Modeling of some pistachio drying characteristics in fix, semi fluid and fluid bed dryer

Abstract

Modeling of pistachio (cv. Ohadi) drying kinetic was carried out in a thin layer dryer of fix, semi fluid and fluid bed. Initial moisture content of pistachio samples was about 50.3% (d.b.).  Three drying characteristics of effective diffusivity, energy of activation and specific energy consumption were computed and influences of drying parameters were investigated.  Air temperature levels of 45, 60, 75 and 90℃ and bed conditions of fix, semi fluid and fluid bed were applied in these experiments.  Six mathematical models were used to predict the moisture ratio of pistachio samples in thin layer drying. Results showed that the Two-term model had supremacy in prediction of pistachio drying behavior.  Effective moisture diffusivity of pistachio was calculated using Fick’s second law.  Maximum and minimum values of effective moisture diffusivity calculated between 8.60×10^-9 m²/sand 1.98×10^-9 m²/s, respectively.  The calculated values of energy of activation for pistachio samples were computed between 30.52 kJ/mol and 35.26 kJ/mol for temperature boundary of 45 to 90℃ and bed conditions of fix to fluid bed.  Specific consumption of energy in thin layer drying of pistachio varied between 0.531×10⁶and 1.447×10⁶kJ/kg. Increase in air temperature in each bed condition cause decrease inspecific consumption of energy.  These pistachio properties are necessary to design the dryer system and to adjust the dryer in the best point.

Keywords: Two-term model, thin layer drying, pistachio, diffusivity, energy