Scale-up study of aerated coaxial mixing reactors containing non-newtonian power-law fluids: Analysis of gas holdup, cavity size, and power consumption

Abstract

The use of coaxial mixers has significantly improved gas dispersion in non-Newtonian fluids. However, to the best of our knowledge, no scale-up investigation of an aerated coaxial mixer has been reported in the literature. This study aims to explore the gas hold-up, energy dissipation rate, power consumption and cavity size in order to provide the guideline for scaling-up of the coaxial mixers. Through the use of computational fluid dynamics and electrical resistance tomography, the effects of the aeration rate, central impeller type, rotating mode, impeller speed, and pumping direction on the gas dispersion efficacy in both small-scale and large-scale coaxial mixers containing non-Newtonian fluids were investigated. For the coaxial mixer in the co-rotating mode, the same flow regime was achieved when the central impeller tip speed and the anchor impeller rotational speed were kept constant in both small-scale and large-scale systems. It was observed that maintaining the aeration rate per volume of the non-Newtonian fluid constant was beneficial to preserve the performance of the large-scale coaxial mixer the same as its small-scale counterpart. The use of specific power consumption as a scale up criterion effectively improved the energy dissipation rate uniformity, which is critical for shear sensitive applications.