Drying kinetics, modeling and quality of quince slices in thin layer air impingement jet dryer
Quince is a nutritionally important fruit, which is not much appreciated for fresh consumption. Drying of quince is one of the methods which is suited for preserving it against deterioration. In this paper, an experimental investigation was conducted to study the drying kinetics, modeling and quality of quince slices in an air impingement dryer under different drying temperatures, air velocities and relative nozzle-to-product distance (H/D) values. The results indicated that increasing drying air temperature and velocity can reduce the drying time. In addition, the impact of drying temperature on the drying time was more significant than that of the air velocity. It was also observed that the maximum heat and mass transfer occurs at the H/D ratio of 4 as Reynolds number varies between 4000 and 7500. The effective moisture diffusivity of quince slices ranged from 3.04×10-10 to 7.85×10-10 m2/s and the activation energy of quince slices were 23.570, 24.825 and 33.430 kJ/mol at different velocities of air. Based on the results reported in this study, the Midilli et al. model provided the best fit to describe the experimental drying data of quince slices. Furthermore, the results showed that the rehydration ratio of dried slices increased as drying temperature and H/D ratio rose and dropped with increase of the air velocity. Also results of color change of dried samples demonstrated that drying temperature and air velocity significantly affected the overall color change of quince slices, while the interaction between drying temperature and air velocity beside main effect of H/D ratio did not show any statistically significant difference in color change of dried samples. From the point of view of the drying time, rehydration ratio and color change of the dried slices, the optimum drying conditions were proposed.
Keywords: air impingement jet dryer, drying kinetics, quince slices, rehydration ratio, color change.