| Electrorheology is the study of the effects of electric fields on the flow properties of certain fluids. These fluids generally exhibit an increase in apparent viscosity and a greater yield stress over an unelectrified sample. The phenomenon requires an electric field and polar particles suspended in an insulating oil. A standard concentric cylinder viscometer, fitted with custom made electrical attachments, was converted into an electrorheometer. This system allowed for control of the applied DC voltage, fluid temperature, and shear rate while observing, the resulting effects on the shear stress. Two electrorheological fluids, milk chocolate and suspensions of wheat flour in oil, were the materials examined in this study.;An experimental design was applied to the flour and oil systems to test for significant effects and interactions among six important electrorheological variables: voltage, temperature, concentration, flour type, oil type, and moisture content. One of the variables, flour type, had no effect on the electrorheological response. At constant temperature, the shear stress increases as the voltage increases for all fluid systems studied. Also, shear stresses increase as temperature increases when fluids are subjected to a constant shear rate and voltage. Although this response may have been predicted for flour and oil suspensions, these results were unexpected for a typical shear-thinning food, milk chocolate.;Because a single mechanism explaining the electrorheological phenomenon has yet been identified, dimensional analysis was applied to each electrorheological system in attempts to model the response. Ten dimensionless groups were collected and manipulated to create meaningful terms, like the Mason number--a ratio of polar and viscous forces. Multiple regression was applied to the dimensionless groups, and equations were developed to predict flow behavior for each fluid system.;The effects of an applied voltage on the thermal conductivity of molten milk chocolate was also studied. An applied electric field of up to 450 V mm... |
