A. Gastón

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.

Effect of drying conditions on the quality of IRGA 424 rice: Effects of drying on rice quality

BACKROUND The objective of this research was to investigate the effects of drying temperature (40, 50, and 60 °C), tempering time (40, 80, and 120 min), and initial moisture content at onset of tempering (15, 17, and 19% dry basis) on head rice yield, milled rice yield, and total processing time of IRGA 424 rice. RESULTS The most significant effects were the drying temperature and its interaction with initial moisture content at onset of tempering. The optimum conditions predicted to reach the highest total yield (74.1%) included drying at 46.6 °C, 49 min of tempering time, and initial moisture content at onset of tempering of 19%. To achieve the maximum value of whole grain yield (52.9%), drying at 40 °C, 40 min of tempering, and an initial moisture content of 19% at the initiation of tempering were required. Under these conditions, the grain reached a moisture content of 13% in 84 min. CONCLUSION Whole-grain rice yields may be maximized through the optimization of the drying process. This may result in a larger fraction of the crop entering the human food chain, enhancing the value of the crop, and resulting in a smaller fraction of broken grain, which commands a lower market value.