Numerical parametric study of the evaporation rate of a liquid under a shear gas flow: Experimental validation and the importance of confinement on the convection cells and the evaporation rate

Evaporation can cause instability due to cooling effects on the density and surface tension. This causes, respectively, Rayleigh and Marangoni instabilities. When these instabilities grow sufficiently, self-sustained convection occurs. This convection causes changes into the evaporation rate and heat transfer rate. This also could change the heat transfer via the evaporation rate and can be important for industrial applications. It is the purpose of this paper to investigate the relation that exists between the overall evaporation rate and a set of parameters: temperature, gas flow and liquid thickness. Three-dimensional numerical simulations have been performed for this purpose and the results have been validated by means of an experimental setup, on which the numerical geometry has been based, characterized by a liquid evaporating through an opening in a cover sheet under a shear gas flow. It is shown that the temperature and the gas flow increase the evaporation rate. More interestingly, a maximum is observable for the evaporation rate as function of the liquid thickness. The explanation for these phenomena are drawn from the 3D numerical simulations. It appears that the maximum evaporation rate as a function of the liquid thickness depends on the confinement of the convection cells by the cover sheet, being assisted by the gas flow.