Thin layer drying characteristics of rapeseed (Brassica napus L.)

This study was performed to determine the most appropriate thin layer drying model and the effective moisture diffusivity of rapeseed. The thin layer drying tests were conducted at three different combinations of drying air temperature levels of 40, 50, and 60 °C and relative humidity levels of 30, 45, and 60%. The thin layer drying characteristics of rapeseed were determined. The Page (1949) model was the most adequate model for describing the thin layer drying of rapeseed. Drying occurred in the falling rate period and the rate of moisture removal from rapeseed was governed by the rate of water diffusion to the surface of the seed. Effective moisture diffusivities were calculated based on the diffusion equation for a spherical shape using Fick’s second law. Effective moisture diffusivity during drying varied from 1.72 × 10−11 to 3.31 × 10−11 m2 s−1 over the temperature range. The dependence of moisture diffusivity on temperature was described by an Arrhenius-type equation. The activation energy for moisture diffusion during drying was 28.47 kJ mol−1.

Research highlights
► Thin layer drying tests were conducted on rapeseed at three temperatures and relative humidities.
► Drying characteristics were determined.
► The Page (1949) model was the best model for the drying of rapeseed.
► The rate of moisture loss was governed by the rate of water diffusion to the seed surface.
► The activation energy for moisture diffusion during drying was 28.47 kJ mol−1.