Experimental Investigations of Rise Behavior of Monodispersed/Polydispersed Bubbly Flows in Quiescent Liquids

Abstract

The predictive capabilities of continuum CFD models to simulate large-scale dispersed gas−liquid flows depend on the closures used to estimate the interphase coupling forces. The present manuscript shows that different corrections that are applied to correct the drag force for multiple bubble systems lead to different predictions as the gas volume fraction is increased. In the present work, experimental investigations of monodispersed and polydispersed bubbles of different diameters (1.2 ≤ dB ≤ 7.5 mm) rising in quiescent water (0.19 ≤ Eo ≤ 8.72; log Mo = −10.5) at different gas volume fractions (0.01 < αG < 0.2) are reported. The bubble rise velocity of a single isolated bubble, a bubble rising in a single chain and bubbles rising in multiple chains were compared. The effect of bubble diameter and gas volume fraction on the fluctuations in bubble rise velocities of individual bubbles rising in multiple chains was also investigated. The rise velocities of monodispersed bubble swarms were found to increase with the increase in dB and αG. The number- and time-averaged bubble rise velocity and drag coefficient for monodispersed bubble swarms were investigated as a function of αG. The drag coefficients based on the slip velocity of the bubble swarms for αG < 0.1 were found to decrease with increase in αG and showed good agreement with the previous literature; but for αG > 0.1, the drag coefficient were found to be independent of αG. Further, the rise behavior of poly dispersed bubbles was also investigated.