Determination of optimized condition of pistachio drying process in a microwave fluidized bed dryer

In this research the effect of different drying conditions of microwave fluidized bed (inlet air temperature, inlet air velocity and microwave power) on drying time, effective moisture diffusivity, shrinkage and total energy consumption of pistachio kernel was studied. Data analysis and optimization of drying process of pistachio were conducted by response surface method and central composite design. Input (independent) parameters were: inlet air temperature, inlet air velocity and microwave power. Dependent (output or response) variables were: drying time, effective moisture diffusivity, shrinkage and total energy consumption. The primary moisture content of pistachio kernels has been determined 0.569 (d.b.). Drying of the kernels was performed at three levels of air velocity (1.16, 3.32 and 8.48 m/s), three levels of input air temperature (40, 55 and 70°C) and three levels of microwave power (220, 330 and 440W). The obtained effective drying time, moisture diffusivity, shrinkage and total energy consumption of pistachio ranged between 1.2 to 3.83 h, 2.7×10-10 to 1.32×10-09 m2/s, 12.01% to 35.43% and 0.337 to 1.63 kWh, respectively. The optimum point occurred at air temperature of 38.48˚C, air velocity of 1.16 m/s and microwave power of 440 W. Response variable values for drying of Akbari cultivar of pistachio with fluidized bed microwave dryer at this point were drying time of 2.677 h, effective moisture diffusivity of 5.179×10-10, shrinkage percent of 18.41% and total energy consumption of 0.7109 kWh.