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A new approach to thin film evaporation modeling

Akkuş, Yigit
Dursunkaya, Zafer
Heat pipes which use phase change heat transfer mechanism and can carry large amounts of heat, are preferred in the cooling of high heat dissipating electronic components due to the fact that they are self-operating devices with ease of manufacturing for different geometries and ability of performance in micro-gravity applications. Heat pipes having rectangular micro channels as wick structure are used in many studies because of the relative ease of developing analytical and numerical solutions to problems of fluid flow and heat transfer. Investigation and development of unidirectional steady evaporation models which are used to describe the evaporation from the extended meniscus of a rectangular micro channel and widely applied in the literature, are the main interests of the current study. The thin film region of the extended meniscus has the maximum evaporation rates due to its small thermal resistance and with the adsorbed region, they are known as the micro region. In the literature, solution of the governing equations is usually started from the contact line which is the intersection of the solid, liquid and vapor phases. However, systems subjected to high superheats, have excessively small film thickness values near the contact line so that the real shape of the contact line or film thickness distribution cannot be observed experimentally. Therefore, in the current study governing equations are solved starting from a point in the intrinsic meniscus region where disjoining pressure is negligible. Resulting film thickness distribution shows that near the contact line, film profile bends inward contrary to many studies in the literature in which film profiles approach asymptotically to a constant non-evaporating thickness. Furthermore, non evaporating film thickness at the contact line cannot be found a priori solving the interface shape.