A TWO-LUMP DRYING MODEL FOR EVALUATING COMBINATION DRYING OF CORN

ROBERT EDWARD MULLER, Purdue University

Abstract

Since none of the grain models currently in existence consider the moisture gradient within the corn kernel, they cannot adequately analyze combination grain drying. Therefore, a least squares regression program was developed to fit experimental thin-layer drying tests to a two-lump mass transfer model which considers this gradient. Dryeration data and other thin-layer tests were used to validate this model. It was found to fit all data reasonably except at 302(DEGREES)F where drying rates were underpredicted. Equations for the heat transfer coefficient, grain spoilage, and specific heat of grain were also modified and a new function solution procedure was also developed.^ These equations plus an equilibrium moisture content equation, psychrometric equations, grain property equations, and airflow equations were used to develop a grain drying model using SLAM. The partial differential heat and mass transfer equations were discretized to reduce them to ordinary differential equations. The resulting equations were found to be too stiff for SLAM to integrate, even after dropping the heat transfer equations and assuming temperature equilibrium. Therefore, sub-routine DGEAR from the IMSL library was used for the integration. The resulting model was validated against the SUNDRY and CRSFLOW models.^ A simulation experiment was designed to compare energy consumption and drying energy costs for combination drying at various switch-over moisture contents between high and low temperature drying, for high temperature drying with fast cooling, for dryeration, and for low temperature drying in 1977 (a poor drying year) using Purdue Airport weather data. If generation, transmission, and thermal efficiencies are not considered, energy consumption continuously decreases as the switch-over moisture content increases. If these efficiencies are considered, dryeration uses the least energy, combination drying at 18 percent switch-over moisture content uses only slightly more, and low temperature drying uses the most. Drying energy costs are lowest for dryeration with combination drying at 24 percent switch-over moisture content being nearly equal and combination drying at 16 percent switch-over moisture content being the most expensive. ^

Degree

Ph.D.

Subject Area

Engineering, Agricultural

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