Mathematical Modeling of a Cross-Flow Rice Dryer with Grain Inverters

Industrial-scale cross-flow dryers are commonly equipped with grain inverters to improve the uniformity of drying across the column thickness. While a few mathematical models have been reported that include the operation of grain inverters, such models were rarely validated with experiments comprising grain inversions. In this study, a mathematical model was developed to evaluate the impact of grain inverters on the uniformity of grain moisture content (MC) across the column in cross-flow dryers. To improve the accuracy of model predictions, the impact of using two thin-layer drying equations, the Newton and modified Page equations, in the model was also investigated. An experimental setup was fabricated to simulate grain inversion, and drying experiments were performed to measure rice MC and air temperature across the column thickness, which were then compared with model-predicted values. When the modified Page equation was used in the model, the model predictions matched the experimental observations more closely than when using the Newton equation. The model successfully predicted grain and air properties when 0, 1, and 2 grain inversions were used; the root mean square error between predicted and measured values of rice MC and air temperature were within 0.1 to 0.2 percentage points and 1°C to 4°C, respectively. Grain inversions were shown to improve the uniformity of drying in rice kernels; in the tested drying conditions, a single grain inversion produced more uniform drying than two or more grain inversions in the column. The presented results demonstrate the usefulness of the developed model in investigating the role of grain inversion in cross-flow drying of rice. As such, the model could be readily used to improve dryer design, particularly the number and arrangement of grain inverters, and optimize rice drying operations. Keywords: Deep-bed drying, Grain inverters, Mathematical modeling, Reversed airflow, Thin-layer drying.