Thin-layer infrared radiation drying of rough rice

Four mathematical models for use in describing the thin-layer infrared drying characteristics of rough rice were investigated. The models considered were the exponential model, Page model, a diffusion model based on a spherical grain shape, and an approximation of the diffusion model. Tests were conducted using four levels of radiation intensity, 0.167, 0.333, 0.500 and 0.625 W cm(-2): three levels of inlet air velocity, 0.3, 0.5, 0.7 m s(-1); and three levels of grain initial moisture content, 0.25, 0.35, and 0.47 decimal d.b. and two replications for each treatment, resulting in 72 drying tests. Stepwise multiple linear regression analyses were performed to relate the parameters of the drying models with the drying conditions. Drying parameters of three models were correlated with radiation intensity and inlet air velocity and found to be independent of initial moisture content. The diffusion model involved the effect of variable initial moisture content. Goodness of fit of the experimental data by these models is based on comparing the residuals of moisture and root mean square errors between the observed and predicted moisture ratios. The exponential model, Page model and approximate diffusion model were statistically similar. The Page model was most adequate in describing thin-layer infrared radiation drying of rough rice. Duncan's multiple range test indicated the diffusion model to be significantly different. (C) 1997 Silsoe Research Institute.