Development and performance evaluation of ultrasound assisted microwave paddy dryer

• Ultrasound integrated continuous flow microwave grain dryer was designed & developed. • Performance of the developed dryer as thermal & quality of dried grain was evaluated. • Ultrasound treatment improves thermal efficiency and quality of dried grain. • Milling quality improved by drying treatment than control drying. • Higher microwave power caused fissure formation in grain. Energy efficient dryer, maintaining quality of dehydrated product, is an important aspect for all paddy processing countries. This study was sought to develop a small-scale ultrasound assisted continuous flow microwave dryer. Performance of the developed dryer was evaluated through energy analysis and quality attributes of the dried paddy. Ultrasound treatment applied for 5, 10 and 15 min and drying experiments were conducted at five microwave power (500, 1000, 1500, 2000 and 2500 W). Head rice yield, nutritional quality (lipid, protein, ash fiber, mineral) and color attributes were evaluated for the dehydrated paddy. Microstructure was evaluated to assess surface characteristics of paddy. Energy efficiency, thermal efficiency, drying efficiency and specific energy consumption of the developed dryer ranged between 25.5 and 60.1 %, 27.5 and 58.4 %, 20.8 and 33.4 % and 15.3 and 48.3 MJ/kg, respectively. Efficiency parameters become lower at higher microwave level while lower specific energy consumption was noted at lower microwave level. Energy performance was higher for the paddy pretreated by ultrasound. Nutritional value and lightness of the dehydrated paddy reduced and crack formation occurred while drying experiment conducted at higher microwave power.