Kinetics and mathematical modeling of drying of parboiled paddy in a packed bed dryer

Paddy, the major staple food source used in Sri Lanka is subjected to many thermal treatments before consuming since the moisture content of the paddy must be in a desirable level for milling and storage purposes. Drying characteristics of two types of parboiled paddy (“Nadu” & “Samba”) were investigated in a packed bed dryer. Drying experiments for both paddy types were carried out at three different hot air temperatures 35oC, 45oC and 55oC by keeping hot air flow velocity and bed height constant as 0.98 m/s and 0.15 m respectively. Experimental results were fitted to three thin layer drying models; Midilli et. al., Weibull et. al. and Page. Statistical indicator; Root mean square error (RMSE) showed Midilli et. al., Weibull et. al. models give better fit to the experimental values. The drying curves lie totally in the falling rate period since the drying rate is controlled by the moisture diffusion of bound water. Maximum drying rates and Effective moisture diffusivity values were determined for different temperatures. The Activation energies of “Nadu” and “Samba” calculated based on the Arrhenius equation are 16774 J/mol and 19611 J/mol respectively