Viscoelastic Characterisation of Low-grade Molasses By Jet-Swell Measurements

摘要

Previous studies have established that the viscosity of low-grade molasses nad massecuites depends on the shear rate, temperature and composition. It has also been hinted that these fluids are not merely viscous but rather viscoelastic. This result is not unexpected, given the presence of dissolved high polymers (polysaccharides). After a brief eneral discussion of fluid rheology, this paper describes an experiment performed on Queensland low-grade molasses to exhibit its viscoelasticity. When forced from a pipe, viscoelastic fluids swell markedly. A photograph of such an event is presented here and also used to estimate the fluid's viscoelastic relaxation time. The result, about a tenth of a second, is consistent with the values determined for French beet molasses using a Weissenberg rheogoniometer. The estimated relaxation time is used to assess the possible impact of viscoelasticity in two factory processes: stirring in cooling crystallizers and flow through pipe fittings. It is concluded that viscoelasticity may play a role in the known tendency of low-grade massecuites to short-circuit in vessels of complex geometry and also may explain the anomalous published pressure-drop data for molasses flow in pipe-fittings.