Surface Shear Near the Contact Line of a Binary Evaporating Curved Thin Film

摘要

A model for surface shear in the contact line region of a steady state two-component evaporating thin film in the shape of a meniscus is developed. A constant vapor pressure boundary condition at the liquid vapor interface is combined with experimental meniscus profile data to obtain temperature and composition profiles. The results are used to delineate the relative effects of meniscus shape, temperature, and composition on fluid flow toward the higher temperature in an evaporating meniscus. For the system analyzed, it is found that surface shear due to composition gradients and temperature gradients is the single most important contribution to flow in the evaporating, two-component capillary meniscus in the film thickness range 0.000001 m < or = 0.00001 m. The effect of concentration on the vapor pressure leads to a maximum evaporation rate at a thickness of approximately 6 micrometers for the conditions studied. Theoretical results are discussed in the light of experimental observations.