STUDY OF THE FLOW BEHAVIOR OF ELECTRORHEOLOGICAL FLUIDS AT SHEAR-MODEAND FLOW-MODE

In this study the rheological properties of two electrorheological (ER ) fluids (experimental samples) under the influence of an AC as well a s under DC conditions are investigated using a rotational viscometer. Plastic-fluid behavior quite well describes the flow curves with a yie ld stress which depends upon the applied electric field. The results s how that the behavior of an ER-fluid depends on its composition. Compa rison between the shear-type (rotational viscometer) and flowtype (sli t flow) measurements leads to the hypothesis that the inhomogenous ele ctric field (in viscometer) may be the cause for an increase of the me asured ER-effect relative to that measured in a homogeneous field (cha nnel with smooth electrodes). Based on this hypothesis, the ER-effect in slit flow should increase by altering the electrode morphology. For that purpose, the effects of the electrodes morphology on the slit fl ow of an ER-fluid are studied via laser-Doppler-anemometry (LDA). Two types of grooved electrodes were used. In the presence of an AC-field, the ER-effect with grooved electrodes is greater in comparison to the case of smooth electrodes at the same field strength and pressure dro p. An average factor of 2.5 describes this increase. This increase in the ER-effect is accompanied by a decrease in electric current. Under a DC-field the ER-effect with grooved electrodes is somewhat better th an the smooth electrodes but only at very low field strength. Increasi ng the field strength leads to a decreased ER-effect in comparison to the smooth electrodes. (C) 1997 Elsevier Science S.A.