Thermocapillary instabilities in bubbles undergoing heat and mass transfer

A gas bubble in an unbounded liquid medium undergoing heat and mass transfer deforms as the bubble surface expands or contracts. Thermocapillary instabilities on the surface of bubbles can lead to convective flow in the near-field of the bubble. If the evaporation-induced thermocapillary instability is large enough, the interfacial tension gradients can sustain the instability and lead to the emergence of localized zones of cooler temperatures, herein referred to as thermal islands. This work uses detailed finite element numerical simulations to accurately resolve the transport and fluid dynamics around the gas–liquid interface. The interaction between shape oscillations, heat and mass transfer, and the fluid flow around the bubble is analyzed. We establish a correlation between the tangential velocities and the temperature gradient along the interface, thus emphasizing the role of the thermocapillary effect. We show how heat transfer in one direction may lead to stability with suppression of the thermal islands, yet the system becomes unstable when the direction is reversed. A discussion on the effect of appropriate dimensionless parameters on the stability of the perturbations is also presented. This investigation provides new insight into the dynamic behavior of nonequilibrium bubbles undergoing heat and mass transfer. It has practical implications for precisely controlling the transfer at gas–liquid interfaces.