Three-Dimensional Numerical Modeling of Convective Heat Transfer During Shallow-Depth Forced-Air Drying of Brown Rice Grains

We describe here a three-dimensional (3D) numerical study of the convective thermal transfer during forced-air drying of brown rice grains with the inclusion of moisture evaporation. Three levels of temperature were tested across a range from 40 to 60°C. The objective of the study was to determine the temperature distributions in the drying chamber as well as the surface and intra-kernel temperature gradients during convective drying of rice grains. The numerical model was based on the Navier-Stokes equation for fluid flow and the Fourier's equation for heat transfer. Results of the numerical solution showed that temperature distribution in the air and brown rice grains during the early minutes of drying were significantly influenced by the direction of flow of the heated air. Air gaps between grains and at the periphery of the drying chamber affected the rate and direction of airflow. The temperature history of the rice grains showed variations at different levels within the layers of grains. Moreover, the stream of heated air showed regions with airflows eight times greater than the inlet air velocity.