The aim of this work was to adjust the liquid diffusion model to the wheat drying curves considering the shrinkage of the grains and to determine the diffusion coefficients under different air conditions. Rough rice with 0.32 (d.b.) moisture content was used in this experiment. The drying procedure was done under different controlled temperatures of 25 to 55 °C with the drying air relative humidity of 55 ± 1%. The shrinkage of the grains was determined by the ratio between the volume of each moisture content and the initial volume. Based on the results, it can be concluded that the liquid diffusion model represents the wheat drying kinetics satisfactorily for experimental conditions in this test, however, the shrinkage of grains was not considered. The diffusion coefficient increases with the increase of the air temperature, with values ranging between 8.6775 x 10-11 and 41.0977 x 10-11 m².s-1 for the strip of studied temperature. The variation of the diffusion coefficient with the temperature may be described by the Arrhenius expression, presenting an activation energy of liquid diffusion wheat of 42.00 kJ.mol-1.
diffusion coefficient; shrinkage; modeling; wheat grains
