SLURRY TRANSPORT THROUGH THE DYNAMIC POROSITY OF THE BALL MILL

A novel study of the fluid mechanics of slurry flow in ball mills is s hown. Both a numerical scheme called the marker-and-cell method and di rect experimentation are used in this study. First, the trajectories o f the grinding balls are calculated by the discrete-element method The n, the Navier-Stokes equations are applied to the slurry flow. These e quations are solved by means of the marker-and-cell numerical algorith m that uses a set of marker particles to determine the free surface of the slurry. This leads to the calculation of slurry velocity profile in the radial and axial directions. The numerical scheme also predicts the mill volumetric holdup, a variable that directly influences mill capacity. The results of numerical predictions were verified with expe rimental measurements. Video camera pictures of a 0.31-m diameter by 0 .61-m long ball mill with transparent end-plates are compared to the s napshots of computer-generated slurry profiles. Continuous variations in mill holdup are obtained in a 0.42-m diameter by 0.64-m long pilot- scale mill, which is supported by a special arrangement of load cells. Slurry holdup of the mill is measured for a 20-fold increase in mill feed rates and feed percent solids varying from 60 td 80%.