The effect of acoustic and solar energy on drying process of pistachios

Highlights: ► In this research, accelerated drying of pistachios under open sun by applying power ultrasound was investigated. ► No constant falling rate period of drying was observed. ► By applying the 20 kHz ultrasound about 17 W/kg, the drying period could be reduced to 4 h. - Abstract: A new approach of ultrasound-assisted sun drying was tested in this study using a flat bed as product support and two extensional piezoelectric Bolt-clamped 20 kHz transducer elements. The mono layer of moist unshelled pistachios was dried under open sun by applying 500 and 1000 W power ultrasound. The results showed that the Page model was found to be the most suitable for describing drying curve of pistachios. But, the Logarithmic model was described to satisfactorily drying curve of pistachios for open sun method when the ultrasound power was turned off. By applying the ultrasound about 17 W/kg moist pistachios in thin layer, the drying period could be reduced to 4 h