Influence of gas density on the stability of homogeneous flow in bubble columns

Abstract

Stability analysis is used to show that an important parameter determining the stability of homogeneous bubbly flows in a bubble column is the Richardson-Zaki exponent n in the bubble swarm velocity relationship U_swarm = υ_∞(1- ε)ⁿ. Analysis of bubble swarm velocity shows that with increasing gas density the value of this exponent decreases; physically this means that increasing gas density results in reduced interaction between neighboring bubbles and, consequently, reduced chance of propagation of instabilities. This provides a rationalization of the experimental observation that the influence of increased gas density, ρG, is to delay the transition from homogeneous bubbly flow to churn-turbulent flow.