Effects of coating on the behavior of electrorheological fluids in torsional flow

Abstract

In this paper, we report experiments on an experimental electrorheological (ER) fluid in torsional flow. The electrorheological flow properties of the ER fluid were measured using a conventional rotational viscometer (a concentric-cylinders system). Then a torsional flow device for ER fluids was designed and constructed. The flow curves measured with this device were compared with flow curves from the viscometer. The agreement between the two devices is encouraging. The addition of a PVC foil to the surfaces of the plates has been also studied. Under AC conditions the ER effect with a homogeneous coating was smaller than that in the case of no coating, but at the same time a large reduction in the current density was measured. As soon as sections had been cut out from the foil, the ER effect increased, exceeding in some cases the effect with the uncoated plates, with no significant increase in the current density. Under DC conditions, the ER effect with a coating (irrespective of the type of coating) was zero or smaller than that in the uncoated case, and the decrease of the ER effect was always accompanied by a more than proportional decrease in electric current. This implies an increase in the ER effect on the basis of the required current density. The use of a polymer mesh to coat the plates provides an increase in the ER effect in AC and DC fields. This increase in ER effect is coupled with an increase in the current density in both fields. This suggests the idea that the polarization of the polymer mesh is responsible for some of the ER effect.