Numerical study of conjugated heat transfer in evaporating thin-films near the contact line

The study of the mechanics of evaporating thin-films is important for improving the performance of phase-change heat transfer equipment. Various factors, including the changing profile of the thin-film with superheating and the use of small-scale and one-dimensional higher-order nonlinear governing differential equations, create difficulties for the study of the conjugated heat transfer of the thin-film and its surrounding regions. In previous studies, models of the conjugated heat transfer are simplified. The shape of the evaporating thin-film is treated as fixed, or the constant substrate temperature (CST) thin-film model is used. In this paper, a full conjugated heat transfer model, including the evaporating thin-film, the near-solid substrate and the intrinsic liquid, is proposed to study the heat transfer characteristics in the contact line region in a micro channel or a micro groove. The results show that a temperature valley value exists on the surface of the solid substrate corresponding to the peak value of the heat flow rate in the thin-film. The apparent contact angle is smaller than that of the CST model. The CST model overestimates the peak and the total heat flow rate, especially when the thermal conductivity ks of the substrate is low. For convenience in engineering applications, two simplified conjugated models are developed and evaluated by the full model. For low ks substrates, the simplified models can be used directly. Changing the thickness of the substrates affects the relative errors only slightly.