This study investigates the sedimentation mechanism of magnetorheological fluids (MRFs) in a vertical column based on Kynch theory. The stratification and main factors affecting the sedimentation of magnetic particles in MRFs are analyzed theoretically. An vertical axis inductance monitoring system AVAIMS allows for tracking the particle concentration (i.e., particle volume fraction) discontinuities due to the sedimentation of MRFs including the mud-line, the gel-line, and the cake-line. The sedimentation progress of MRFs can be evaluated by analyzing these boundaries. In this study, the extent and concentration gradients in four distinct sedimentation zones (i.e., supernatant zone, original concentration zone, variable concentration zone, and sediment zone) were monitored using an MRF sample with a particle concentration of 20% volume fraction for seven consecutive days. The tests show the effectiveness of Kynch theory to describe the sedimentation progress of MRFs. MRF samples with different volume fractions (i.e., 5, 10, 15, 20, 30 and 40 vol%) were synthesized, then the sedimentation velocity of the MRF was obtained by examining the mud-line descent of each sample. Based on the mass flow conservation equation and particle sedimentation velocity model, the concentration propagation velocity was obtained. The concentration of the sample when the gel-line and the cake-line appear and the maximum concentration the sample can reach was obtained to better understand sedimentation progress.

Magnetorheological fluids,Sedimentation mechanism,Sedimentation velocity,Concentration propagation velocity