Effect of shunting ratio on the size of bubbles generated from a submerged orifice under oscillatory air supply

The diameter of bubbles generated from submerged orifices is closely related to the air pressure, which consists of static and dynamic pressures. It has been proven that switching the air supply from a steady to oscillatory flow can improve the dynamic pressure and thus lead to smaller bubbles. To complement the control strategy for bubble size optimization, this study proposes an approach to enhance static pressure by introducing a Y-junction shunting configuration under an oscillatory air supply. A model of gas pressure as a function of the shunting ratio was developed and validated experimentally. A positive correlation was observed between the shunting ratio and static pressure. The bubble size first decreased and then increased as the shunting ratio increased from 0 to 3.0. The smallest bubbles were obtained at a shunting ratio of 1.5 with a diameter reduction of 26% compared with no shunting. By segregating the bubble formation process, the bubble diameter at detachment continuously decreases over the shunting ratio. However, the number of coalesced bubbles first decreased and then increased, and the underlying mechanism is discussed. The findings indicated that the shunting air supply could facilitate bubble size optimization when the shunting ratio was appropriately controlled.