Numerical and experimental study of the evaporation by mixed convection of a liquid film falling inside a vertical pipe

This article deals with a study of the evaporation by mixed convection of a water film falling along the internal wall of a vertical cylinder. The external wall is subjected to a constant uniform heat flux density. Transfers in the liquid and the vapor phases are described by classical equations of falling film and mixed convection. Their discretization by an implicit finite difference method provides systems of algebraical equations, which are solved by Thomas and Gauss algorithms. Exchanges in the liquid and the vapor phases are analyzed numerically for binary liquid film (water-ethanol or water-ethylene glycol) and experimentally for a water film. Numerical results show that the film thickness and its composition influence heat transfer. Measurements of wall and vapour phase temperatures provide experimental estimation of Nusselt numbers. The effect of such parameters as the liquid rate, the inlet air velocity and the wall heat flux density on the transfers is discussed.