Development and Performance Evaluation of a Solar Dryer for Copra

Abstract

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 °C, 61-70 °C and 71-80 °C 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 (V 1, V 2, 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 °C, 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.