Bubble coalescence: Effect of bubble approach velocity and liquid viscosity. (29th September 2015)

• Record Type: Journal Article
• Authors: Orvalho, Sandra; Ruzicka, Marek C.; Olivieri, Giuseppe; Marzocchella, Antonio
• Is Part Of: Chemical engineering science. Volume 134(2015)
• Page Start: 205
• Page End: 216
• Publication Date: 2015-09-29
• Subjects: Bubble coalescence -- Bubble approach velocity -- Liquid viscosity -- Transition regime; Chemical engineering -- Periodicals; Génie chimique -- Périodiques; Chemical engineering; Periodicals; Electronic journals; 660
• DOI: 10.1016/j.ces.2015.04.053
• Languages: English
• ISSNs: 0009-2509

Abstract

Abstract: The goal of this study is to present new experimental data on the effect of the bubble approach velocity and liquid viscosity on pairwise bubble coalescence. Measurements were performed to investigate the dynamics of bubble coalescence under well-defined laboratory conditions. Air and pure aqueous solutions of alginate (no surfactants) were the phases. The bubbles were formed from two vertical capillaries, under constant flow conditions. The coalescence process was recorded with a fast video and then image analysed, to evaluate the bubble growth, bubble expansion rate, the first bubble touch, bubble contact time T, bubble coalescence efficiency E . Three control parameters were tested. The bubble size D on contact was set by the spacing between the capillaries ( D =1 and 1.5 mm). The bubble approach velocity V was controlled by the gas input ( V =0.031–39 mm/s). The liquid viscosity μ was adjusted by the alginate content ( μ =1.2–10.3 mPa s). It was found that the bubble contact time T monotonously increases with the liquid viscosity, passing through three stages: initial rise (low μ, coalescence), then jump (intermediate μ, transient region), and finally forming a plateau (high μ, non-coalescence). In the coalescent regime, the bubble contact time monotonously decreases with the bubble approach velocity obeying a power law, which for a typical 1 mm bubble reads: T ∼ V −0.85 . The difference in the bubble size did not change the coalescence pattern qualitatively, but only quantitatively in a modest manner. Graphical abstract: Highlights: Detailed experiments on pair-wise bubble coalescence dynamics. Bubble approach velocity is controlled. Simultaneous effect of approach speed, viscosity, bubble size. Coalescent and non-coalescent regime maps.