Modelling study of dielectric properties of seed to improve mathematical modelling for microwave-assisted hot-air drying

摘要

Dielectric properties of canola seeds, corn, paddy rice, soybean and wheat were studied to determine the dependence of dielectric properties on frequency, moisture content and density of powdered seeds. In this context, several tests were done to find the relationship between the dielectric properties of the seeds at different frequencies (0.6-3 GHz) and at different moisture contents. Experimental data were used to parameterize standard linear models to predict the dielectric constant and loss factor. The resulting models were used in the prediction of heat and mass transfer parameters in a microwave (MW) assisted hot-air dryer at operating conditions of air temperature of 65 degrees C, a MW power density of 0.3 W g(-1), and for an exposure time of 30 min. The predicted results were in good agreement with experimental results obtained under the studied drying conditions. Germination tests were performed before and after each drying test to study the effects of the adopted drying conditions on the selected seeds. The results showed that the germination rate decreased for soybean but not for corn seed. This may be due to the hardness of the corn seed compared to that of soybean and also due to the grain density, which is higher for corn than of soybean.