ABSTRACT
The term vapor drying refers to a process of convective drying where the vapor of an organic solvent is used as the medium for heating the material to be dried and removal of the evaporated moisture. Because condensation of vapors offers much higher heat-transfer coeffi cients than forced convection of air, the process heat is transferred to the drying material more rapidly and uniformly, so that drying times are considerably reduced. Moreover, the use of a partial vacuum in the system increases the rate of moisture removal. A distinction should be made at this point from superheated steam (SHS) drying (Chapter 7) and airless drying (Chapter 8), where steam is used as the convective drying medium. Also, vapor drying differs from solvent (displacement) drying (Chapter 18), where moisture is displaced by the solvent in the liquid phase due to surface tension forces or diffusion in the water-solvent mixture, and evaporation is used only to regenerate the spent solvent.
