Two-dimensional simulation model of steady-state mixed-flow grain drying. Part 2. Experimental validation

A model of a mixed-flow grain dryer at steady state, described in a previous paper,(1) was used to simulate a laboratory-scale dryer in which all input conditions and the grain moisture, temperature and viability loss had been recorded at the discharge and, for most runs, at points in the grain bed. The model was used to calculate grain flow rate for the observed moisture reduction, and the air and grain conditions throughout the grain bed for 11 drying experiments. A unique feature of the model allows it to calculate two drying regimes, one for the grain which passes near the inlet ducts, the other for the grain flowing near the exhaust ducts. Although grain input was overestimated in all cases by the model, by a mean of 10.9%, the loss of viability was predicted with an absolute average error of only 3.1% points of germination. The model underpredicted the viability loss where it was small, but predicted the loss at 125 degrees C very accurately. The moisture difference between the two drying regimes was predicted well in one run and underpredicted in another, and the magnitude of the observed moisture difference between inlet side and outlet side, 0.08 dry basis, showed the importance of the phenomenon in mixed-flow dryers. Predicted air exhaust temperatures were higher than measured, but balances for energy and mass performed on the dryer suggest that heat losses were partly responsible. The model predicted that cross-flow elements of the bed resulted in rapid heating of the grain, showing that this aspect of mixed-flow dryers is important in achieving accurate calculation of viability loss. A simpler model of mixed-flow drying predicted the grain input within 6.1% but because it did not represent the intense heating near inlet ducts, its predictions of viability loss were very poor. (C) 1998 Silsoe Research Institute.