MIXING OF NEWTONIAN AND NON-NEWTONIAN LIQUIDS - SCREW AGITATOR AND DRAFT COIL SYSTEM

Mixing efficiency and power consumption have been investigated for several Newtonian and non-Newtonian liquids in a novel system consisting of a screw agitator rotating in a draft coil. For Reynolds numbers larger than 50, the inertial forces increase the pumping capacity of the screw impeller and hence its mixing efficiency. Shear-thinning effects can be accounted for by taking the effective rate of deformation to be proportional to the impeller rotational speed. Elasticity effects could be satisfactorily correlated with the Weissenberg number. The ratio of the mixing time to the average circulation time is constant. The power number could not be correlated with the Reynolds number; however, the ratio of the power number to the circulation number is inversely proportional to the Reynolds number for Newtonian as well as for shear-thinning inelastic fluids. The power consumption for elastic fluids is much larger.