Yield shear stresses and shear rates at a valve wall are derived from experimental results on a series of concentric cylinder valves. The fluid constitutive equation used for this purpose is that of a Bingham Plastic. Valve plates (which are such that the radial gap is small compared to its mean pitch) are taken to be parallel so far as the derivation of the flow ν's pressure ν's geometry model is concerned. A range of electrode separations from 0.5 to 1.0mm are used with flow velocities being limited to the region where the viscous pressure drop component is below that caused by the electro stress. Results show that (away from the region of low shear rates and high voltages) the wall stresses for equivalent conditions are comparable for different valves, for a range of applied field strengths and mean flow velocities. Thus, provided the hysteretic region is avoided the fluid can be treated as a Bingham continuum with some stated reservations. However, this is only applied with precision for the truly corresponding situations defined in the paper.
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Peel et al. (1994) studied this question.