Solar Drying: Fundamentals,Applications and Innovations - National ...

Visavale - Principles, Classification and Selection of Solar Dryers
Figure 1.27. Features of a typical distributed-type
active solar energy dryer
(Ekechukwu and Norton, 1999)
Figure 1.28. A distributed-type active
solar dehydrator with partial air recirculation
(Ekechukwu and Norton,
1999)
Figure 1.29. A continuous-flow active grain dryer (Ekechukwu and Norton, 1999)
1.11.2. Direct-Type Active Solar-Energy Drying Systems
The direct-type active solar dryers are designed with an integrated solar energy collection
unit. Generally, three distinct designs of direct-type active solar dryers can be
identified viz., the absorption type, storage type and greenhouse dryers.
1.11.2.1. Absorption Dryers
The direct absorption dryer as the name suggests are designs of the direct-type active
dryers wherein the crops absorb the solar radiation directly. Typical practical design
for large-scale commercial forced-convection greenhouse dryer, are of the type of
solar kilns for timber drying (Figure 1.30), transparent roof solar brans as shown in Figure
1.31 and small scale force-convection dryers equipped with auxiliary heating in Figure
1.32. Typical designs include with the roof or wall of the dryer functioning as a collector
of the drying chamber. Figure 1.33 shows the greenhouse dryer designed by
Huang et. al (1981) with a semi-cylindrical structure made of a Tedlar coated clear corrugated
fibre-glass and an internal dry chamber of rotary or stationary drum with a
Drying of Foods, Vegetables and Fruits 27