Influence of airflow velocity on kinetics of convection apple drying

Abstract

The aim of this experiment was to investigate airflow velocity influence (0.64, 1.00, 1.50, 2.00, 2.50 and 2.75 m s −1) on the kinetics of convection drying of Jonagold apple, heat transfer and average effective diffusion coefficients. Drying was conducted in a convection tray drier at drying temperature of 60 °C using rectangle-shaped (20 × 20 × 5 mm) apple samples. Temperature changes of dried samples, as well as relative humidity and temperature of drying air were measured during the drying process. Rehydratation ratio was used as a parameter for the dried sample quality. Kinetic equations were estimated by using an exponential mathematical model. The results of calculations corresponded well with experimental data. Two well-defined falling rate periods and a very short constant rate period at lower air velocities were observed. With an increase of the airflow velocity an increase of heat transfer coefficient and effective diffusion coefficient was found. During rehydratation, about 72% of water removed by the drying process was returned.