Particle image velocimetry applied to suspensions of millimetric-size particles using a vane-in-a-large-baffled-cup rheometer

Millimetric particles suspended in four different fluids were sheared and video-recorded using a controlled-stress rheometer with a four-blade vane-in-a-large-cup. Experimental situations where the suspension next to the vane moves as a solid cylinder, i.e., where the Couette analogy can be applied, were determined. Velocity fields were measured by particle image velocimetry (PIV) in various suspensions: resin particles in oil (creamed particles), resin particles in water (settled particles), acetate particles in glycerin, and uniformly suspended gelatin particles in a commercial beverage. Data were expressed in terms of the Reynolds number calculated from experimental angular velocity measurements. The suspensions revealed flow patterns which include a considerable amount of vortices initially originating close to the millimetric-size particle bed and thereafter distributing and spreading within the large-baffled-cup. Flow characterization with a vane-in-a-large-cup was only possible for acetate particles in glycerin undergoing laminar flow, as verified by PIV and magnitude of the Reynolds number. Average shear stress and shear rate values were calculated and results for the suspension viscosity were in agreement to those predicted by the model of Happel (Viscosity of suspensions of uniform spheres. Journal of Applied Physics, 1957, 28(11), 1288–1292).