The moisture content distribution at the end of drying, when the mean bed moisture
content has reached 13.7% dry basis is shown in Fig. 8. The mixed-mode has two
drying fronts and this is indicated by the moisture content at the top and bottom of
the bed being lower than that in the middle. This gives a more uniform moisture
content distribution than the indirect-mode. The indirect-mode on the other hand,
has only one drying front with grain at the bottom drying faster than that at the
middle and top, a typical deep bed drying behaviour. The difference between the
maximum and minimum moisture content is about 5.89 and 12.31% for the mixedmode
and indirect-mode dryers, respectively.
The temperature of grain at the top of the bed is shown in Fig. 9. The heating of
the bed by direct radiation in the mixed-mode is responsible for the drying front at
the top of the bed. The grain temperature in the mixed-mode is higher than that in
the indirect-mode because evaporative cooling in the mixed-mode does not occur.
The effect of evaporative cooling in the indirect-mode dryer can be seen in Fig. 9
where the grain temperature is lower than the ambient temperature during the first
five hours of drying.