A laboratory-scale hot air dryer used in the present study is
schematically shown in Fig. 1 (Luangmalawat et al., 2008). The
dryer consists of a drying chamber with dimensions of 0.52
0.52 0.52 m and was insulated with glass wool; the dryer can
be operated both with and without auxiliary far-infrared heater,
which was not used in this study. Wire-screen tray, with dimensions
of 0.28 0.33 m, was placed normally to the direction of airflow.
The drying temperature was controlled by a PID controller
with an accuracy of ±1 C. Drying experiments were conducted at
an air velocity of 0.6 m/s and a temperature of 80 C. Eighty percent
of exhaust air was recycled and mixed with fresh air prior
to passing through the heating unit (No. 2) and drying chamber.
A 800 g sample of freshly cooked rice was used in each experiment.
Each drying experiment was performed until the moisture
content of the cooked rice sample reached the desired moisture
content of 10% (d.b.). The moisture content of the sample was
determined by drying in hot air oven at 103 ± 1 C for 72 h (AACC,
1995).