APPARENT WALL SLIP VELOCITY COEFFICIENTS IN CONCENTRATED SUSPENSIONS OF NONCOLLOIDAL PARTICLES

The apparent wall slip velocity coefficient of concentrated monodisper se suspensions of 90 mu m PMMA particles in a viscous Newtonian fluid was determined experimentally in a narrow gap Couette device by measur ing the particle velocities across the gap using a laser doppler anemo meter system and then extrapolating the results to the two walls. The slip coefficients thereby obtained were found to be insensitive to the magnitude of the applied shear rate and to equal, approximately, lamb da/8 for particle concentrations phi in the range 0.45 less than or eq ual to phi less than or equal to 0.52, where lambda refers to the rela tive effective viscosity of the suspension with respect to that of the pure fluid. (C) 1995 Society of Rheology.