In this paper we present a theoretical investigation on heat transfer in a liquid film flowing around a horizontal tube in non-saturation conditions. In fact, we completed the models of Parken and Fletcher [1] and Solan and Zfati [2] by an analysis of the stagnation region located at the top of the tube. Finally, the model developed is validated by a comparison between the numerical predictions and experimental data [3]. The results of this work will be used directly to model a horizontal-tube falling-film evaporator for water desalination [4].