Experimental Observation of Bubbles Released in Horizontal Water Flow

To investigate the characteristics of the bubble which is exposed to the liquid cross flow, the method of ventilation was adopted and air was injected into the water flow. A water tunnel was used to provide uniform water flow with variable velocity magnitude. A high speed camera was used to record instantaneous bubble images. An image-processing code was developed to identify bubble profile and to calculate bubble parameters. The effects of water flow velocity and the flow rate of the injected air were considered. The results indicate that bubble size decreases as the water velocity increases; meanwhile, ellipsoidal bubble shape is transformed into rounded shape. The variation in the air flow rate leads to a slight change of bubble size as well the bubble shape. The bubble velocity fluctuates with the movement of the bubble, and the fluctuations are intensified as the water velocity decreases. As the balance between the forces exerted on the bubble is reached, an approximately linear relationship between the bubble velocity and the water flow velocity is proven. For a given bubble equivalent diameter, the bubble terminal velocity with the liquid cross flow is higher than that associated with stagnant water. For small Eötvös number, the consistency of the bubble aspect ratio in the cross flow and the stagnant water is manifested; however, large Eötvös number obtained here is beyond the range associated with the stagnant water, and the existing relationship is extended.