Drying Kinetics and Shrinkage Rate of Thin-Sliced Pears in Different Drying Stages

In this research, the effect of different parameters of a convective hot air dryer on the mass transfer coefficients of thin-sliced pears in different drying stages is analytically and experimentally investigated. According to the results, in the first stage of drying which begins from the initial moisture content (MC) of 87–57% in this study, the convective heat transfer coefficient, the inlet air temperature and the initial MC of the product had the highest influence on the mass transfer rate of the drying product. In the second drying stage (from 57 to 27% MC), the structure of internal pore of the fruit, the internal MC and the thickness of the cut layers are the most influencing parameters controlling the mass transfer coefficient of the product. In the third region of drying (from MC of 27% to the final MC), the inlet air temperature had the greatest effect on the rate of mass transfer from the product. In this region of drying, increasing the drying temperature from 50 to 60°C at an airflow velocity of 0.5 m/s, yielded increasing the effective diffusion coefficient from 1.19 × 10−7 to 4.09 × 10−7 m/s2. The results of this study showed that increasing the airflow rate in the third stage of drying reduces the effective mass transfer coefficient. The highest effective diffusion coefficient in the third region of drying for thin-sliced pears was obtained equal to 6.24 × 10−7 m/s2 for drying temperature of 80°C and airflow velocity of 0.5 m/s.