Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


An experimental dryer with a data acquisition system to analyze single-layer rice drying was built and tested. Data of moisture content and time were collected for long grain Labonnet variety rough rice representing on-farm conditions (35(DEGREES)C to 55(DEGREES)C; 30% to 70% RH; 0.13 to 0.33 m/s drying air velocity) and commercial conditions (55(DEGREES)C to 75(DEGREES)C; 30%; to 70% RH; 0.63 m/s drying air velocity). The initial moisture levels of the rice at these conditions were 28, 33 and 38% (dry basis). Four different drying models were evaluated for the single-layer rice drying data. The first two were based on the solution of the diffusion equation and the others were empirical. The first empirical model was of a quadratic form, while the second empirical model was developed in a form analogous to the diffusion equation and assumed a linear dependance of the drying constant on the moisture content, as the drying proceeds. The two-term exponential form of the diffusion model and the second empirical model were selected, and a generalized form was developed with the aid of non-linear regression techniques for the on-farm conditions. For the commercial drying conditions, the second empirical model was evaluated. The effect of drying conditions of the air (including temperature, relative humidity and velocity) on the drying rate was also investigated. The generalized models that were developed were next used to analyze a deep bed situation in rice drying. The observed experimental results from the deep bed study were compared to the simulated results. The models in general tended to underpredict the moisture content; however, the empirical model showed better results than the two-term exponential model. These models overpredicted the air temperature in the deep bed situation. The largest difference in predicted and observed temperature was found in the top layers of the deep bed. Recirculation of exhaust air was evaluated for a deep bed rice drying situation. It was observed that the energy required to dry the grain increased with an increase in the amount of exhaust air recycled into the system.