Unsteady film condensation underneath the inclined wall of a solar still desalination system

Transient interfacial heat and mass transfer is investigated for film-wise condensation underneath the inclined wall of a solar desalination system developing a fully coupled arbitrary Lagrangian-Eulerian interface tracking (ALE-IT) algorithm. Evolution of solitary and capillary waves shows significant effects on the condensation rate of a condensate falling film. The influence of wall length, wall inclination angle, wall-vapor temperature difference, and vapor temperature oscillation are determined on the interfacial instabilities to investigate the condensation characteristics of a solar desalination system. It is shown that the length of the wall does not affect the onset of interfacial instability. However, increasing the length of the wall can effectively enhance the total condensation rate as a result of film waviness. Among the studied parameters, the wall-vapor temperature difference has the highest effect on the average mass flux. Each ${10}^{°}C$ increment in the vapor temperature can increase mass flow rate from 17% to 27%. At wall-vapor diference of 50°C, the increment in frequency of interfacial temperature oscillation increases the condensation rate up to 11%. Furthermore, each $5^{°}$ decrease in inclination angle from the horizon can enhance the condensation rate between 3% to 8%.