Volumetric heating, microwave drying

Use of superheated steam in direct dryers Increased use of indirect (conduction) heating Use of combined (or integrated) heat transfer modes Use of volumetric heating (microwave [MW]/radio-frequency [RF] fields) in specialized situations Use of two-stage (or multistage) dryers Use of intermittent heat transfer Use of novel combnstion technologies (e.g., pulse combustion for flash drying)... 

Thermal drying caused by the vaporization of the liquid results as heat is supplied to the wet feedstock. As noted earlier, heat may be supplied by convection (direct dryers), conduction (contact or indirect), radiation, or volumetrically by placing the wet material in a microwave or radio frequency (RF) electromagnetic field. Over 85% of industrial dryers are of the convection type, with hot air or direct combustion gases as the drying medium. Over 99% of the application involves removal of water. All modes except the dielectric (microwave and radio frequency) supply heat at the boundaries of the drying object so that the heat must then diffuse into the solid primarily by conduction. The liquid must travel to the boundary of the material before it is transported away by the carrier gas (or by application of vacuum for nonconvective dryers). 

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