LOW-TEMPERATURE MOISTURE TRANSFER CHARACTERISTICS OF BARLEY - THIN-LAYER MODELS AND EQUILIBRIUM ISOTHERMS

Thin-layer drying experiments were conducted with barley in the lower temperature range of 3·9 to 19·6·C and for relative humidities between 36·6 and 86·6%, with initial moisture contents in the range 19-28% dry basis (d.b.). Several higher temperature experiments (24·5-49·2·C) were included for comparison with previous work. The well-established apparatus was modified to enable the automatic recording of all the sample weight data in still air. Very smooth drying curves were obtained. The data of sample weight, drying temperature and dew point temperature were recorded continuously. The drying process was terminated when the moisture content change in 24 h was less than 0·4% d.b. The final points were recorded as the dynamic equilibrium moisture content. The Newton model and diffusion model were both fitted to the data. The Arrhenius equation was used to describe the temperature effect in both cases. The diffusion model gave a better fit for the moisture content with a standard error of 0·149% d.b. as opposed to 0·501% d.b. for the Newton model. The effect of variable initial moisture content was described far more effectively by the diffusion model. The drying constant, K, in the Newton model was in broad agreement with previous work. The drying time employed had a large effect on the K value. Drying times in excess of 5 d were used throughout this work. Existing data on the equilibrium moisture content isotherms were compared with the dynamic equilibrium moisture contents observed in this work. The modified Chung-Pfost equation was fitted to the present data and previously unfitted data, and appropriate isotherms are recommended. © 1994 Silsoe Research Institute.