Pistachio Nut (Ohadi) Moisture Simulation During Drying with High Temperature Finite Element Method

Pistachio nut is an edible seed produced by the pistachio tree. Drying is an important operation in pistachio processing. The moisture content of pistachio nuts decreases from 37-40 % (w.b.) to 5-6 % during drying process. The high quality of pistachio nuts depends on fast and efficient handling and drying operation. Drying conditions (drying air temperature, air velocity, relative humidity and initial moisture content) of pistachio nut affect on quality, chemical and microbial attributes of dried nuts. Thus the drying process must be understood and controlled. This requires an accurate description of the drying mechanism. In this study the finite element formulation and solution of diffusive moisture transfer equations to improve grain drying simulation of axisymmetric bodies is presented. Model was solved with improvement moisture diffusivity (7.5E-10 m2/s for 70°C and 5E-10 m2/s for 55 °C). For experiment, thin layer pistachio nut, ‘ohadi’, was dried with two drying air temperature 55 and 70°C) and during drying air velocity and relative humidity were 1.5 m/s and 20%, respectively. During drying, moisture was measured every minute. Good agreement has been observed when the output of model was compared to experimental data. Relative deviance average that calculated of improvement model for air temperature 55 and 70°C with experimental data, respectively were 5.3% and 8.4%. This result shows that simulation model is near experimental data. Model is used for moisture simulation of pistachio nut drying. The simulated moisture profile and gradient are directly usable for stress cracking analyses of pistachio nut. The results of the finite element analysis can be used for pistachio nut quality evaluation and drying simulation studies.