Vertical Axis Inductance Monitoring System to Measure Stratification in a Column of Magnetorheological Fluid

This paper addresses an automated method and experimental apparatus to measure the sedimentation of magnetorheological fluids (MRFs) in a vertical column. The automated vertical axis inductance system (AVAIMS) developed at the University of Maryland monitored the particle concentration (i.e., particle volume fraction) of an MRF as a function of column height and standing time through an automatic process of scanning with an inductance sensor driven by a stepper motor. With the acquired data, the extent and the concentration gradients of four distinct sedimentation zones were monitored and automatically determined without human decision-based post-processing of data: supernatant zone, original concentration zone, variable concentration zone, and sediment zone. The evolution of these sedimentation zones provides a characterization of an MRF's sedimentation behavior. Insights gained from these studies enable a better understanding of the dynamics of hindered settling of MRFs in closed systems, such as in rotary or linear stroke magnetorheological energy absorbers. An MRF sample consisting of carbonyl iron powder in a silicone carrier fluid with an initially uniform 21% particle volume fraction (hereinafter 21 vol%) was synthesized to demonstrate the method and the automated analysis of the AVAIMS. The 130 mm fluid column was scanned from top to bottom in 0.5 mm increments every 3 h for a total sedimentation period of six days (144 h). The results proved to be comparable to the characterizations obtained from our previous study with a manually operated VAIMS.