Transition between regimes of a vertical channel bubbly upflow due to bubble deformability

The effect of the deformability of viscous bubbles on the flow rate of bubbly upflow in a vertical channel is examined using direct numerical simulations. A sharp transition between two different flow regimes has been observed. At large bubble deformability, characterized by large Eotvos number (Eo), the flow rate is close to the single phase flow rate, with adjusted pressure gradient, and the bubbles are almost uniformly distributed in the middle of the channel. On the other hand, at low Eo the bubbles are concentrated near channel walls and flow rates are much smaller than the single phase flow. The transition from high flow rate to low flow rate occurs rather abruptly. It is found that the transition occurs when the less deformable bubbles enter the viscous sublayer due to the lateral lift force on the bubbles. This leads to an increase in the viscous dissipation near the wall which leads to a decrease in the flow rate. (C) 2013 AIP Publishing LLC.