Mathematical Modelling of the Drying Characteristics of Milled Sorghum Residue

Abstract

During milling of cereal grains, bran which is separated from the starchy endosperm of the grain is a major by-product. In this study, milled sorghum residue was dried in a cabinet dryer under different conditions (temperature and air velocity). The obtained drying data were fitted into ten existing mathematical models and obtained the best model while, the effective moisture diffusivity and activation energy of the drying process was determined using Arrhenius type approach. The result shows that the initial moisture content obtained for the sorghum residue using standard oven drying method were 41.28 ± 0.33%, 49.52 ± 0.63 % and 47.06 ± 0.42 % on wet basis for the wet residue of variety A, B and C, respectively, at equilibrium point, the final moisture content of about 12.93 ± 0.14 – 14.31± 0.07 as temperature ranges from 40 oC to 70 oC and air velocity ranges from 0.8 m/s to 1.2 m/s. During the drying process, the drying rate falls more rapidly as it was initially high as a result of more moisture in the sorghum residue and the drying rate decreases slowly until reaching the reduced moisture content. The obtained values of effective moisture diffusivity (Deff) ranges between 9.89 x 10-10 and 22.21 x 10-10 m2/s, 9.45 x 10-10 and 20.62 x 10-10 m2/s and 8.56 x 10-10 and 20.76 x 10-10 m2/s for variety A, B and C, respectively. However, the result of the modelling shows that the drying characteristics of variety A and B of the sorghum residue can be predicted using Midilli et al. model while the drying behaviour of Variety C can be predicted using Hii et al. model.