DYNAMICS OF BUBBLE-GROWTH AND DETACHMENT FROM A NEEDLE

Several aspects of the growth and departure of bubbles from a submerge d needle are considered. A simple model shows the existence of two dif ferent growth regimes according to whether the gas flow rate into the bubble is smaller or greater than a critical value. These conclusions are refined by means of a boundary-integral potential-flow calculation that gives results in remarkable agreement with experiment. It is sho wn that bubbles growing in a liquid flowing parallel to the needle may detach with a considerably smaller radius than in a quiescent liquid. The study also demonstrates the critical role played by the gas flow resistance in the needle. A considerable control on the rate and size of bubble production can be achieved by a careful consideration of thi s parameter. The effect is particularly noticeable in the case of smal l bubbles, which are the most difficult ones to produce in practice.