Experimental investigation of coalescence behaviour of bubble pairs forming at capillary orifices submerged in bacterial suspension

Abstract

Coalescence behaviour of bubble pairs markedly affected methane bioconversion because methane is usually pumped into a bacterial suspension through an aeration system, forming bubbles at capillary orifices. In the present work, a bioreactor was developed to observe the coalescence behaviour of bubble pairs forming at capillary orifices submerged in bacterial suspension via a visualization experiment. The results indicated that in a bacterial suspension the inrush bubble number decreased and the inrush time shortened, but the contact time was prolonged and the maximum contact area increased compared to those in pure water. Moreover, with an increase in the gas flow rate, the maximum contact area decreased and the contact time shortened, while more trailing bubbles merged into the leading bubble. Furthermore, the increase in the centre distance was conducive to increasing the maximum contact area and prolonging the contact time but the bubble inrush was observed at a centre distance of 0.94 mm. In addition, the larger centre distance enhanced the oscillation amplitude and frequency of the aspect ratio, which had not significantly changed at different gas flow rates. The results of this study will contribute to the optimal design of an aeration system that enhances the performance of the bioreactor.

Flowrate effects on the lateral coalescence of two growing bubbles

“…In the absence of air injection, the bubble oscillation is driven by excess energy due to the reduction in the bubble's surface area and curvature. [10,19] The projection area (A) provides further insight into the flowrate effects on the post-coalescence oscillatory behaviours of the coalesced bubble.…”

“…They also observed a decrease in coalescence time with increasing flowrate. Guo et al [ 10 ] investigated the coalescence behaviours of two bubbles at capillaries in bacterial suspension and water. They reported that the ratio of bubble width and height ( W / H ) before coalescence fluctuates more prominently at high flowrates, whereas no significant difference in W / H after coalescence was observed.…”

“…After the neck has evolved, the coalesced bubble oscillates on the needles, primarily driven by the excess surface energy due to the reduced interfacial area. [10,19] In the absence of gas injection, Bournival et al [20] displayed the anti-phase oscillation of the bubble's projection area (A) in the transverse and longitudinal directions in Milli-Q water. The bubble expansion transversely is accompanied by the contraction longitudinally and vice versa.…”

Experimental investigation on dynamic behaviour of bubbles emerging from micro‐capillary orifice in a flow channel

“…Bubble is widespread in various industrial fields, such as refrigeration, sewage treatment, renewable energy, and national defence, [1][2][3][4] where its dynamic behaviour directly affects the mass transfer performance of the equipment and even its safety. [5][6][7][8] In general, bubble formation is influenced by many factors, including fluid physical property, [9][10][11][12] gas escaping hole characteristic, [13][14][15][16] gas flow rate, [17][18][19] liquid flow rate, [20][21][22] and so on, which is a complicated, non-linear, asymmetrical, and unstable process. [23][24][25] Therefore, it is of great theoretical significance to study the dynamic behaviour of bubble.…”