The effect of liquid co-flow on gas fractions, bubble velocities and chord lengths in bubbly flows. Part II: Asymmetric flow configurations

•Two different initially separated vertical bubbly flows interacting in a channel•Difference in aeration between the two sides often result in buoyancy driven flows•Liquid co-flow has an organizing effect on the global flow behavior•Repeating buoyancy driven vortex roll-up phenomena found for specific conditions•Operating map constructed to predict emerging buoyancy driven flow structures [Display omitted] This paper describes the effects of uniform and non-uniform liquid co-flow on the bubbly flow in a rectangular column (with two inlets) deliberately aerated unevenly. The two vertical bubbly streams, comprising uniform bubbles, started interacting downstream of the trailing edge of a splitter plate. This study quantifies the emergence of buoyancy driven flow patterns as a function of the degree of a-symmetric gas sparging and (non-)uniform liquid co-flow by using Bubble Image Velocimetry (BIV) and dual-tip optical fibre probes. Without liquid co-flow, small differences in the gas fraction of the left and right inlet had a large effect on the mixing pattern, whereas a liquid co-flow stabilized a homogeneous flow regime and the flow pattern was less sensitive to gas fraction differences. Void fractions, bubble velocities and chord lengths were measured at two fixed position in the flow channel, whereas BIV provided a global overview of the flow structures. A correlation was developed to predict (a-symmetric) operating conditions for which the gas fraction of the left and right inlet are balanced, such that the bubble motion is governed by advection and no buoyancy driven flow structures arise. The data obtained is highly valuable for CFD validation and development purposes.