This observation indicated that finer particles in basalt-based bimodal slurry flows positioned themselves below the coarse particles at the pipe wall. The experimental results show that a quite small amount of fines is sufficient to produce a considerable friction reduction in settling slurry flow. Furthermore, the results indicate that there is a certain optimum quantity of fines at which the maximum reduction is reached and further addition of the fines does not bring any further improvement. [ABSTRACT FROM AUTHOR]