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Abstract
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Current research studies the possibility of moderating convective drying of a packed bed of rough rice with ultrasound assistance at 21 kHz frequency. In this regard, a convective dryer equipped with an ultrasound generator was utilized to operate at an air temperature of 35–55 ◦C, velocity of 0.2–1.4 m s−1, and ultrasound power of 30−150 W for a bed thickness of 20 cm. For mathematical modeling of drying kinetics, the basic equations of mass and enthalpy conservation were implemented over an arbitrary control volume and solved by the finite difference method. The degradation kinetics of vitamin B3 concentration of the packed bed was also modeled using an empirical first-order kinetics model. Modeling results of the drying kinetics with (R2 of 0.9569−0.9889, RMSE of 0.014−0.073, and RCV of 3.341–6.378%) and without (R2 of 0.9402−0.9980, RMSE of 0.006−0.083, and RCV of 1.084–7.740%) sonication were coherent with the observed drying kinetics. The developed kinetic model for bioactiv- ity could also estimate the time evolution of vitamin B3 concentration of the dried product, acceptably. The key results revealed the noticeable effect of sonication on maintaining vita- min B3 concentration. The loss pattern of the forecasted vitamin B3 concentration within the bed was linear and diminished by the external action of ultrasound vibration during drying in lower air temperatures and high power levels.
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