Visual experiments on bubble growth and detachment at the tip of a capillary tube in stagnant liquid

The bubble growth and detachment at the tip of a capillary tube in stagnant fluid was experimentally investigated by using a high-speed visual system. The visualization experimental results show that the growth of the bubble experiences three typical stages: Initial growth, speedup growth, and speed-down growth accompanying with varying contact angles. The contact angle decreases with the bubble growth to reach near 50 degree and then increases quickly to reach near 140 degree accompanying with the detachment of the bubble from the neck of liquid. The detachment diameter of the bubble increases while the detachment period decreases with an increase in the internal diameter of the capillary tube and the gas flow rate. The volume of gas injection chamber has little influence on the bubble detachment diameter while the detachment period increases with increasing volume of the gas injection chamber.