On the Characteristics of Thin-Layer Drying Models for Intermittent Drying of Rough Rice

In the present study, several drying experiments were carried out to investigate the drying behavior and the feasibility of using the intermittent drying method. Iranian rough rice with the initial moisture content (MC) of 17.65% (dry basis) was dried by a laboratory-scale dryer with an intermediate tempering stage at drying air temperatures of 40 degrees C, 50 degrees C, and 60 degrees C and air velocities of 2.2 and 3.2m/s. According to the experimental results, tempering stage greatly affected the drying performance. Besides, the drying rate was increased with drying temperature; however, the effect of the air velocity was negligible. Various thin-layer drying models were separately examined based on the statistical analysis in order to define the behavior of each drying stages namely pre-tempering and post-tempering. The results indicated that the Midilli and two-term models are the most appropriate models for the first and second drying stages, respectively. The constants and coefficients of these two models can be expressed as a polynomial function of the temperature and velocity of drying air. The parameter estimation procedure was employed in order to evaluate the effective moisture diffusivity.