The concept of solar air heating consists of a blackened absorber, well insulated at the lower and side with a transparent cover to allow solar radiation and block the infrared radiation. If any fluid is passed over/below or both side of the absorber, the fluid gets heated when exposed to solar radiation (fig. 1). The energy balance equations for transparent cover, absorber and flowing air can be written as

«gl+ hp-g(Tp Tg) — hg-a(Tg — Ta) (1)

Tg ap 1 — hp-g(Tp-Tg) + hp-b(Tp-Tb) + hp-f(Tp-Tf) (2)

The installed solar system is a roof-integrated type (plate I). For the installation of the solar system, a south facing asbestos roof was constructed at the site. The corrugated aluminium sheet was used as absorber by coating a solar selective paint. The glass wool insulation having a thickness of 65 — mm was packed beneath and sides of the absorber plate to suppress the heat losses. With some height above the absorber plate, 4-mm solar toughened glass was mounted. Baffles were provided to increase the air fil-factor and to improve the efficiency. The fresh air is allowed to pass through the gap between the absorber plate and glass cover in a zig-zag manner. While air is flowing through the air channel in the device, heat is extracted form the absorber by the air, resulting in a temperature rise or, in other words, hot air is obtained. The hot air is sucked by a centrifugal blower (3HP capacity and flow rate of 9000 m3/h) through an insulated duct and it is uniformly distributed in the drier, where chilly is loaded.

The drier consists of ten perforated aluminium trolleys each having a holding capacity of 100 kg of fresh chillies (plate2). The inside of the drier is fully covered with aluminium sheets to increase the life of the system and for hygienic processing. Two axial flow fans (2 HP each) having a volume flow rate of 20000m3/h were provided inside the drier for the uniform circulation and re-circulation of hot air. The hot air is made to pass through the chillies loaded in the drier and it draws moisture from the product and the warm moist air escapes through the dampers provided. The provision has been made to adjust the volume flow of air through the exhaust damper.