Effect of orifice size and bond number on bubble formation characteristics: A CFD study

Abstract

The volume of fluid with the continuum surface force (VOF-CSF) model has been used in the present numerical study to investigate bubble formation and shapes in a bubble column. The effects of orifice sizes ranging from 0.5-1.5mm on the bubble formation stages (i.e., expansion, elongation, and pinch-off), bubble contact angle, departure diameter, time, and shape of bubble are investigated under a constant inlet velocity (0.2m/s) boundary condition (BC). It is found that the initial formation of a bubble is dependent on the orifice diameter. Consequently, the formation of the bubble's hemispherical shape at the orifice is faster for a smaller orifice diameter than for a larger orifice diameter which forms a bigger bubble. A leading bubble requires a longer time to detach itself from an orifice in comparison to the next bubble (the second bubble), but interestingly the third bubble detaches much faster than the second. This model was also used to investigate the effect of the Bond number (Bos). An increase of the Bond number (Bos) from 0.047 to 0.16 speeds up the bubble pinch-off, but a further increase in the Bos (e.g. 0.17-0.47) slows it down. Based on the simulated cases used in this study, the findings demonstrate the capacity and accuracy of the CFD method in predicting bubble formation characteristics. The findings may be useful in the design of spargers for bubble column reactors.