At 12 kPa, a higher drying rate was achieved using the hot-air
fluidized bed than with the superheated-steam fluidized bed.
With the use of superheated steam, the sample temperature is
equal to the boiling point of water during drying, whereas with the
use of hot air, the sample temperature is lower than the boiling
point of water (Tatemoto et al., 2005b). Therefore, the temperature
difference between the fluidized bed and the carrot sample is larger
in the hot-air fluidized bed than in the superheated steam fluidized
bed. As a result, the rate of heat transfer from the fluidized bed to
the carrot is larger in the hot-air fluidized bed than in the superheated
steam fluidized bed. With the use of superheated steam,
thermal radiation from the steam contributes to the convective
heat transfer. However, the effect on the drying rate is minor at the
low temperature used in this study. Therefore, the drying rate is
higher in the hot-air fluidized bed than in the superheated-steam
fluidized bed. The temperature at which inversion of the rate of
surface evaporation using hot air versus superheated steam drying
occurs has been reported to be 453 K, which is much higher than