ABSTRACT
Agricultural produce contains high amount of moisture which makes it susceptible to the activities of micro-organism. This often results in deterioration. In order to minimize this spoilage, farm produce must be dried to safe moisture levels that permit its storage for a period of time. Drying of agricultural produce is a process that is carried out in order to prevent post-harvest losses, extend the shelf life of farm produce and maintain nutritional value. There are several energy sources for drying of agricultural produce but solar energy provides a clean and reliable source of energy. Open sun drying and solar drying are two methods of harnessing solar energy for drying purposes. Solar drying offers an efficient and effective method of drying even though majority of the agricultural produce such as grains, spices, fruits and vegetables are dried under open sun. Drying these produce directly under the open sun has many drawbacks such as debris, rain, blowing wind, insect infestation, human and animal interference etc. which leads to contamination of the produce. By the use of solar dryers, such problems can be easily overcome. Thus, there is a need to make the solar dryers more efficient and cheaper. This study presents the development, fabrication and performance evaluation of a mixed-mode solar energy dryer for drying of agricultural produce. The test location was Benin City (Lat. 6.3°N and Long. 5.6°E), Nigeria. The dryer is made up of a solar collector, drying chamber, thermal storage unit and a blower. The development features the following; the incorporation of a sensible heat energy storage unit which is embedded in the solar collector and positioned directly beneath the absorber to absorb downward heat losses from the absorber, store and release same for an uninterrupted drying process, the inclusion of flat fins attached to the base of the flat plate absorber to increase its surface area and the rate of heat transfer to the heat storage medium. With a collector area of 0.63 m2 , the solar dryer is developed to use a combination of direct heat (through the transparent glass covering of the drying chamber) and indirect heat (solar collector) to dry agricultural produce. A 12 V DC, 3.5 amps blower was used to force air through the solar dryer. Plantain sliced in the form of chips (3 mm thick) was used as test sample. The test was performed in October and November 2018. For October, the test was carried out on the 11th, 12th , 15th, 17th, 19th, 22nd, 23rd, 25th and 30th days of the month. In November, the test was conducted on the 2nd, 6th, 7th, 14th, 15th and 16th days of the month. Temperature and relative humidity were v recorded at different locations on the solar dryer at 30 minutes interval during the period of drying which occurred between 9am and 5pm.
