On the rate of evaporation of water into a stream of dry air, humidified air and superheated steam, and the inversion temperature

The concept of inversion temperature was developed in order to assess the effectiveness of superheated steam as a drying agent when compared with dry or humid air above a given temperature. The inversion temperature can be defined in different ways, for different physical situations, thus leading to strong discrepancies between its reported numerical values. A clear understanding of such definitions and its consequences over the inversion temperature values is of major importance, as well as the way to estimate the inversion temperature of interest for a given practical evaporation process. Analytical expressions are proposed for some possible definitions of the inversion temperature. Special emphasis is devoted to the physical reasoning on the existence of the inversion temperature and how its value is affected by other variables such as humidity level, mass flow rate and geometry of the evaporative system.