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Abstract

Energy requirements and effective moisture diffusivity for thin-layer drying of tomato slices in a hybrid solar dryer was studied. A batch of 1800g of tomato sliced in 10, 13, 15, 17 and 19mm thicknesses were dried using varying heated air temperatures (50, 55, 60, 65, and 70^oC) and air velocities (0.1, 0.5, 1.0, 1.5, and 2ms^-1). The experiment was conducted using the complete randomized design (CRD) layout. Minitab 17.0 statistical package was used for analysis of variance and energy model development. Results obtained show that the energy requirement for drying a batch of sliced tomato samples increased with increase in the slice thickness and decreased with increasing air temperature at constant air velocity. The maximum and minimum energy requirements were obtained at 160.35 and 8.42kJ respectively, which corresponds to the thickest sample (19mm) at 0.1ms^-1 and 50^oC; and the lowest slice thickness (10mm) at 2ms^-1 and 70^oC respectively. The total energy requirements contributed by air velocity, slice thickness and air temperature were 19.82, 38.77 and 40.21%, respectively. Energy model of the hybrid dryer was developed and validated with R²-values of 0.9875 and 0.9982, respectively. Moisture diffusivities values of 3.8712 x 10^-9 and 9.6341 x 10^-9m²s^-1 were obtained for the minimum and maximum energy requirements respectively with corresponding activation energy of 20.26 and 45.34kJmol^-1, respectively.