In this study the performance of a forced convection
mixed-mode solar grain dryer integrated with a preheater was
evaluated. The type of grains used in the experiment were 72
freshly harvested maize cobs with a total mass of 17 kg. The
experiment was conducted at various airflow speeds and preheater
temperatures ranging from 0.5 m/s to 2 m/s and 30 ℃ to 40 ℃,
respectively. The aim of the study was to improve the performance
of an existing indirect solar dryer which was converted to a
mixed-mode solar dryer. The initial thermal efficiency of the
indirect solar dryer before modification was 36 %. The results
from the experiment indicated a maximum thermal efficiency of
58.8 % with a corresponding drying rate of 0.0438 kg/hr. The
minimum thermal efficiency for the mixed-mode solar grain dryer
system was 47.7 %, with a corresponding drying rate of 0.0356
kg/hr. The fastest drying time of maize cobs was achieved in 4
hours and 34 minutes from an initial moisture content of 24.7 %
wb to 12.5 % wb. The findings show a significant improvement in
the dryer system's performance. This is a clear indication that
operating a solar dryer system in mixed-mode operation with
forced convection and the assistance of a preheater or backup
heater can significantly improve drying processes and increase
food preservation.
Development and performance evaluation of mixed-mode solar dryer with forced convection
