The drying of onion slices in two types of hot-air convective dryers

Abstract

Drying experiments were carried out using two types of convective hot-air dryers such that the hot air passed perpendicularly through a thin layer of onion slices in one dryer while the air passed parallel to the thin layer in the second dryer. The drying air temperatures were 50, 60 or 70°C, while air velocity was set at 0.5, 1.0 or 2.0 m/s. The drying behavior of onion slices under the aforementioned experimental parameters was fitted using Newton, Henderson and Pabis, Page and Modified Page models. The results were compared for their goodness of fit in terms of coefficient of determination (R2) and standard error (SE). The Page model was the best in describing the drying behavior of onion slices when compared to the other models. The drying time in the case of the horizontal convective hot-air dryer in comparison with vertical convective hot-air dryer was considerably less while onion slices dried at higher temperatures generally had higher rehydration ratios. Key words: Convective, onion, drying, modeling, rehydration.