Centrifuge Analysis—Effects on Sedimentation Coefficients of Angular Velocity Lag, of Deviations From Stokes’ Law of Drag, and of Acceleration Effects

Abstract

Sedimentation coefficients are affected by an angular velocity lag which exists between sedimenting particles and the carrier fluid, by known deviations from Stokes’ law of drag, and by particle acceleration. These phenomena may sometimes cause orders of magnitude changes in sedimentation coefficients when the value of the dimensionless parameter wδ2/ν is greater than about 0.01, where w = angular velocity of centrifuge in rad/sec, δ = diameter of sedimenting particle, and ν = kinematic viscosity of carrier fluid. The value of wδ2/ν can easily exceed 0.01 in existing centrifuges. (Sample results are presented graphically for wδ2/ν ≦ 1000 for the case of a particle density equal to twice the density of the carrier fluid.)