Momentum interaction in buoyancy-driven gas–liquid vertical channel flows

Drag coefficient correlations for bubbles in buoyancy-driven two-phase flows have generally been derived from data on low-viscosity media and within the bubbly flow regime. In a number of applications, e.g. evaporative crystallizers, there is a need to extend this correlation to higher viscosity flows and slug regimes. In this paper, the momentum interaction in gas–liquid vertical channel flow has been studied experimentally over a wide range of void fractions using a circulation loop facility where the buoyancy is the only driving force for liquid circulation. A model for the drag in gas–liquid buoyant flows has been developed, and is applicable for a wide range of viscosity and void fractions.