Effect of shear-thinning behavior on interface renewal in partially filled single rotor mixing

Abstract

The mixing process is often used not only to homogenize the materials, but also to bring out better functions by mixing different materials. In the mixing process involving chemical reactions, it is also important to quickly remove the by-products of the reaction. In this study, a flow field around a single rotor rotating in a partially filled chamber was numerically simulated using a 3D model to examine the interface renewal characteristics of highly viscous fluids. The fluids examined were glycerin, which is Newtonian fluid, and aqueous solution of carboxymethylcellulose (CMC), which is Non-Newtonian fluid. A three-wing rotor was chosen as the mixing rotor. The evaluation of interface renewal was performed using history particles. Also, the flow states were classified into rotational, shear, and extensional flows using the Flow number to analyze the flow field. The velocity distribution obtained by the simulation was in good agreement with the experimental results under the same geometry and conditions. For distributive mixing and interface renewal, CMC results were superior to glycerin. Flow number-based evaluations showed similar flow conditions around a single rotor, regardless of the physical properties of the test fluid. However, in the case of glycerin, fluid mixing between adjacent spaces separated by the rotor wing was suppressed and interface renewals were reduced. This is because, compared to CMC, glycerin does not have a decrease in viscosity due to shear-thinning properties, and the flow rate passing through the rotor tip is relatively small. It was also shown that there was a positive correlation between the flow rate passing through the tip part of the rotor and the interface renewal, regardless of the characteristics of the mixing fluids.