Effect of Ultrasound on Drying Kinetics of Rough Rice at Tempering Duration in an Infrared- Hot Air Combined Dryer

Rough rice is one of the most important agricultural products and it plays an important role in ensuring food security. The objective of this study was to investigate the effect of high power ultrasound in tempering duration on the drying kinetics of rough rice in a combined far-infrared radiation (FIR) dryer. Tests were conducted in a factorial design at four levels of ultrasound power density (Zero, 0.5, 0.75 and 1 kW/kg), four levels of frequency (20, 25, 28, and 30kHz) and three levels of drying air temperature (30, 40, and 50oC). Results showed that mechanical characteristics of rough rice were affected significantly at all ultrasound power and frequency levels at different inlet air temperatures at tempering duration and led to reduction of both drying time and specific energy consumption. So that at power of 0.5 kW / kg, low ultrasonic frequencies of 20 and 25 kHz and input temperature of 30 ° C while reducing the percentage of cracks in rough rice kernels, they also increase the energy required for healthy seed breakage on average.