Use of Gas Helicity as an Indicator to Evaluate Impeller Design and its Gas Holdup: Proof of Concept for the Intensification of Gas-Liquid Mixing

Abstract

The fundamental insights into the impact of impeller geometry on the gas helicity can help equipment suppliers to design more energy-efficient impellers while reducing the overall energy expenses of wastewater plants and aerobic fermenter. In this perspective, the proof of concept was developed using electrical resistance tomography and computational fluid dynamics (CFD) modelling. At a fixed speed ratio (central impeller rotational speed/ anchor rotational speed), the sign of gas helicity (+ or -) provides insights about the gas velocity direction and the degree of gas holdup in non-Newtonian fluid. The predicted gas holdup was within the range of experimental measurement. In this experiment, the carboxymethyl cellulose (1 wt% CMC) solution was used. It is a non-Newtonian fluid which obeys the power law model. The ASI impeller was the most energy-efficient impeller which generate reasonable aeration efficiency with negative helicity. The poor aeration efficiency of some novel impellers such as ASI Slanted and PBT Up-Down were attributed to the fluctuations in the gas helicity sign. The proof of concept shows that the local helicity analysis can be insightful to better understand gas-liquid mixing and further intensify gas dispersion. The lift force generated by these impellers can be useful for anaerobic digester.