Effects of Nozzle Structure on Bubble Deformation and Coalescence in Quiescent Liquid

Abstract

Bubble coalescence is not conducive to the process intensification of mass transfer in the chemical engineering field. In the present work, the effects of nozzle structure on the coalescence of bubbles are experimentally investigated by two synchronized orthogonal high-speed cameras. The results show that the rectangular nozzle has the highest probability of bubble coalescence, while the triangular nozzle has the lowest. Besides, the ascending process of bubbles is divided into two stages, i.e., the inertia stage with periodic oscillation and the free stage with shapes deforming unpredictably. The height of the inertia stage is shown to be decreasing with the increasing gas flow rate, dropping from 40.88 mm at 300 sccm down to about 24.04 mm at 700 sccm (about 0.53 and 1.24 m/s in superficial gas velocities, respectively). Finally, the influence mechanism of bubble deformation on bubble coalescence was investigated. Bubble coalescence is highly related to the interfacial instability induced by the bubble surface oscillation.