Microwave drying of paddy: Drying kinetics and modelling

Paddy PR121 variety was dried using microwave at 2450 MHz. The effects of power level (180 - 450 W), air flow rate (3 - 7 m/s) and exposure time (4 - 12 s) for different bed thickness (3 - 6 cm) levels on the moisture content (16- 12%, wb) were analysed by means of response surface methodology. Box-Behnken design was used to develop combinations for the responses. Drying occurred almost under falling rate period. The average value of effective moisture diffusivity (D_eff) range between 0.1415 to 0.6580 10⁻⁹ m²/s. A prediction of the moisture ratio using Page model provided the best R², x² and RMSE in drying kinetics studies. It was concluded that a combination of higher power level and short exposure time or a low power level and a long exposure time might be employed to achieve good drying of paddy.