Formation of bubbles in a coflowing gas-liquid jet at high Reynolds numbers

Abstract

The physical mechanisms underlying bubble formation from a needle in a co-flowing liquid environment at high Reynolds numbers are studied in detail with the aid of experiments and boundary-integral numerical simulations. To determine the effect of gas inertia the experiments were carried out with air and helium. The influence of the injection system is elucidated by performing experiments using two different facilities, the first one ensures a constant gas flow-rate penetrating the bubbles while in the second one the gas is injected through a needle directly connected to a chamber whose pressure remains constant during the bubbling event. In the case of constant flow-rate injection conditions, the bubbling frequency has been shown to hardly depend on the gas density, however, in the case of constant pressure supply conditions, the bubble size strongly depends on the density of the gas through the pressure loss along the gas injection needle.