EXPERIMENTAL AND NUMERICAL STUDIES ON MIXING OF YIELD-PSEUDOPLASTIC FLUIDS WITH A COAXIAL MIXER

Abstract

An anchor coaxial mixer is a combination of an anchor impeller and a central impeller. The central and anchor impellers provide the shear and bulk flows within the mixing tank, respectively. The agitation efficiency is governed by the proper design of this mixing system. In this study, the effects of the central impeller speed, anchor impeller speed, operation mode, and the speed ratio of an anchor-Scaba coaxial impeller were evaluated on its power consumption, mixing time, and flow pattern using electrical resistance tomography (ERT) and computational fluid dynamics (CFD). An ERT system with a five-plane assembly of peripheral sensing rings, each containing 16 stainless steel electrodes, was utilized to measure the mixing time for this coaxial mixer. The sliding mesh (SM) technique in the CFD analysis with the modified Herschel-Bulkley model was applied to simulate the impeller rotation and the rheological behavior of the xanthan gum solution (a pseudoplastic fluid possessing yield stress). To validate the model, the CFD results for power consumption were compared to the experimental data. The mixing times were correlated using the specific power consumption model.