Effective diffusivity of jatropha grains and fruits

Abstract

This study aimed to assess the influence of volumetric shrinkage in determining the effective diffusion coefficient, and obtain the activation energy of jatropha grains and fruits subjected to drying under varying air conditions. Jatropha grains and fruits were used with moisture content of 0.50 and decimal dry basis 4.40 (db), respectively, dried temperatures of 45, 60, 75, 90, and 105°C, and drying air relative humidity of 14.5, 7.4, 3.8, 2.2, and 1.4% for fruits and 15.6, 7.4, 4.0, 1.8, and 1.2 % for grains. The volume of jatropha grains and fruits, considered spheroids, was obtained by measuring the three orthogonal axes during moisture content reduction, and volumetric shrinkage was assessed by reducing the equivalent radius with the drying process. It is concluded that the effective diffusion coefficient of jatropha grains and fruits increases with increasing air temperature; the inclusion of volumetric shrinkage promotes a better fit of the liquid diffusion model; and activation energy of Jatropha grains and fruits is similar but the inclusion of volumetric shrinkage practically did not change this parameter.