Design And Evaluation Of Solar Maize Grain Dryer With A Back-up Heater

A solar dryer integrated with a simple biomass burner was designed and constructed
with locally available materials to dry maize. The dryer was composed of solar
collector, drying chamber, back-up heater and airflow system all integrated together.
The back-up heater provided alternative heating during cloudy weather conditions or
at night when solar radiations were low. The dryer was designed based on climatic
conditions of Mau summit located in Nakuru County, Kenya. The average ambient
conditions were 26ºC air temperature and 72% relative humidity with daily global
solar radiation incident on horizontal surface of about 21.60MJ/m2/day. This study
describes the design considerations and results of calculations of design
parameters. A minimum of 3.77m2 solar collector area was required to dry a batch of
100kg maize grain in 6 hours under natural convection from the initial moisture
content of 21% to final moisture content of 13% wet basis. Using similarity laws a
dryer with collector area of 0.6m2 was fabricated and used in experimental drying
tests under varied heat source conditions namely; solar, biomass and a combination
of solar and biomass. Solar assisted dryer system efficiency was estimated at 57.7%
with average drying rate of 0.077kg/hr with back-up heating operation increasing
solar dryer efficiency by 17.8%.