The evaporation coefficient of water: A review

Publications, from the last 60 years, on the evaporation coefficient of water have been collated and the experimental methods, results and conclusions from these investigations are discussed. Reported values of evaporation coefficient of water range from 0.1 to 1 and despite many attempts to explain this large variation the evaporation coefficient is sill a subject of dispute. Three explanations which have often been used to account for low evaporation coefficients are. molecular structure, molecular collision in the vapour phase and heat transfer limitations in the liquid phase. Following an extensive discussion, it is concluded that molecular collision and heat transfer limitations can have a considerable influence on experimental evaporation rates and thus apparent evaporation coefficients. However, it now seems unlikely that molecular structure has a major effect on this coefficient. We conclude From this investigation that for pure water evaporating into a space containing only water vapour, the true evaporation coefficient is unity under all conditions of pressure and temperature. (C) 1997 Elsevier Science Ltd.