Heat and mass transfer in the evaporating film of a molecular evaporator

The hydrodynamic conditions in the wiped-film on the evaporating cylinder of a molecular evaporator have a considerable effect on the distillation output and composition of outlet streams from the evaporator. In this study, selected parameters are investigated in the laminar and turbulent regimes in the film, depending on the evaporator's liquid load and temperature. Results show that in the case of a turbulent film without concentration and temperature gradients at the same temperature of the evaporating cylinder surface, a higher portion of the feed is evaporated at a lower content of the more volatile component in the distillate. The model studied shows that there are only small differences in the relative volatility as a measure of separation efficiency in the turbulent or laminar film on the evaporating cylinder. The qualitative agreement between experimental results and the results from the model proposed shows that the model describes well the phenomena that occur within the distillation space of the molecular evaporator. (C) 2002 Elsevier Science B.V. All rights reserved.