Abstract
Liquid layers evaporating under the influence of a gas shear flow presents a non-uniform distribution of the evaporation rate all along the interface. Being the evaporation an endothermic process, a thermal gradient along the interface is generated and thermo-capillary flows are induced. Hence, two opposite mechanisms regulate the movement of the interface: the shear stress of the gas that entrains the interface in the direction of the flow and the thermo-capillary stress that forces the interface to move against the flow direction. The composition of these mechanisms at the interface generates an unstable thermal patterning. The dynamic evolution of the patterning and the relative evaporation rate are strongly influenced by the flow rate of inert gas, the layer thickness and the liquid thermo-physical properties. The goal of the present work is to study numerically how the evaporation process is influenced by the above-mentioned mechanisms. The focus will be on the evolution of the thermal patterning at the interface and the assessment of the main factors influencing the computed evaporation rate.
Highlights
Thermal and/or solutal patterning of evaporating fluid layers is becoming an intriguing field of research for its promising applicability in many industrial applications, including the rapidly expanding domain of bio-technology [1] and tissue engineering [2]
If we focus our attention on the liquid layer, we deal with a horizontal thermal gradient that acts along the interface in the direction of the flow and a vertical one due to the general cooling of the interface that makes the layer sensitive to convective instabilities
The coupling between evaporation and thermo-capillary convection has a strong effect on the thermo-fluid-dynamic field of a liquid layer subject to a flow of inert gas
Summary
Thermal and/or solutal patterning of evaporating fluid layers is becoming an intriguing field of research for its promising applicability in many industrial applications, including the rapidly expanding domain of bio-technology [1] and tissue engineering [2]. S. Iorio mass transfer rate for fluid layers evaporating in presence of a flow of inert gas is still an open domain of investigation. As a matter of fact, at the interface of the evaporating layers, the gas flow induces an additional shear stress that couples with the thermo-capillary one induced by the evaporation process. This coupling can alter significantly the thermo-fluid-dynamic field at the interface, change the heat and mass transfer rate. The influence of the shear stress at the interface has been thoroughly studied in cavity flow problems, by neglecting phase change processes The role that these three effects-evaporation, thermo-capillarity and shear-stress could have, when acting contemporarily, remains not completely understood [3]. Focus will be given to the role that the evolution of the concentration boundary layer could have in determining the effective heat and mass transfer rate at the interface
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