Analysis of power consumption for gas dispersion in non-Newtonian fluids with a coaxial mixer: New correlations for Reynolds and power numbers

Abstract

Coaxial mixers are efficient in mixing of highly viscous fluids. The main objective of this study was to assess the power consumption for the gas dispersion in carboxymethyl cellulose solution, a power-law non-Newtonian fluid, with a coaxial mixer consisting of an anchor impeller and two central impellers as a function of the speed ratio (central impeller speed/anchor speed), fluid rheology, pumping direction of the central impeller, and the rotation mode (co-rotating vs. counter-rotating). This goal was achieved using both experimental and numerical approaches. A computational fluid dynamic model (CFD) was developed and validated using the experimental data. Electrical resistance tomography (ERT) was employed to measure the gas holdup. New equivalent impeller speed and diameter were defined and two novel correlations for the Power number and Reynolds number were proposed and successfully validated at different operating conditions. Additionally, new dimensionless correlations for the ratio of the gassed to un-gassed power consumption and the aerated power number as a function of the flow number, Froude number, and Reynolds number were developed and successfully tested for different coaxial mixing configurations.