DEEP-BED GRAIN DRYING - A REVIEW OF PARTICULAR THEORIES

Theories developed for explaining the drying phenomena in grain drying systems are referred to as particular grain drying theories. The obje ctives of this paper are to review various particular grain drying the ories and to suggest directions for future research in this area. Grai n drying models are classified as non-equilibrium, equilibrium, and lo garithmic type. Four non-equilibrium models (stationary bed, cross-, c oncurrent-, and counter-flow) were reviewed. Under low temperature and low airflow conditions, drying in a stationary deep-bed occurs at nea r equilibrium. The derivation of an equilibrium grain drying model and its necessary assumptions were discussed., Logarithmic models were de veloped and applied by many researchers mostly to low temperature dryi ng in stationary deep-beds. A semi-empirical thin-layer equation is co mmonly used in the reported grain drying models. The inclusion of this equation is an important factor, that determines the cognitive and pr actical values of a grain drying model. Due to this equation, the disc ussed models lack the capability of explaining the drying process by t he laws of diffusion and the mathematical theory of drying solids. The computer simulation of grain drying systems can provide information f or design and improvement of grain drying systems.