The hydrodynamic characterization of an oval airlift open pond (AOP) in the air–water system

Abstract

In airlift systems, the difference in gas holdup (εg ) between the riser and the downcomer creates the driving force for liquid circulation. This feature can be an interesting approach to using an airlift pump instead of the conventional paddlewheels for simultaneous mixing between phases and supply of air to microalgae in the biomass culture ponds. Before any biomass cultivation, the hydrodynamic behavior of the system must be recognized. Therefore, cold model hydrodynamic characteristics in the air–water system of a novel oval airlift open pond (AOP) are presented by studying gas holdup and riser liquid velocity (U lr) at different ratios of baffle clearances from the top and bottom (h t /h b) in the AOP. The gas holdup is one of the key parameters to describe the performance of airlift systems, so the effect of riser superficial gas velocity (U gr), riser liquid velocity, and h t /h b ratios on gas holdup are investigated in this research. The results of this study indicate that superficial gas velocity, riser liquid velocity, and h t /h b ratio have a pronounced effect on the gas holdup. Moreover, due to the lack of gas holdup correlations in the AOP system, new empirical correlations have been developed to predict total gas holdup, riser gas holdup (εg r), and downcomer gas holdup (εg d) with satisfactory accuracy.