Abstract
Abstract Different aspects of soybean drying such as energy and exergy analyses, quality, mass transfer parameters, and modeling of drying kinetics were investigated in a microwave dryer. Results showed that energy and exergy efficiency increased with increasing microwave power, while values of energy efficiency (33.70 to 66.0%) were higher than exergy efficiency (23.38 - 48.30%). Specific energy consumption and energy loss varied 4.93 to 9.11 MJ/kg water and 5.04 to 8.89 MJ/kg water, respectively. Approximately 8.94 to 20.07% of the total energy input is consumed by increasing of the product temperature. The values of improvement potential changed between 1.31- 5.35 MJ/kg water. Bulk density, degree of shrinkage and rehydration ratio varied from 726.6 to 762.8 kg/m3, 0.888 to 0.910, and 0.618 - 0.799, respectively. Parameters total color change (14.68 - 19. 89) and hue angle (88.07 to 91.73o) increased with increasing microwave power. Effective diffusivity and mass transfer coefficient varied from 1.99×10−9 to 12.25×10−9 m2/s and 2.71×10−6 to 19.98×10−6 m/s, respectively. The activation energy was found to be 4.98 W/g for a diffusion model and 5.33 W/g for a mass transfer model. Among the models, the Page model was found to best describe the drying behavior of soybean.
Highlights
Soybeans are harvested typically at moisture contents in the range 25-33% wet basis
Specific energy loss varied from 8.89 to 5.04 MJ/kg water, which indicated that 67.4 to 86.1% of the energy given to the system was not used in drying the soybean samples (Figure 2)
Energy consumption for soybean seeds under fluidized bed and microwavefluidized bed drying was studied by Darvishi et al (2014b) and Khoshtaghaza et al (2014), no mention was found about investigation of the energy consumption and drying efficiency for soybean seeds undergoing microwave treatment
Summary
Soybeans are harvested typically at moisture contents in the range 25-33% wet basis. For safe storage, it is necessary to have a moisture content of soybeans less than 10% wet basis according to the local climate conditions (Darvishi et al, 2014a). The drying kinetics of food is a complex phe-nomenon and requires simple representations to predict the drying behavior, and for optimizing the drying parameters. Knowledge of both the moisture diffusivities and mass transfer coefficients for the various systems is essential, as more complex mathematical models and correlations which can provide a more in-depth understanding of the drying operations require data on specific mass transfer parameters (McMinn et al, 2003). The moisture diffusion of a food material characterizes its intrinsic mass transport property of moisture, which includes molecular diffusion, liquid diffusion, vapour diffusion, surface diffusion, capillary flow, hydrodynamic flow and other
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