A numerical study of buoyancy-Marangoni convection of volatile binary fluids in confined geometries

Abstract

A horizontal temperature gradient can cause a flow in a layer of liquid with a free surface via several different mechanisms. The most universal one is due to thermocapillary stresses that arise due to the temperature dependence of surface tension. For binary liquids, the flow can also be driven by solutocapillary stresses that arise due to the dependence of surface tension on the composition of the liquid. For some binary liquids, such as water-alcohol mixtures, solutocapillary stresses are primarily due to phase change (e.g., differential evaporation or condensation of the two components), and these two mechanisms can counteract each other. A recent experimental study (Li and Yoda, 2016) has demonstrated that the flow direction can be reversed by changing the amount of air present inside the experimental apparatus. To understand how the presence of air affects the interfacial stresses, we have developed and implemented numerically a comprehensive two-sided transport model, which accounts for transport of heat, mass, and momentum in both phases and phase change across the interface and is able to reproduce the experimental results. The detailed analysis of these results shows that air tends to suppress phase change and hence solutocapillary stresses. Removing the air enhances phase change, instead suppressing the variation in the interfacial temperature and hence thermocapillary stresses.