Design, construction and evaluation of performance of solar dryer for drying fruit

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September 2015
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An indirect type solar dryer integrated with a charcoal burning stove that can be used for drying fruits was designed, constructed and evaluated. The study mainly tried to address the problem associated with the fact that solar dryers are efficiently operational only when there is sufficient solar energy. Hence, an additional means of supplying heat was included so that drying can be made continuous during the night time and in rainy seasons. The dryer mainly consists of a solar collector panel, drying chamber, chimney and a charcoal stove. The solar collector is made up of 5 mm thickness single layer glass, 2 mm black painted aluminum absorber plate and 3 mm fiber glass insulation which is enclosed in a casing made from wood. The drying chamber is made from plywood with 2 cm thickness. Galvanized metal sheet of 1 mm thickness was rolled and welded to make the chimney. The backup heater uses a stove commonly known as “Gyapa” stove to burn charcoal and supply heat to the drying chamber. The total cost of the dryer was estimated to be GhC 1047.00 (US$ 327.00*). Different tests were carried out in order to evaluate the performance of the dryer. No load test, i.e. test without keeping any material to be dried, was performed and it indicated temperature could rise up to 53.3 o C in the dryer. Average collector temperature recorded was 56.4 o C. In the evening, the dryer temperature was kept above the ambient and collector temperature by burning charcoal using the backup stove. As a result, after three hours of heat supply the drying temperature reached 50.8 o C. * 1 USD = 3.2 GhC (as of February 2015) v The dryer performance was also evaluated using pineapple and mango. For the different tests carried out the performance parameters used for evaluation included moisture content, drying rate and drying efficiency. The moisture content of pineapple and mango was reduced from 87 % and 85 % to 16 % and 13 %, respectively, within two to three days. When using only solar energy as a heat source, the drying rate for pineapple was found to be 23.7 g/h whereas for mango it was 15.5 g/h. These values were found to be 25.2 g/h and 18.4 g/h, for pineapple and mango, respectively, when solar drying was performed with the backup heater (heater used in the evening only). But a higher drying rate was obtained, 32.5 g/h for pineapple and 19.3 g/h for mango, when the backup heater was used with the solar energy during both the day time and in the evening. The collector efficiency was found to be 31.7 %. Drying efficiency was also found to be 9.7 %, 7.5 % and 8.7 % for solar drying, hybrid mode (backup heater used in the evening) and solar drying in hybrid mode ( backup heater used during day time and evening), respectively.
A thesis submitted to the Department of Agricultural Engineering, Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements for the degree of Master of Science in Bioengineering College of Engineering, 2015