SELECTION OF MATHEMATICAL-MODELS FOR DRYING GRAIN IN THIN-LAYERS

Several mathematical models or equations are used to describe thin-layer drying of agricultural grains. These are distributed parameter models, lumped parameter models and thin-layer drying equations. The assumptions frequently used are temperature equilibrium and surface moisture content equilibrium. There is no general analysis on the limitations of the models or equations and assumptions. The present article summarizes the results of an attempt to clarify the limits of the different models and assumptions. The heat and mass transfer Biot numbers were used to give the ranges where the simplified models or assumptions can be used without any significant error to predict the drying time and drying curve. Temperature equilibrium and surface moisture content equilibrium can be assumed in predicting the drying time or the drying curve without any significant error when the mass transfer Biot number is larger than 1000 and the heat transfer Biot number is less than 1. This is acceptable for most agricultural grains under practical drying conditions. © 1993 Silsoe Research Institute.