Temperature discontinuity during steady state liquid evaporation

Abstract

The conditions existing at the interface of an evaporating liquid and its vapor have become controversial. This chapter reports the results of an experimental study that tries to resolve certain of the controversial points. During the evaporation of water, the measurements indicate that as the rate of evaporation is increased, the discontinuity in temperature is increased and at each evaporation rate, the temperature in the liquid is less than that in the vapor. The observed relation between the temperature in the liquid and that in the vapor is the opposite of that predicted by kinetic theory or by nonequilibrium thermodynamics. Also, because the observed relation between the temperature in the liquid and that in the vapor, when evaporation occurs, is the opposite of that required for the existence of an anomalous temperature profile, these results suggest that an anomalous temperature profile will not be observed for water. These observations are in conflict with the theoretical predictions and raise questions about their validity. To understand the reasons for the differences between the temperature discontinuity during evaporation at the interface of water and that of mercury requires further study. Because the theoretical approaches provided by kinetic theory and by nonequilibrium thermodynamics do not yield valid predictions of the temperature profile at the interface of an evaporating liquid, there is no theory available for predicting the rate of evaporation currently.