Combined concentration and temperature-induced marangoni convection in a binary mixture

In binary and multi-component mixtures, surface-tension-driven flow, i.e., Marangoni convection, can arise from both concentration and temperature gradients at the liquid surface. Depending on the liquids, concentration effects can complement or oppose temperature effects, which is important for many areas of engineering interest, e.g., mixing, solidification, evaporation, and drying. This work experimentally investigates combined temperature and concentration-induced Marangoni convection for an ethanol-water binary mixture in an enclosed cell with heated and cooled walls. Velocity profiles are obtained using a photochromic dye technique, and concentration variation at the liquid surface is measured using an interferometric technique. The results indicate that concentration effects dominate at 50/50 and 80/20 ethanol-water volume percent mixtures, resulting in a large surface velocity in the opposite direction to the bulk flow. Concentration effects can be arrested by exposing the free liquid surface to non-condensable gas at atmospheric pressure.