SOLAR DRYER (INDIRECT)

Indirect Solar Dryers differ from direct dryers with respect to heat transfer and vapour removal. The crops in these indirect solar dryers are located in trays or shelves inside an opaque drying cabinet and a separate unit termed as solar collector is used for heating of the entering air into the cabinet. The heated air is allowed to flow through/over the wet crop that provides the heat for moisture evaporation by convective heat transfer between the hot air and the wet crop. Drying takes place due to the difference in moisture concentration between the drying air and the air in the vicinity of crop surface. The advantages of indirect solar drying are:

1. a) Offers a better control over drying and the product obtained is of better quality than sun drying.
2. b) Caramelization and localized heat damage do not occur as the crops are protected and opaque to direct radiation.
3. c) Can be operated at higher temperature, recommended for deep layer drying.
4. d) Highly recommended for photo‐sensitive crops.
5. e) Have inherent tendency towards greater efficiency than direct solar drying.

They are, however, relatively elaborate structures requiring more capital investment in equipment.