Drying is defined here as: producing a dried solid by removal of liquid by evaporation, through supply of heat. (Drying through mechanical forces, e.g. centrifuges, or by non-thermal processes, e.g. osmotic dehydration, is excluded, as is drying of materials other than solids, e.g. gases. However, processes which do not begin with a solid feed, e.g. spray drying, or generate heat indirectly, e.g. RF and microwave drying, are included).
Drying can be treated as a unit operation, or as part of material processing (product engineering). Drying is important for integration (process systems engineering).