Modeling Infrared-Covective Drying of Pistachio Nuts under Fixed and Fluidized Bed Conditions

Abstract

The effect of bed condition (fix, semi fluid and fluid bed), input temperature (40, 55 and 70C) and infrared power (500, 1,000 and 1,500 W) on moisture diffusivity (Deff), activation energy (Ea) and specific consumption of energy (SCE) of pistachio nuts was investigated. The infrared radiation effect in fixed bed drying was further related to the other bed conditions. The maximum value of Deff (1.75 × 10−9) has been calculated at fix bed, air temperature of 70C and infrared power of 1,500 W. Infrared power, only in fix bed condition caused increase in Deff of pistachio nuts. Minimum and maximum of Ea for pistachio nuts under infrared condition varied from 25.95 to 56.07 kJ/mol. The maximum value of SCE (8.21 × 106 kJ/kg) was obtained at fluid bed (air velocity of 3.35 m/s), input temperature of 70C and infrared power of 1,500 W. Effect of infrared power in compare with the other input parameters was insignificant. Practical Applications Combining infrared with fluidization technique can be a novel method in drying of pistachio nuts. Infrared radiation with hot air fluidization provides an effective way to increase the drying rate and to prevent the nonuniform heat and mass transfer compare to the conventional drying methods. In order to design and evaluate of such new infrared process for pistachio, mathematical modeling of drying behavior in these infrared-convective heating systems is necessary. The modeling includes drying rate, effective Deff, Ea and SCE which are affected by a combination of thermal and physical properties as well as temperature, air velocity and infrared power. Developed models can be used to estimate more accurately the drying properties of pistachio nuts using computer and also can be used to optimize the drying process.