The electrorheological effect in static squeeze-flow

The static behaviour of an Electrorheological (ER) fluid in squeeze-flow is investigated both theoretically and experimentally for three types of loading condition namely single and superimposed loading when the fluid in energised by a constant potential, and superimposed loading when the fluid in energised by a constant field. From the experimental work an empirical equation for yield stress as a function of field is derived and there are found to be two values of the exponent in squeeze mode depending on the type of loading. The exponent obtained under single loading is consistent with that commonly quoted for ER fluids in shear mode while the exponent obtained under superimposed loading upon application of a constant potential is seen to be much larger. The theoretical analysis was successfully applied to modelling an ER fluid in static squeeze-flow. Comparison of theoretical and experimental results shows good agreement between them. The distributions of the electric field strength and field lines are investigated for parallel circular electrodes and whilst the value of the field is almost uniform in the middle regions of the inter-electrode space, there is an extremely high field existing around the edges of the space. The existence of this non-uniform edge field causes a back pressure which inhibits the radial movement of the fluid from the space between the electrodes. (author)