Modeling of magnetorheological fluid centrifugal sedimentation using the kinematic waves theory

Sedimentation of carbonyl iron microparticles (CIP) in magnetorheological (MR) fluids is an inherent phenomenon driven by the density difference between the fluid’s phases. In rotary MR clutches, the high centrifugal accelerations substantially amplify this effect, specifically for power transmission applications where accelerations are held for long durations. The mechanics describing the segregation of CIP from MR fluid under high acceleration fields in hundreds of g is yet unknown. To describe the phenomenon, this paper proposes a mathematical description of the motion of the CIP under centrifugal acceleration and verifies model predictions with experiments. The model is based on the theory of kinematic waves for centrifugal acceleration, here adapted for MR fluid. Centrifugation tests are performed in a LUMiSizer centrifuge using a MR fluid formulation without typical additives. The fluid has a particle concentration of 37% v/v, which is typical for clutch applications. Results show that the model accurately predict particle dynamic above 60 g and up to 2325 g . Below this threshold, discrepancies emerge, mostly attributed to the thixotropic properties of MRF and the determination of the flux function. These results show that kinematic waves theory captures the key mechanisms of MR fluid centrifugation for the tested formulation, while highlighting the need for further work to extend its applicability to a broader range of MR fluids with different particle concentration, size distribution and additive packages.