Abstract
This paper reviews thin-layer drying equations for grain. These equations assume temperature equilibrium /TE/ between the grain and the drying air and moisture content equilibrium /MCE/ between the grain surface and its surroundings. The applicability of the different equations is considered and demonstrated both TE and MCE in grain drying are applicable but only when certain requirements are met. TE exists when Bi/Lu ≥ 2000 and MCE exists when Bi/Lu ≥ 500. According to the results Bi/Lu= 500 is the lower limit for assuming TE or MCE without a significant error in estimating the drying time and drying curve. When Bi/Lu<500 the general theoretical model has to be used.

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