Drag coefficients of single bubbles under normal and micro gravity conditions

Simple but reliable correlations for a drag coefficient, Co, of single bubbles under a wide range of fluid properties, bubble diameter and acceleration of gravity were developed based on a balance of forces acting on a bubble in a stagnant liquid and available empirical correlations of terminal rising velocities of single bubbles. The proposed Ca consists of three equations, each of which corresponds to pure, slightly contaminated and contaminated systems. The effect of a frictional pressure gradient due to a liquid flow is also taken into account by introducing a concept of an effective body acceleration. Terminal rising velocities of single bubbles were calculated using the proposed Ca, and compared with measured data under the condition of 10(-2)<Eo<10(3), 10(-14)<M<10(7) and 10(-3)<Re<10(5) where Eo, M and Re are Eotvos, Morton and bubble Reynolds numbers, respectively. As a result, it was confirmed that the proposed C-D gives better predictions than available drag coefficient models.