Rough rice convective drying enhancement by intervention of airborne ultrasound - A response surface strategy for experimental design and optimization

This study has examined the influence of ultrasonic-assisted hot air drying process on the dehydration behavior of in-bin rough rice (Oryza sativa) kernels. To this aim, the experimental drying kinetics of rough rice subjecting to different drying air temperatures (35, 40, 45, 50, and 55 degrees C) and inlet air velocities (0.2, 0.5, 0.8, 1.1, and 1.4 m/s) were carried out by applying various ultrasound power levels (30, 60, 90, 120, and 150 W) in the frequency of 21 kHz. The effect of ultrasound intervention was investigated on drying kinetics, effective moisture diffusivity, energy consumption, and product quality. Experimental plans were designed by response surface method to study the feasible interactions between research parameters. Based on the key results, high-power ultrasound in conjunction with conventional deep bed drying led in 26.47% decrease in drying time, 30.66% increase in moisture diffusivity, as well as improvement in the grain quality, in terms of acceptable reduction in head rice yield and whiteness losses. In addition, energy consumption reduced approximately by 24.36% when high-power ultrasound was applied at selected drying condition. Ultrasound intervention during hot air drying process is recommended as it generates rice kernels with desirable milling quality within shorter drying time.