Modelagem, simulação e experimentação da secagem contínua e intermitente de sólidos elipsoidais. Estudo de caso: secagem de grãos de arroz em casca.

Abstract

Heat and mass diffusion are found in many processes of technological interest, including drying of agricultural products. Among the existing drying techniques, intermittent drying is notable for reducing the energy consumption during the process and improve final product quality. In the present work, are developed mathematical models to predict heat and mass diffusion during the continuous and intermittent drying of ellipsoidal solids. The analytical solution of the twodimensional diffusion equation written in cylindrical coordinates is obtained via Galerkin -based integral method considering constant diffusi on coeficient and, equilibrium and convective boundary conditions at the surface of the solid. The tempering period is included in the mathematical modeling and moisture and temperature distributions are simulated in this period. The methodology was applied to describe rough rice drying. Continuous and intermittent drying experiments of rough rice grains (BRSMG Conai variety) were performed in different experimental conditions of temperature (40, 50, 60 and 70ºC), number of pauses (1, 2 and 3) and tempering time (30, 60, 120, 180 and 240 min). The intermittent drying kinetics of rough rice grains are presented and compared with the continuous drying for analysis of the drying rate and time. Continuous and intermittent drying simulation of prolate ellipsoid solids, for different aspect ratio and Biot number are presented and discussed. Theoretical results of the moisture content of rough rice grains are compared to experimental results, in order, to estimate both mass diffusion coefficient and convective mass transfer coefficient. A good agreement was observed between the predicted and experimental results. It has been found that the tempering time and Biot number have influence on drying kinetics. It was also observed an increase in the mass diffusivity in the after tempering period, which may justify the reduction of the effective operation time.