DETERMINATION OF THE STEADY-STATE SHEAR VISCOSITY FROM MEASUREMENTS OF THE APPARENT VISCOSITY FOR SOME COMMON TYPES OF VISCOMETERS

Considering a number of model fluids, the relation between the (measur able) apparent viscosity eta(a) and the (true) shear viscosity eta is studied for some commonly used viscometers, like capillary, slit, plat e-plate and concentric cylinders (including the influence of the botto m of the cylinder), as well as for one laboratory type of viscometer. As long as eta is a purely monotonic function, a shift factor beta < 1 allows one to deduce eta from eta(a). Though in general variable, it frequently suffices for practical purposes to use a constant shift fac tor (the constant being characteristic of the type of viscometer used) . This does not apply to dilute solutions or any fluids with two plate au values for eta. For plastic fluids, it is shown that Casson or Bing ham behavior can - if valid at all - only describe the high shear stre ss limit of eta(a).