THE EVAPORATION COEFFICIENT OF WATER - A REVIEW

Publications, from the last 60 years, on the evaporation coefficient o f water have been collated and the experimental methods, results and c onclusions 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 struc ture, molecular collision in the vapour phase and heat transfer limita tions in the liquid phase. Following an extensive discussion, it is co ncluded that molecular collision and heat transfer limitations can hav e 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 conclu de From this investigation that for pure water evaporating into a spac e containing only water vapour, the true evaporation coefficient is un ity under all conditions of pressure and temperature. (C) 1997 Elsevie r Science Ltd.