reached a temperature of close to 100 C after 3 min of heating
compared to about 5 min for 4000 W/m2. But the heating rate
less than 3000 W/m2 was very low. If fast heating is desired, it
is essential to use high IR intensity.
The IR drying tests showed much higher drying rates
throughout the course of drying than the hot air drying
(Fig. 3). Since infrared radiation directly penetrated into the banana
and did not heat the surrounding air as that in the hot air
drying, infrared drying rate was much higher than the hot air drying.
Therefore, the drying rate of the infrared radiation was
much higher than that obtained from the hot air drying.
The drying rates varied with the radiation intensity as expected.
In infrared drying tests, there was an absence of or
very brief appearance of a constant rate period. This could
be because of the quick drying on the surface of products at
high temperature. The hot air drying tests showed more of
a distinct immediate entrance into the falling rate period.
The sample weight reduction results also showed that the
IR drying was much faster than that in hot air drying
(Fig. 4). For example, the IR heating took 3.1 and 6.2 min