Experimental study of hydraulic transport of coarse basalt

In many industrial applications, as in dredging or deep sea mining, coarse solid particles (typical size in the order of millimeters or tens of millimeters) are transported hydraulically in mixture with water through pipelines. This paper discusses experimental results obtained for flows of water-based slurries of three fractions of coarse basalt pebbles in a 100-mm pipe of the laboratory loop of the Institute of Hydrodynamics in Prague. The collected experimental database includes concentration distributions measured in the horizontal section of the pipe loop. The data are used to evaluate friction mechanisms of slurry flow and their relation to the internal structure of the flow. Measured frictional pressure drops are analysed and compared with existing predictive formulae. A theoretical background is proposed for a modified predictive formula for the frictional pressure drop in horizontal flow of slurry carrying coarse grains transported in saltation or as a sliding bed. The relative excess pressure drop in such flow is found to be sensitive primarily to the slip ratio, the thickness of a sliding bed and the solids friction coefficient. An accurate determination of frictional energy losses is essential to a successful assessment of an economy of hydraulic transport and to an optimisation of operations of slurry pipelines conveying very coarse solids.