Design and Evaluation of Solar Grain Dryer with a Back-up Heater

The aim of the study was to design and construct a solar grain dryer integrated with a simple biomass burner using locally available materials. This was to address the limitations of the natural sun drying for example drying exposure, liability to pests and rodents, over - dependence on sun and escalated cost of mechanical dryers. This became beneficial especially in reducing po st - harvest losses as well as helping in the preservation of agricultural product. The dryer is composed of solar collector, drying chamber, back - up heater and airflow system. The design was based on the study area of Mau summit located in Nakuru County, Ke nya. The average ambient conditions were 26°C air temperature and 72% relative humidity with daily global solar radiation incident on horizontal surface of about 21.6 MJ / m 2 / day . A minimum of 3.77 m 2 solar collector area was required to dry a batch of 100 kg maize grain in 6 h with natural convection from the initial moisture content of 21% to final moisture content of 13% wet basis. A prototype dryer designed was fabricated with minimum collector are a of 0.6 m 2 and used in the experiment . Forced convection was employed to reduce drying time. The thermal efficiencies of the solar and solar assisted dryer were 39.9 and 57.7%, respectively. The back - up heating system improved the efficiency of the dryer by 17.8% and reduced drying time substantially