Comparative Study of Reversal Flow during the Evaporation or Condensation of Water and Ethanol Film in a Vertical Channel

A comparative study of reversal flow is carried out to investigate the effect of thermal and mass buoyancy forces with evaporation or condensation along a vertical channel. The highlight is focused on the effects of phase change of two different liquid films having widely different properties, on heat and mass transfer rates in the channel. The evaporation occurs along isothermal and wetted walls. The induced laminar upward flow consists of a mixture of blowing air and vapour of water or ethanol. Various combinations of thermal and solutal boundary conditions (cooling and heating modes) are considered to investigate extensively their influence on the flow development. A two-dimensional steady state and elliptical flow model is used and the liquid film is assumed extremely thin. The governing equations of the model are solved by FVM and the velocity-pressure fields are treated with the SIMPLER algorithm. The results show that the buoyancy forces have a significant effect on the hydrodynamic, thermal and mass fields of both gas mixtures. In addition, the flow reversal is predicted with a relatively high temperature difference between the air-mixture and the wetted walls.