Design and Performance Evaluation of a Geothermal Dryer for Maize Drying
Abstract
Exploiting geothermal energy to dry crops needs a properly designed geothermal crop dryer that is sized to meet the drying requirements of the crops to be dried. This study designed and fabricated a geothermal maize dryer that was tested to determine the drying time required to drying maize grains to 13% moisture content at Menengai Geothermal Project site within Nakuru County, Kenya. The main components of the geothermal dryer comprised of a dryer cabinet, heat exchanger, and fan unit. Once the air used for maize drying was heated by the heat exchanger, the sized fan unit blew hot air across the maize grains. Geothermal water from a discharging well within the project site supplied the heat to the sized heat exchanger. The designed geothermal maize dryer cabinet had dimensions of 0.55m × 0.25m × 1m with 40kg drying capacity, a 0.035kW axial fan with a 0.035kW, and a heat exchanger with 86.8 W/m2K heat transfer rate. The experimental results of the designed geothermal dryer showed that increasing the drying air temperature and drying air velocity inside the dryer resulted in reducing the total drying time while increasing the grain layer depth resulted in increased drying time. Experimental results revealed that the shortest drying time required to reduce the moisture content of maize from 19.3% wb to 12.9% wb was 4 ½ hours, achieved using a drying air temperature of 45°C, a drying air velocity of 0.5m/s, and a grain layer depth of 0.15m. This is significantly lower than the average of 5 days it takes to dry maize in open-sun drying.
