Wheat drying kinetics. Diffusivities for sphere and ellipsoid by finite elements

Abstract

A two-dimensional finite element model was used to analyze isothermal thin layer drying of wheat representing the grains as axisymmetric ellipsoids. The effective diffusion coefficient was estimated by minimizing the sum of squares of the residuals between numerically predicted and experimental moistures. Estimations done for drying air temperatures of 35°C, 50°C, 60°C and 70°C and initial grain moistures of 0.2694, 0.2396, 0.2133 and 0.1891 d.b., were correlated by means of Arrhenius-type functions. These correlations were compared to those previously obtained with the same data by assuming grains as spheres. The results, all in the order of 10 −11 m 2/ s , indicated that the diffusion coefficients found for ellipsoidal geometry were some 9–13% lower than the values fitted for spheres. The ratio of diffusivities for ellipsoids to those for spheres was in the order of the wheat sphericity. However, further theoretical and experimental studies are required to verify this observation.