Thin-layer Drying of Parboiled Rice at Elevated Temperatures

Experiments were conducted to dry thin layers of long-grain parboiled rice at air temperatures ranging from 38–158°C and relative humidities from 0.3–80%. A series solution of the diffusion equation, considering long-grain rice as infinite cylinder, was used to express the moisture ratio. During thin-layer drying experiments it was necessary to develop a computational method to determine the relative humidity of air above 100°C without the use of wet bulb temperature measurements. An empirical exponential expression for moisture ratio gave the best fit to the drying data at all conditions. Parboiled rice was found to have higher values of effective diffusivity than raw rice.