Selection and evaluation of thin layer drying models for infrared radiative and convective drying of onion slices

The infrared radiative and convective drying of onion slices have been studied at different operating parameters of drying using mathematical models. Experiments were conducted using three levels of infrared radiation intensity, 2·65, 3·53, 4·42 W cm ^-2, air temperature, 35, 40, 45°C, and air velocity, 1·0, 1·25, 1.5 m s ^-1, resulting in 27 drying tests. Nine mathematical models (Newton, Page, modified Page, Henderson and Pabis, asymptotic, logistic, two-term exponential, geometric, and Wang and Singh) describing thin layer drying have been investigated. The results were compared to their goodness of fit in terms of coefficient of correlation, standard error and the mean square of the deviation χ ². The asymptotic regression model could satisfactorily describe the infrared radiative and convective drying of onion slices with values for the coefficient of correlation of 0·9995, standard error of 0·0064, and χ ² of 4·4×10 ^-5. Asymptotic regression was performed with every test of experiment. Multiple linear regression analysis were performed to relate the coefficient of asymptotic models with drying condition of infrared radiation intensity, air temperature and air velocity. The developed model could predict the moisture content with drying time within an error of 1·11%. These results were within the experimental uncertainty of 4·38%.