R. Abalone

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.

DRYING OF BIOLOGICAL PRODUCTS WITH SIGNIFICANT VOLUME VARIATION. EXPERIMENTAL AND MODELING RESULTS FOR POTATO DRYING.

ABSTRACT This work is devoted to the experimental investigation and theoretical modeling of biological products with high initial moisture content which implies significant volume contraction. Firstly, experimental equipment which was designed to continuously determine variations in the global moisture content and in the temperature of the sample is introduced. Furthermore, the equipment is controlled by a PC which records experimental information in real time. In particular, measurement of the radial and temporal distributions of moisture content and temperature during the drying process of the homogeneous porous media potato are given. The mean moisture content and temperature curves are also given.

DETERMINATION OF MASS DIFFUSIVITY COEFFICIENT OF SWEET POTATO

Abstract Using Luikovs heat and mass transfer equations and a finite element formulation, the drying process of an anisotropic biological product (sweet potato) was investigated. The model was used to determine the coefficients of heat and mass transfer, the mass diffusivity normal and parallel to the fibers of sweet potato samples. These parameters were estimated by minimizing the deviation of experimental data and numerical predictions. Laboratory experiments with three different configurations were conducted to measure the temperature and moisture content of sweet potato samples during drying. Numerical simulation showed good agreement with the measured values.

DRYING OF BIOLOGICAL PRODUCTS WITH HIGH WATER CONTENT IN SOLAR REGIME. APPLICATION TO THE POTATO DRYING.

ABSTRACT The experimental results on the drying of biological porous media (potato) are modeled using the Luikov equations, under simulate insolation conditions. The temperature of the environment was regulated, within the typical range corresponding to hot-temperature and rather wet climate (Argentinas Humid Pampa region). The comparison between measurements and calculations gave good agreement. The present study confirms independently the identification of several characteristic parameters of the product obtained under constant conditions in a previous work [1].