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Abstract

A scanning rheometer is presented for the rheological property measurement of electrorheological (ER) and magnetorheological (MR) fluids using a non-linear viscoplastic model, based on the fluid height variation with respect to time. The rheometer basically includes a static (e.g., an overhead reservoir) or a dynamic source of fluid, a channel or slit whose sides form electrodes which are in contact with the flowing ER fluid, or a capillary tube exposed to a static/alternating magnetic field for flowing MR fluids, a transfer tube, either one or two riser tubes, and a column level detector for monitoring the column of fluid as it moves in one of the riser tubes. The column level detector is coupled to a processor which analyzes, among other things, column height vs. time data to determine both viscosity and yield stress. The rheometer overcomes one of the major drawbacks of the conventional rheometer: the inability to produce the yield stress of the ER, or MR, fluid in an absolute zero shear rate range. The results with this rheometer are compared with those obtained from a commercially-available rheometer which indicates excellent agreement.

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