Infrared energy incident on the food material creates
charges in electronic, vibrational and rotational states at
atomic and molecular levels [58], without heating the
surrounding air. Absorption wavelengths of various food
components vary (watersugarslipidsproteins
unsaturated lipids) as summarized by Rosenthal
[90]. Drying of agricultural products mainly takes place in
the falling rate period, and the generated sensible heat and
mass transfer co-efficient are functions of infrared power.
A variant of the basic infrared drying system is the catalytic
infrared (CIR) drying technique as shown in Fig. 7. As the
CIR directly converts natural gas or propane to radiant
energy by an intermediate catalytic reaction, it is more
energy efficient than the typical infrared emitters that use
electricity. To continue with safe product drying temperatures
(around 80 C), periodic on and off operations were
required to control emitter temperatures (which were
recorded to go up to around 750 C, as in their study
conducted by [44] on onions).