Mathematical models for intermittent drying of rice

This study aimed to adjust mathematical models to experimental values in function of the water content and study the effects of intermittent relations in drying of paddy grains in the efficiency of operation. Paddy grains produced in the southern region of Rio Grande do Sul were used. The samples with approximately 20% water content were dried under three intermittent relation conditions: 1:1, 1:2, 1:4. In all these conditions the same thermal procedures were utilized, gradual increase in air temperature 70, 90, 110 +/- 5 degrees C respectively, in the 1st, 2nd and 3rd hour. For the adjustments of the mathematical models, a non linear regression analysis through the Simplex and Quasi-Newton methods was carried out. The values of the parameters of the models being estimated in function of the temperature of the drying air. A comparison was carried out of the adjusted coefficient of determination (R-adjusted(2)), the relative mean error (P), the estimated mean error SE) and the distribution of residues. The results showed that the intermittent relation modifies the operating time and the hourly rate of drying of the rice grains and the Midilli model was the one which best represented the intermittent drying of paddy.