Air humidification by free convection in a vertical channel

The evaporation of a thin liquid film flowing down on the internal face of one plate of a vertical channel is studied. The wet plate is subjected to a uniform heat flux while the second plate is taken isothermal and impermeable. The governing equations in the liquid and in the gas regions with the boundary and interfacial conditions are solved using a marching fully implicit method. The results obtained for an air-water system show that the interfacial heat and mass transfers depend largely on the inlet liquid film conditions (inlet temperature and inlet mass flow rate) and the external heating flux. In particular, it is observed that the interfacial heat flux may be larger than the heat flux imposed on the wall. This study also shows the importance of taking into account the inertia terms in the liquid energy equation.

The evaporation, by natural convection, of a water film flowing down in a vertical channel is studied numerically in this work. One plate of the channel is subjected to a uniform heat flux and wetted by the liquid film. The other one is isothermal and impermeable. The effects of the characteristics of liquid on the interfacial heat and mass transfers are analyzed. It is observed that the interface heat flux may be higher than the imposed heat flux. For a high value of the inlet liquid temperature, the total evaporation rate increases as the inlet liquid mass flow rate increases.