The performance of a new prototype flat-bed grain dryer designed for experimental research was evaluated using yellow dent maize grain of two hybrids ("Clint" and "Raissa" which are hard and soft, respectively) in three separate experiments. In experiment I, grain samples at three initial moisture contents (approx. 20, 25 and 30% w.b.) were dried at three air temperatures (58, 80 and 110°C). Dryer performance parameters such as drying time, drying rate, capacity, efficiencies and energy consumption were determined and the dried grain quality attributes were also evaluated. A thin layer drying model for predicting dried grain moisture ratio was proposed. In experiments II and III, grain samples were dried at 80°C air temperature from 25% to 14.5% moisture content, cooled or tempered before assessment of grain quality attributes. Overall, the dryer performance was good in terms of its operation and effects on quality of dried grain. Both dryer operational performance and dried grain physico-mechanical properties were affected by drying air temperature, grain initial moisture content, and the post-drying treatments. Low initial grain moisture content and high drying temperatures increased dryer capacity and reduced total energy consumption for drying. However, both high drying air temperature and high initial grain moisture content increased the incidence of grain damage. Slow cooling and/or tempering of the dried grain increased grain bulk density and reduced breakage susceptibility, especially when cooled or tempered in an airtight and well insulated container. However, these two post-drying treatments did not affect grain hardness significantly. Finally, a conceptual model for evaluating and optimising the performance of mechanical grain dryer is proposed.
Publication arising from this thesis – Performance Evaluation of a Prototype Flat-bed Grain Dryer and Drying Characteristics of Soft and Hard Maize Hybrids can be viewed in the print copy held at the Library.