A visualized study of interfacial behavior of air-water two-phase flow in a rectangular Venturi channel

A visualized investigation was carried out on the effect of the diverging angle on the bubble motion and interfacial behavior in a Venturi-type bubble generator. It was found two or three large vortexes formed in the diverging section, resulting in strong reentrant jet flow in the front of the bubbles or slugs rushing out of the throat. The jet flow in return bumps into the ongoing bubbles or slugs, leading to strong interaction between the gas and liquid phases. The diverging angle has significant influence on the reentrant flow process and the performance of the bubble generator as well. Increasing the diverging angle results in the reentrant flow moving further forward to the upstream and intensifies the interaction between the two phases. As a consequence, the breakup or collapse of bubbles becomes more violent, whereby finer bubbles are generated. As such, the reentrant flow strongly links to the performance of the Venturi channel taken as a bubble generator, and that a moderate increase in the diverging angle can improve its performance without additional increase in flow resistance like that by increasing liquid flow rate. (C) 2018 The Authors. Published by Elsevier Ltd on behalf of The Chinese Society of Theoretical and Applied Mechanics.