Reverse process of superheated steam drying from condensation to evaporation

Abstract

For clarification of the mechanism of heat and mass transfer in the early stages of superheated steam drying which accompanies condensation and evaporation, an experiment in which a water surface was used as a dried material was conducted under atmospheric pressure. Temperature profiles for in both the gas phase and the liquid phase near the water surface and the liquid level were measured precisely. From the results, heat transfer rates at the water surface and the amount of steam condensed into water were determined; in addition, the relationship between these two was investigated both experimentally and theoretically. Furthermore, a characteristic curve of drying accompanying condensation and evaporation in the early stages of superheated steam drying was derived semi empirically. In this drying characteristic curve, there is a point at which neither condensation nor evaporation occurs. This is defined as the `reverse point'. Introduction of this reverse point, and the time ratio for condensation and evaporation during the early stages of superheated steam drying are clarified.