A single-layer model for far-infrared radiation drying of onion slices

Three mathematical models were investigated for the description thin-layer far-infrared drying characteristics of fruits and vegetables. The models considered were the exponential model, the Page model, and an approximation of the diffusion model. Tests were conducted using three levels of far-infrared radiation intensities (0.50, 0.80 and 1.00 kW/kg of initial mass of onion), three initial thicknesses of onion slices (2, 4 and 6 mm), three air velocities (0.10, 0.20 and 0.35m/s) and three inlet air relative humidities (28.6, 36.8 and 43.1%), and with two replications for each treatment. Stepwise multiple linear regression analyses were performed to relate the parameters of the model with the drying conditions. The performance of these models is evaluated by comparing the coefficient of correlation (r(2)), the residuals of moisture ratios, and the root mean square errors between the observed and predicted moisture ratios. The Page model MR = exp(-kt(N)) was gave the best results in describing single-layer far-infrared radiation drying of onion. Drying parameter k of the Page model was correlated with radiation intensity, initial thickness, air velocity and air relative humidity, and N was found to be independent of the four drying conditions.