Piston-driven flow of highly concentrated suspensions

The piston-driven flow of highly concentrated suspensions (55% or 59% by vo lume solids) of dense spheres was investigated as a function of piston spee d, liquid viscosity, particle material, and particle size. The drag of the suspension was found to be independent of piston speed for 0.5 and 1.4 mm g lass or PMMA spheres in Liquids with viscosities from 1 to 641 cP. For susp ensions prepared from 55 000 cP liquids, the drag was piston speed dependen t. In the speed-independent range, the drag decreased with increasing liqui d viscosity and was significantly larger than that predicted by existing mo dels for suspensions. In the speed-dependent range, the drag increased with viscosity. A macroscopic model based on lubricated frictional contacts bet ween the particles and the wall was successfully applied to correlate the s hear-rate independent data for suspensions prepared from liquids with visco sities from 1 to 631 cP. It was possible to estimate the drag of the suspen sions prepared from 1.4 mm spheres by using tabulated friction coefficients and the macroscopic model. Results from flow visualization confirmed the p resence of significant wall slip and the presence of fountain flow. (C) 199 9 The Society of Rheology. [S0148-6055(99)01203-1].