1. Convection
• Simplest dehydration technique of particulate or sheet-form or pasty solids
• The drying medium (hot air) flowing over the surface of the product, then the evaporated moisture carried away by the drying medium
• Dryers in this group are also called direct dryers
2. Conduction
More appropriate for thin products or for very wet solids
Heat for evaporation is supplied through heated surfaces (stationary or moving) placed within the dryer
The thermal efficiency of conduction dryers is higher than convection dryers
Dryers in this groups are also called indirect dryers