MATHEMATICAL MODELLING OF MOMENTUM, HEAT AND MASS TRANSFER IN GRAINS STORED IN SILOS. PART II: MODEL APPLICATION

摘要

A 2D finite element momentum, heat and mass transfer model was applied to predict natural convection flows, temperature distribution and moisture migration in soybean stored in a cylindrical bin without aeration from autumn to spring for the weather conditions of Rosario, Argentina. The effect of the initial moisture content and temperature of the grain (13%w.b and 25, 20 and 15°C) on stora-bility conditions was evaluated. During winter, stronger natural convection flows developed for 25°C, promoting an average moisture migration of 0.4%w.b and average grain temperature decrease of 5°C at the bin bottom. For 20°C, these values reduced to 0.15%w.b and 3°C. For 15°C, safe conditions remained and moisture migration was negligible during winter, but in spring, solar radiation and natural convection increased the temperature of a boundary layer of 1.5 m width above 18°C. Interstitial equilibrium relative humidity remained below the threshold for mold development (ERH > 75%). During spring, natural convection increased as the initial grain storage temperature decreased. Permeability has the strongest effect on natural convection and a five fold increase of this parameter resulted in the development of spoilage areas in the upper part of the bin. Soybean and corn showed comparable moisture migration while for wheat was not significant.