Effect of concentration on enhanced sedimentation rate of erythrocytes in an inclined vessel.

The enhanced rate of sedimentation of erythrocytes in an inclined rectangular vessel was measured under microscopic and macroscopic conditions. The velocity profile, V(x), and the thickness, delta, of the upflow layer generated below the downward-facing wall in the sedimentation vessel were measured under a microscope with polystyrene latex as a tracer particle. Here, x is the distance from the vessel wall. All the data of the velocity profile are represented by a single curve, [Vmax- V(x)]/Vmax = [(delta -x)/delta]2, irrespective of the volume fraction, H, and tilt angle, theta, in the range of 0.05 < H < 0.30 and 10 degrees < theta < 40 degrees, where Vmax is the maximum velocity found at the upflow boundary. The rate of fall of the top surface of the suspension v(H, theta) fits the function, v(H, theta) = v(0, theta)(1-H)exp[-(aH + bH2)], well, irrespective of H and theta. These experimental results are compared with the theory of Acrivos and Herbolzheimer.