On slip effects in steady-state flow measurements of oil-in-water food emulsions

The problem of the wall slip in steady-state flow measurements of oil-in-water (o/w) food emulsions has been investigated for different sensor system geometries and surface profiles. Experimental results demonstrated that slip effects are strongly dependent on the type of emulsion studied This may be related to the emulsion microstructure. Thus, for instance, a highly structured gel-like continuous phase dampens wall slip effects, as opposed to emulsions in which creaming appears as a mechanism of instability because of the formation of particulate flocs. The occurrence of wall slip is more clearly observed if the flow curves are obtained from stress sweep experiments. Although the recovery of the steady-state viscosity of a presheared sample is generally complete (similar values at low and high shear rates), the appearance of slip effects may be favoured by emulsion preshearing. (C) 1998 Elsevier Science Limited All rights reserved.