Influence of buoyancy on bubble formation at submerged orifices

Abstract

The present investigation is concerned with the experimental determination of the influence of buoyancy on bubble formation at submerged orifices. The formation of air bubbles in water is analysed under reduced gravity and under terrestrial conditions. The experimental program includes variations of volumetric gas flow rates and orifice diameters. Two different flow regimes are identified. In the region of We ≤ 8 no bubble detachment occurs under conditions of weightlessness. In this flow regime, buoyancy completely determines the bubble formation under terrestrial conditions. Formed bubbles start to detach from the orifice under microgravity conditions only for We ≤ 8. Under conditions of weightlessness, the bubble size is decreasing with a gradient that decreases as the Weber number increases. For the bubble formation without buoyancy, the experimental and theoretical results demonstrate that the bubble diameter is directly proportional to the orifice diameter. With increasing Weber numbers, the comparison of experimental results shows convergence of the size of bubbles detached under microgravity and under terrestrial conditions. Therefore, the influence of buoyancy on the size of formed bubbles is reduced with increasing Weber number.