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

Hii and Law - Solar Drying of Major Commodity Products
solar collector had a V-corrugated absorption plat of two air passes and covered with
single glass. Total collector area measured 2.04 m 2 . The dimension of the drying chamber
measured 1.06 m x 0.66 m x 0.56 m and can be loaded with 38 kg of corn. Moisture
content reduction from 21% to 13% can be achieved in 4 hours. The range of drying air
temperature obtained was from 30°C to 45°C at ambient condition of 8.5°C to 20°C. The
solar collector efficiency can be raised by 3.25% and 11.11% by increasing the volumetric
air flow rate from 0.025 m 3 /s to 0.03 m 3 /s and 0.03 m 3 /s to 0.035 m 3 /s, respectively.
3.2.3. Cocoa
The solar dryers developed for cocoa drying falls under various categories of design
i.e. direct, indirect, tunnel and green house effect solar drying systems. Minka (1986)
re-ported no increase in drying rates as compared to sun drying. The solar dryers tested
were the marquee dryer, which consisted of a drying platform covered by transparent
structure and the solar cabinet dryer. Bonarparte et al. (1998) developed and tested direct
solar cabinet (13.5 kg/m 2 loading) and indirect solar dryers (40.4 kg/m 2 loading)
and observed temperature increment up to 20°C and 15°C above ambient recorded in
these dryers, respectively. Hii et al. (2006) reported no significant finding in product
quality between solar and sun dried cocoa beans as quality changes occurred in a rather
similar rate in both drying systems (20 kg per batch drying load). The solar dryer developed
measured 153 cm x 91.5 cm in area with perforation measured at 1 cm diameter
holes arranged in 2 cm square pitch.
A hybrid solar dryer that uses rocks (painted in black) as solar collectors was developed
in East New Britain (Hollywood et al., 1996) for 200 – 250 kg bean loading. The
drying system consists of two sections namely the solar collector (filled with 3.5 m3
rocks) and the drying chamber (Figure 3.4).
Sunlight
Clear roof
Drying chamber
Rocks (painted black)
Figure 3.4. The hybrid solar dryer developed in East New Britain
Drying period was recorded within 4 days and extended drying was recorded at
night due to the heat released from the rocks. Temperature increment was recorded at
10°C above ambient at night time. Despite overcast days, bed temperature still remained
5-7°C above ambient temperature. The dryer was tested at East New Britain area with
average annual rainfall of 2500 mm. It was not recommended to use this dryer at region
that has 3569 mm annual rainfall in order to have optimum drying condition. The cost of
the dryer was about USD 1140.
A different design was developed and tested by Fagunwa et al. (2009) that was
based on a solar collector and a thermal heat storage chamber (Figure 3.5). The chamber
80 Drying of Foods, Vegetables and Fruits