DEVELOPMENT OF A SOLAR AIDED CRIB FOR DRYING AND STORAGE OF MAIZE

Abstract

The aim of this study was to design, construct, evaluate and model the performance of solar aided structure for storage of freshly harvested maize (Zea mays) in a humid tropical climate. A crib with two drying chambers of size 600mm x 685mm x 1500mm with moisture emission chamber of 600mm x115mm x1500mm in-between was designed, constructed and evaluated in Oba kekere FUTA. The wooden crib has roof made of perspex which transmit the sun's energy into stored maize in the crib. The crib was raised at 50mm above the soil and wire netted against rodents. It has two doors for easy loading and off loading. Maize of 30.5% moisture content (wet basis) was stored. Moisture content of the maize was taken on weekly basis while relative humidity and temperature measurements were carried out on daily basis for a period of six months. Readings were taken at three positions {top, middle and bottom} in holes that were made in those positions but are covered up at the end of every reading. The ambient temperatures varied from 20.90C to 380C and also relative humidity varied from 41% to 91%. There were no incidences of moisture condensation within the crib. Experimental drying curves obtained were converted to the dimensionless moisture ratio which was later fitted to a number of semi theoretical models namely Newton, Handerson & Pabis, Page Logarithm, Two Term, Verma et al, Diffusion approach, Midili Kucuk, Wang and Smith. These semi-theoretical models are derived based on theoretical model (Fick’s second law) but are simplified and added with empirical coefficients to improve curve fitting. In the empirical models a direct relationship is derived between moisture content, drying time and the parameters associated with it. Selection of the best model was investigated by comparing the determination of coefficient (R2), reduced chi-square (χ2) and root mean square error (RMSE) between the experimental and predicted values. A new model of MR = 0.442783exp-0.008424t1.609297 + .550438exp-.0592283t1.609297 was developed which is a combination of the Page equation and the Two-term model. The results showed that the new model with (R2) = 0.999139, (χ2) =0.008554 and (RMSE) = 0.0000846 found best described the solar aided crib for drying and storage of maize under the conditions tested. The structure possessed adequate structural integrity and there was no grain deterioration by fungal invasion and insects attack during the storage period.