Hydrodynamic performance of the ASI impeller in an aerated bioreactor containing the biopolymer solution through tomography and CFD

Abstract

In this study, the performance of the ASI impeller, a new impeller designed in our research group, was assessed for the gas dispersion in the non-Newtonian fluids. The effects of volumetric gas flow rate, impeller speed, and fluid rheology on power drawn and mixing time were explored. The non-Newtonian fluids were xanthan gum solutions at different concentrations. These biopolymer solutions are pseudoplastic fluids with yield stress and their rheological behaviors were assessed using the Herschel–Bulkley model. The hydrodynamic performance of this new impeller was compared to performance of the pitched blade turbine and the Rushton impeller. The electrical resistance tomography (ERT) was employed to measure the mixing time and gas holdup. The Eulerian–Eulerian approach was employed to simulate the gas-liquid flow inside this bioreactor through computational fluid dynamics (CFD). The CFD model was successfully validated by comparing the measured gas holdup and impeller torque values to the simulation results. The data analysis indicated that the ASI exhibited minimal effect of the gassing on power consumption (36%) compared to the Rushton turbine (50%). Furthermore, the experimental and CFD results in regard to the mixing time, power consumption upon aeration, and flow field generated in the aerated reactor proved that the ASI impeller was more energy efficient compared to the pitched blade turbine and the Rushton impeller.