Modelling of free bubble growth with Interface Capturing Computational Fluid Dynamics

This paper presents simulations of the growth of stationary and rising vapour bubbles in an extend pool of liquid using an Interface Capturing Computational Fluid Dynamics (CFD) methodology coupled with a method for simulating interfacial mass transfer at the vapour-liquid interface. The model enables mechanistic prediction of the local rate of phase change at the vapour-liquid interface and is applicable to realistic cases involving two-phase mixtures with large density ratios. The simulation methodology is based on the Volume of Fluid (VOF) representation of the flow, whereby an interfacial region in which mass transfer occurs is implicitly identified by a phase indicator, in this case the volume fraction of liquid, which varies from the value pertaining to the "bulk" liquid to the value of the bulk vapour. The novel methodology proposed here has been implemented using the Finite Volume framework and solution methods typical of "industrial" CFD practice embedded in the OpenFOAM CFD toolbox. Simulations are validated via comparison against experimental observations of spherical bubble growth in zero gravity and of the growth of a rising bubble in normal gravity. The validation cases represent a severe test for Interface Capturing methodologies due to large density ratios, the presence of strong interfacial evaporation and upward bubble rise motion. Agreement of simulation results with measurements available in the literature demonstrates that the methodology detailed herein is applicable to modelling bubble growth driven by phase-change in real fluids.