Numerical Study Of Conjugated Heat Transfer In Evaporating Thin-films Near The Three-phase Interface

The evaporation and heat transfer near the three-phase interface, such as the edges of the phase heat equipment, bottom of the droplets, is very intense. The evaporating thin film widely exists near the three-phase interline connected to the adsorption film and intrinsic meniscus region. It obtains a very low thermal resistance and high heat transfer coefficient. The flow and heat transfer in the evaporating thin film is complex because of multiple physical field coupling. Therefore, the conjugated heat transfer in evaporating thin film and intrinsic meniscus is helpful to understand the heat and mass transfer characteristics of evaporating thin film and its contribution to the total heat transfer and enhance the thermal performance of phase-change heat transfer devices.A generalized conjugated heat transfer model is developed, with an augmented Young-Laplace equation and the kinetic theory, for the conjugated heat transfer in evaporating thin liquid film and intrinsic meniscus and the vapor flow. Considered the vapor transport, conjugated heat transfer in evaporating thin films in the closed microcavity and the evaporating droplet are studied. In this paper, we quantitatively study the thickness, evaporating mass flux and integrated heat transfer rate in the evaporating thin films and analyze its contribution to the total heat transfer. Furthermore, the factors to the conjugated heat transfer in the evaporating thin film, such as sizes, superheats and contact angles, are studied. The conclusions are as follows:(1) The interfacial temperature drops fast and a maximum evaporating mass flux exists in the thin film region.(2) With the decreasing size, the contribution of thin films to the total temperature drop and total heat transfer increases obviously such that the thin film region cannot be neglected.(3) With the increasing superheat, the contribution of thin films to the total heat transfer decreases. But the variation is quite small compared with the influence of sizes especially at the micron scale.(4) With the liquid wets better, the contact angle is smaller and the contribution of thin films to the total heat transfer increases. For superhydrophobic substrates, the contribution of thin films can be neglected.(5) Due to the vapor transport in the air, the evaporating mass flux of the droplet is smaller than that in the closed microcavity.