Influence of elevated pressure on the stability of bubbly flows

The effect of elevated pressure on the stability of the homogeneous bubbly flow regime in a gas-liquid bubble column is examined. Experiments were performed in a 0.15 m diameter bubble column operated at pressures in the range 0.1-1.3 MPa with nitrogen as the gas phase and water as the liquid phase. The transition from homogeneous to heterogeneous flow regime was determined by two procedures. The first procedure involved visual examination of the swarm velocity vs gas velocity curve to determine the transition point. In the second procedure the transient pressure signals were monitored by high-frequency pressure transducers and the instability point determined by analysis of the chaotic features. The two major findings of the work were: (a) increased system pressure reduces the bubble swarm velocity of the homogeneous dispersion, (b) increased system pressure results in a significant increase in the gas holdup at the instability point. The stability theory of Batchelor (1988, J. Fluid Mech.193, 75-110) and Lammers and Biesheuvel (1996, J. Fluid Mech.328, 67-93) has been used to provide theoretical support to these observations