Behavior of a single coherent gas bubble chain and surrounding liquid jet flow structure

The motion of a single nitrogen gas bubble chain and the structure of water flow field surrounding the chain were experimentally studied. We developed a bubble generator that can control both the bubble diameter and the generation frequency independently. Experimental conditions of bubble Reynolds number and bubble distance divided by bubble diameter were from 300 to 650 and from 6.5 to 300, respectively. We discuss the interaction effects on the motion of each bubble rising in a chain, as compared to the effects of a single rising bubble. The bubble trajectories and the surrounding water flow fields in the state of bubbles rising in a chain were investigated using a high-speed digital video camera and an analog single-lens-reflex camera. We observed two important physical phenomena. First, bubbles passed through a nearly identical path in the case of low frequency of bubble production. On the contrary, at a height of approximately 50 mm from the nozzle, the bubbles in the case of high frequency deviated and scattered from this path due to bubble–bubble interaction. Second, with higher bubble production frequency, coherent bubble chain and the characteristic structure of the surrounding water flow called “liquid jet” were observed near the nozzle. The direction of liquid jet flow differed from the bubble trajectory. We theoretically investigated the relation of coherent bubble chain and liquid jet by applying the conservation of liquid momentum.