Intermittent transition from bubbling to jetting regime in gas-liquid two phase flows

Abstract

The transition from bubbling to jetting regime in nitrogen-water system was studied experimentally. The gas was introduced into a pool of stagnant liquid through a single orifice plate above a gas chamber. Two quantities were measured: pressure fluctuations in the gas chamber and velocity of liquid circulations near the orifice. Individual bubbles were formed at low gas flow rates (bubbling regime) while a continuous jet of gas was formed at high rates (jetting regime). The transition from bubbling to jetting regime (transition regime) displayed intermittent character. Jetting bursts of various length appeared at random in originally periodic pressure signal. The distribution of bubbling portion in the pressure signal was hyperbolical with exponent −1.33 indicating type III intermittency. Similar characteristic time scales were found in power spectra of both signals. 1/ f noise was revealed in the velocity spectrum. This kind of noise usually accompanies intermittent transitions. These results implied that liquid circulations with 1/ f noise induced by bubbles affected the bubble dynamics itself as a feed-back and caused the intermittent regime transition. The point of the regime transition was indicated by a sudden drop of Kolmogorov entropy, correlation dimension of the attractor, and Mann-Whitney statistic calculated from pressure signal. An explanation for this drop is suggested on the base of combination of properties of two attractors coexisting/competing within the intermittency range.