MSc

Copra is one of the major traditional products dried from fresh coconut
kernels. It contains about 65% oil. It is produced from various methods such
as direct sun drying, solar drying, and traditional smoke drying, indirect
drying, etc. The objective of making copra is to reduce the moisture content of
coconut kernel to a safe storage level and thereby prevent microbiological
attack and spoilage. It is also used to extract coconut oil. There are many solar
drying methods introduced and developed to meet the requirements of drying.
The quality of copra and its cake is influenced by the method of drying the
coconut kernel. Improperly dried copra gives rise to certain moulds, the most
harmful of which is the yellow green mould called Aspergillus flavus and
other aflatoxin related moulds. Aflatoxin is harmful both for man and animals.
Improper processing results in low oil yield. Proper post-harvest practices, as
well as proper drying and storage can increase the oil yield. Proper drying of
coconut results in copra with lower moisture content and lower incidence of
aflatoxins. Since Kerala is the region with high humidity and comparatively
low solar radiation, there are chances of uneven and uncontrolled drying of
copra. Hence, an attempt was made to develop an advanced forced convection
solar dryer. Evacuated tube collector was used to generate hot air and it was
used to dry coconuts. In the drying chamber, the basic function of solar dryer
is to heat air to a constant temperature which facilitates extraction of moisture
from copra kept inside an insulated drying chamber. The coconut meat is not
directly exposed to the sunlight which will retain the nutritive values. The
performance evaluation of the developed solar dryer was tested at KCAET,
Tavanur. The average energy produced by the solar evacuated tube collector in
dry day was 63668.80 kJ. Evacuated tube collector consisted of 30 borosilicate
glass tubes of 1500 mm length and the outer and inner diameters were 47 and
37 mm. The length of manifold is 2.5 m and its inner and outer diameters of
cylinder are 12.5 cm and 40 cm, respectively. A 24 gauge galvanized steel
sheet was used to fabricate the chamber of 75 x 75 x 50 cm. The thickness of

the galvanized iron sheets was 2 mm and it was completely insulated using
glass wool of thickness 12.5 mm. The height of the exhaust duct with 11 cm
diameter was 120 cm. The drying chamber and the solar evacuated tube
collector were connected by metal duct of 60 x 15 x 10 cm. The evacuated
tube collector setup was placed on a supporting stand fabricated out of 2 x 2
cm square tube having 2 mm thickness. The solar drying was performed at
full load condition using heated air at 50-60 ℃, 61-70 ℃ and 71-80 ℃ and by
using different blower velocities of 0.2 m.s-1, 0.5 m.s-1 and 0.8 m.s-1 with and
without glass wool insulation. The temperature was controlled by providing
required shade to the evacuated tubes and theblower was controlled by using a
regulator for getting various air velocities (V1, V2, and V3). Drying time,
moisture content, relative humidity inside chamber and temperature inside the
chamber were considered as the dependent variables. Statistical analysis
(ANOVA) was performed using Design Expert software (Trail version 7.0.0).
The optimized operating conditions of temperature, blower velocity and
insulation were found to be of 71-80 ℃, 0.8 m.s-1 and insulation with critical
thickness of 12.5 mm. Hence, the developed solar dryer operated at the
optimized condition yielded good quality copra. Microbiological analysis was
conducted for dried copra and it was found that the tested samples were
microbiologically safe for human consumption.