Abstract:
A conveyor-belt dryer was developed using a combined
infrared and hot air heating system that can be used in
the drying of fruits and vegetables. The drying system having
two chambers was fitted with infrared radiation heaters and
through-flow hot air was provided from a convective heating
system. The system was designed to operate under either
infrared radiation and cold air (IR-CA) settings of 2000 W/
m2 with forced ambient air at 30 °C and air flow of 0.6 m/s or
combined infrared and hot air convection (IR-HA) dryer
setting with infrared intensity set at 2000 W/m2 and hot at
60 °C being blown through the dryer at a velocity of 0.6m/s or
hot air convection (HA) at an air temperature of 60 °C and air
flow velocity 0.6 m/s but without infrared heating. Apple
slices dried under the different dryer settings were evaluated
for quality and energy requirements. It was found that drying
of apple (Golden Delicious) slices took place in the falling rate
drying period and no constant rate period of drying was
observed under any of the test conditions. The IR-HA setting
was 57.5 and 39.1 % faster than IR-CA and HA setting,
respectively. Specific energy consumption was lower and
thermal efficiency was higher for the IR-HA setting when
compared to both IR-CA and HA settings. The rehydration
ratio, shrinkage and colour properties of apples dried under
IR-HA conditions were better than for either IR-CA or HA.
