Abstract: The influences of vessel pressure， nozzle diameter and gas flow rate on bubble’s behavior， diameter and rising velocity were investigated through physical experiment. The results showed that the bubbles from larger diameter nozzle show flat shape and their shapes change obviously during their up-rising process under atmosphere pressure， while the bubbles show oval-shaped and their shapes are stable in up-rising process under larger pressure. Gas flow rate has small effect on the bubble’s diameter with large diameter nozzle under atmosphere pressure， but it can obviously increase the bubble’s diameter and pressure has little influence on bubble’s diameter from small nozzle. With low gas flow rate and high pressure， the small bubbles can be obtained from the larger diameter nozzle. The difference of bubble’s diameter with different flow rates in injecting gas with the large nozzle is small under 0.1~0.2MPa pressure， while the difference becomes large when the pressure is increased to 0.3~0.4MPa. Rising velocity of bubbles decreases with increase in pressure and the influence of pressure on bubble’s rising velocity is more obvious at large gas flow rate. The bubbles from the large nozzles usually have higher rising velocity. Under atmosphere， the gas flow rate has important effect on rising velocity of bubbles， but under pressure up to 0.4MPa， the nozzle diameter has more important effect on their velocity.

Key words: vessel, liquid, bottom injection, bubble behavior, vessel pressure, nozzle diameter, gas flow rate