Effect of Marangoni forces on interfacial heat and mass transfer driven by surface cooling

A fully resolved numerical study was performed to investigate interfacial heat and mass transfer enhanced by the fully developed Rayleigh–Bénard–Marangoni instability in a relatively deep domain. The instability was triggered by evaporative cooling modelled by a constant surface heat flux. The latter allowed for temperature-induced variations in surface tension giving rise to Marangoni forces reinforcing the Rayleigh instability. Simulations were performed at a fixed Rayleigh number (Ra$_h$) and a variety of Marangoni numbers (Ma$_h$). In each simulation, scalar transport equations for heat and mass concentration at various Schmidt numbers (Sc=16−200) were solved simultaneously. Due to the fixed (warm) temperature prescribed at the bottom of the computational domain, large buoyant plumes emerged quasi-periodically both at the top and bottom. With increasing Marangoni number a decrease in the average convection cell size at the surface was observed, with a simultaneous improvement in near-surface mixing. The presence of high aspect ratio rectangular convection cell footprints was found to be characteristic for Marangoni-dominated flows. ... mehrDue to the promotion of interfacial mass transfer by Marangoni forces, the power in the scaling of the mass transfer velocity, K$_L$∝Sc$^{−n}$, was found to decrease from n = 0.50 at Ma$_h$ = 0 to ≈ 0.438 at Ma$_h$ = 13.21 × 10$^5$. Finally, the existence of a buoyancy-dominated and a Marangoni-dominated regime was investigated in the context of the interfacial heat and mass transfer scaling as a function of Ma$_h$ + εRa$_h$, where ε is a small number determined empirically.