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

Hii and Law - Solar Drying of Major Commodity Products
clear corrugated fibre-glass and absorbed by the black plastic heat absorber inside the
structure. Forced air was supplied to transfer the heat inside the curing compartment.
The stagnant air space between the transparent exterior and the heat absorber acted as
an insulation layer. The concrete slab and block foundation served as an additional heat
storage system.
In the shell design, the greenhouse structure was covered with clear corrugated fibre-glass
to form a large solar collector with an integrated gravel energy storage system
for night time usage. An auxiliary fan to circulate the air over the absorbers and portable
frames were used to support the tobacco racks. The gravel energy system was designed
to store excess solar energy. Air was heated by the black surfaces of the absorber panels
and gravel bed and it was then forced through the gravel and bottom air ducts by the fan.
Soil drainage pipes were installed at the base to distribute the airflow uniformly through
the gravel base.
Heat absorber
Clear fiberglass
Heat absorber
Drying racks
Drying racks
Drying racks
Perforated
Plenum
a. Air ducts b.
Figure 3.10. Green house solar dryer type a) load supporting wall design and b) shell
design (not to scale)
Results showed that the load supporting wall design was able to save 15-25% fuel as
compared to the conventional bulk curing barn. Average unit fuel consumption was estimated
at 1.30 lit LPG/ kg cured barn based on 856.8 kg of cured weight. In contrast,
the shell design showed better saving at 33% – 51% as compared to the commercial unit.
The savings in both designs can be largely attributed to the total utilization of the solar
energy, immediate plus storage, the thermal enclosure design, insulation and proper
energy management.
Soponronnarit (1995) cited a study that investigated a solar assisted curing barn of
1 ton fresh leaves capacity and measured 3.6 m x 3.6 m x 4.8 m in dimension. An array of
38.5 m2 flat plate solar heaters and a 6 m2 rock bed unit were also installed. Forced air
was supplied by two units of blower at 1.5 kW and 0.75 kW each. LPG was used as an
auxiliary fuel source in this system. It was found that average fuel saving of 28% was
possible and average thermal efficiency was estimated at 40.5%. LPG consumption of
Drying of Foods, Vegetables and Fruits 87