The convective hot air drying of Lactuca sativa slices

Abstract

ABSTRACTThe storage of fresh agricultural products is not easy because of its high moisture. Dehydration is an efficient preservation method. The investigation of drying modeling and transfer characteristics are important for selecting operating conditions and equipment design. The drying behavior of Lactuca sativa slices, with the thickness of 2 mm, was investigated at 60.0–80.0°C and 0.60–1.04 m sec−1 velocity in a convective hot air drier. The mass transfer during the drying process was described using six thin drying models. The convective heat transfer coefficient α and mass transfer coefficient kH were finally calculated. The results showed that the drying process could be separated into three stages including accelerating rate, constant rate, and falling rate period, which was influenced by hot air temperature and velocity, and the Modified Page model agreed well with the experimental data. When the operating temperature was increased from 60.0°C to 80.0°C, α was found increased from 88.07 to 107.93 W·m−2·K−1, and kH increased from 46.32 × 10–3 to 68.04 × 10–3 kg·m−2·sec−1·ΔH−1. With the increase of air velocity from 0.60 to 1.04 m·sec−1, α was increased from 78.85 to 101.35 W·m−2·K−1, and kH was enhanced from 51.78 × 10–3 to 65.85 × 10–3 kg·m−2·sec−1·ΔH−1.