Size effect of oscillating columns on mixing: A CFD study

Abstract

Abstract Computational Fluid Dynamics (CFD) simulations were performed to study the effect of the size of the column on mixing in an oscillating column. Volume of Fluid (VOF) method was employed to track the interface, and tracer simulations were carried out to estimate the mixing time. The fluid was assumed to be water, and the ratio of the height of the water in the column and the diameter of the column was equal to 1. The amplitude of the applied oscillation was kept constant at 0.25 cm, and the frequency was varied from 1 Hz to 20 Hz. Two cylindrical columns were considered in this work: one with a radius twice the benchmark geometry and the other with a radius half of it. The benchmark geometry was the cylindrical column with radius = 0.05 m, which was utilized in our previous work (Bale et al., 2017). It was observed that the mixing within an oscillating column was nonlinear with respect to the applied oscillation. The mixing time per unit volume was much smaller for the larger column, with similar power per unit mass applied to both the columns. The optimal condition to operate the two columns under consideration were reported. The numerical simulation results were corroborated by the stability chart determined theoretically by solving a series of Mathieu equation, contour plots through the column, and the snapshots of the free surface.