Pistachio Nut (Ohadi Variety) Mass Transfer Simulation during Process of Drying Using Finite Element Method

Drying is an important operational step in pistachio processing. There is a decrease in moisture content of pistachio nuts from 56-57% (d.b.) to 5-6% during the drying process. Drying conditions affect the quality of dried pistachio nuts, therefore, this calls for an accurate description of the drying trend in the process. In this study finite element formulation and solution of diffusive moisture transfer equation was presented to improve the drying simulation of nut as an axisymmetric body. The Fick’s diffusive model was solved with effective moisture diffusivity of 5.24×10-10 m2 s-1 for 55°C and 7.01×10-10 m2 s-1 for 70°C. For experimentation, thin layers of pistachio nut, ‘Ohadi’ variety, were dried at high drying air temperatures (55 and 70°C), three replications for each treatment, along with drying air velocity and relative humidity of 0.5 m s-1 and 20%, respectively. Good agreement was observed when the output of model was compared with the experimental data. Mean Relative Deviation (MRD) calculated for the model and the experimental data for the air temperatures 55 and 70°C, were found to be 6.2% and 8.1%, respectively.