Numerical investigation on Marangoni convection of binary fluids in a closed microcavity

Phase change can dramatically alter the interfacial temperature, resulting in surface tension gradients and consequently causing Marangoni convection. The numerical investigation on Marangoni convection of binary fluids in a closed microcavity is accomplished in this paper by using the volume of fluid (VOF) model with source terms added by user defined functions (UDF) due to mass transfer, with detailed velocity and temperature fields. For simple fluid, surface tension decreases with increasing temperature, resulting in thermal Marangoni convection that can drive the liquid leave from hot regions and leading to film dryout. For binary fluids, however, the Marangoni convection could also be caused by concentration gradients, resulting in greatly promoted backflow of the fluid. In particular, for self-rewetting fluids which have unique surface tension characteristics that increase with increasing temperature above a critical value, the Marangoni flow can drive the liquid flow towards hot regions, avoiding film dryout. The influence of non-condensable gas is also considered by providing detailed velocity fields near the contact region and it proves that non-condensable gas can negatively affect the heat and mass transfer.