TRANSPORT PROCESSES AND INTERFACIAL PHENOMENA IN AN EVAPORATING MENISCUS

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Abstract
The chemical potential of an extended meniscus on an inclined flat plate is a function of its temperature, curvature, film thickness and height above a reference level. The meniscus thickness profile, which is related to the stress field in the liquid, was used to measure the sensitivity of the meniscus to the non-equilibrium effects associated with evaporation/condensation. The thickness profiles of a completely wetting film of a 1,1,2-Trichlorotrifluoroethane were measured using microcomputer based image processing of interferometric images. The automated data acquisition procedures were used to achieve enhanced resolution and thereby a better understanding of the transport processes occurring in the contact line region. The interfacial properties of the system were initially evaluated in situ and then used to describe the transport processes associated with a heated meniscus. Consistent with theoretical models, the curvature increased very rapidly from a value of zero in the adsorbed film at the leading edge of the intrinsic meniscus to a high value and then decreased rapidly until a thickness of about 1 μm. Flow results from a disjoining pressure gradient in the thinner region below the maximum curvature and from a curvature gradient in the thicker portion. At a higher power input, the meniscus was found to oscillate and the differences between the “advanced” and “receded” meniscus states were measured and analyzed. The curvature profiles in these two states are significantly different. The study showed that change of phase heat transfer and fluid flow in thin films are strongly coupled because of their common dependence on the intermolecular force field and gravity.