Performance Evaluation of a Prototype Solar Dryer against the Conventional Sun-drying System in Nigeria

Aims: The objective of this paper is to develop a rectangular solar dryer box in which grains are dried by direct radiation through the transparent walls and roof of the cabinet and by the heated air from the solar collector. The temperature development of the dryer is also evaluated.
Study Design: For the development of a rectangular solar dryer system and analysis of its performance against a conventional sun-drying system in the rural communities in Nigeria.
Place and Duration of Study: Department of Mathematical and Physical Sciences, College of Basic and Applied Sciences, Samuel Adegboyega University, Ogwa, Edo State, Nigeria; between July and December 2014.
Methodology: The dryer is made of wood with a box-like drying chamber with the top cover plate made of tempered glass of 5 mm. This is where the solar energy is trapped and channeled into the drying chamber. Air passing through the collector is heated. The collector consists of a glass cover plate, an absorber plate and insulator. A colorless glass of 5 mm thickness is used for the cover plate. It is 30 cm long and 15 cm wide. It traps heat from the sun and prevents it from escaping. It is placed 4 cm above the absorber plate, this collects solar radiation. The absorber plate is made of aluminum sheet painted black measuring 30 cm by 15 cm. It is placed below the cover plate to absorb incident solar radiation transmitted by the glass cover plate and heats the air passing between it and the cover plate.
Results: We evaluated the constructed solar dryer performance using 5kg of maize cobs. Savings in time were achieved as against open conventional sun drying, it took 2 days for the maize cobs to dry to a stabilized moisture content of 24.3 g from 30.3 g using the constructed passive solar dryer while it took 6 days to dry the same cobs to 25.4 g under the open conventional sun drying system.
Conclusion: The passive solar dryer dries grains faster than the open conventional system i.e. sunlight. Since the developed dryer does not use electricity, it can be used by farmers in rural communities. Physical observation showed that, the maize cobs in the dryer looked cleaner than those that were sun dried.