Drying characteristics of maize grain in solar bubble dryer

A newly designed solar bubble dryer was used to study the drying behavior of freshly harvested maize grain. The performance of the dryer was tested at sample loads of 10.87 kg/m(2) (thin layer), 16.3 kg/m(2) (medium layer), and 21.74 kg/m(2) (thick layer) under two mixing conditions, 2 and 3 hr intervals. BH-540 and BH-660 maize varieties at 22-29% (w.b.) moisture content were used. A temperature rise of about 30 degrees C was recorded in the dryer with respect to the ambient air. The required drying time was highly dependent on sample load. About 24 hr were required to dry the grain to 13% (w.b.) moisture in thin layer compared to 39 hr in thick layer. More frequent mixing of grain (2 hr interval) shortened the drying time by 5-17%. The thin layer experimental data were fitted to drying models and the goodness fit of each model was evaluated using R-2, sum square error, and root mean square error. The Verma et al. and diffusion approach models gave better prediction for both varieties and mixing conditions. Fick's second law and anomalous diffusion models were considered for effective diffusion (D-eff) calculation. The anomalous diffusion mechanism fitted the experimental data better than Fick's second law and showed a subdiffusive behavior (alpha < 1). Practical Applications In developing countries, there is a high percentage of postharvest loss of grains due to traditional/open sun drying method after maturity stage of the plant. Solar drying is a good option to reduce the loss and to produce good quality grains after harvesting. In this study, the performance of newly designed solar bubble dryer and a thin-layer drying mathematical modeling for freshly harvested maize grain is presented. This study will be useful not only for small holder farmers, but also for all agricultural cooperatives in giving a sustainable and low-cost grain drying technology. It will be important to produce safe grain products for consumers and for different food industries. In addition, it may be helpful in the design, modeling, and performance assessment of solar dryers and can be used as a reference for solar drying applications for grain crops.