Deep bed rough rice air-drying assisted with airborne ultrasound set at 21 kHz frequency: A physicochemical investigation and optimization

This study investigates the feasibility of achieving a modified rough rice air-drying with ultrasound intervention (US) set at 21 kHz frequency. The process was carried out using an ultrasound assisted convective dryer and analyzed in terms of drying time, energy consumption (EC), evaporation rate (ER), broken kernel (BK), water activity (a_w), vitamin B₃ (niacin), and total phenolic content (TPC). The lab-scale dryer was set to transmit energy at power levels of 30, 60, 90, 120, and 150 W in the air temperatures of 35, 40, 45, 50, and 55 °C and velocities of 0.2, 0.5, 0.8, 1.1, and 1.4 m/s for a thickness of 20 cm. The results showed that in-range drying parameters played a major role in response analysis, suggesting that ultrasound efficiency during convective drying heavily depends on the power, air temperature, and velocity levels. Ultrasound assistance significantly increased bed evaporation rate up to 38.93%. Subsequently, it caused a reasonable reduction in total drying time, EC, and BK percentage up to 27.92%, 25.98%, and 34.22%, respectively in the case of 35 °C, v = 0.8 m/s, and P = 90 W. Remarkable advances were attained in the ultrasound assisted drying domain in grain quality via acceptable decrease in niacin and TPC losses within shorter drying time. There was a significant linear trend in BK, niacin, and TPC values across the bed thickness, which all was increased by the ultrasound application. The highest nutrient retention and physical quality preservation belonged to the top layer, which was influenced by the ultrasound radiation by the highest degree.

The effect of high power airborne ultrasound and microwaves on convective drying effectiveness and quality of green pepper

The effectiveness of hybrid drying based on convective drying with application of ultrasound and microwave enhancement is the main subject of the studies. The drying kinetics, energy consumption as well as the quality aspect of green pepper is analysed. It was shown that hybrid drying methods shorten significantly the drying time, reduce the energy consumption and affect positively the quality factors. Each of the analysed aspects depend on combination of the convective-ultrasound-microwave drying programs. Besides, based on the drying model elaborated earlier by one of the authors, the effects of ultrasound on convective drying assessed by such phenomena as "heating effect", "vibration effect" and "synergistic effect" are presented.

Hybrid Drying of Carrot Preliminary Processed with Ultrasonically Assisted Osmotic Dehydration

In this paper the kinetics of osmotic dehydration of carrot and the influence of this pretreatment on the post-drying processes and the quality of obtained products are analysed. Osmotic dehydration was carried out in the aqueous fructose solution in two different ways: with and without ultrasound assistance. In the first part of the research, the kinetics of osmotic dehydration was analysed on the basis of osmotic dewatering rate, water loss and solid gain. Next, the effective time of dehydration was determined and in the second part of research samples were initially dehydrated for 30 min and dried. Five different procedures of drying were established on the grounds of convective method enhanced with microwave and infrared radiation. The influence of osmotic dehydration on the drying kinetics and final product quality was analysed. It was found that it did not influence the drying kinetics significantly but positively affected the final product quality. Negligible influence on the drying kinetics was attributed to solid uptake, which may block the pores, hindering heat and mass transfer. It was also concluded that the application of microwave and/or infrared radiation during convective drying significantly influenced the kinetics of the final stage of drying. A proper combination of aforementioned techniques of hybrid drying allows reducing the drying time. Differences between the particular dehydration methods and drying schedules were discussed.

Ultrasonic waves in diluted and densified suspensions

A theory of propagation of stress waves in diluted and densified suspensions is developed to make the theoretical basis for analysis of ultrasonic waves through these media. The formulae for the phase velocity and the attenuation coefficient are determined as the function of wave frequency and the suspension structure parameter, which is the volume or mass fraction of the solid phase. These formulae can be use, after suitable calibration, for determination of the solid volume fraction in diluted suspensions, and the solid mass fraction or the water content in densified suspensions, that is, parameters that characterize the structure of a suspension. These structure parameters can be determined by measuring the transition time of ultrasonic wave through a given distance of suspension. The phase velocity dispersion curves and the attenuation coefficients determined theoretically and experimentally are plotted as a function of the volume fraction of the solid phase for dilute suspension, or the solid mass fraction for densified suspension.