The ultrasound device (including ultrasound generator and output terminal), whose frequency was 20kHz and power was adjustable in the range of 0–600W, is shown in Fig. 7. The vibration of the ultrasound generator was amplified through the transducer to generate ultrasound, finally ultrasound was introduced into the medium through the booster. In this experiment, ultrasound was introduced into water in a glass container with size Φ 100mm×200mm, the booster was immersed in water 10mm deep, the power of ultrasound generator was 200W. The diameter of the booster was 30mm, the water level in the container was 180mm. A high-speed CCD snapping system was utilized to record the fluid flow. Numbers of observing points in the flow field were selected to calculate the displacements of bubbles by a series of recorded frames, as a result, the velocity betaxolol of each bubble were determined to reveal the appearance of streamline in the flow field. The flow field recorded by the high-speed CCD system is shown in Fig. 8, from which it can be seen that there was intense turbulence along the center-line below the booster’s tip.
As the flow field was symmetric, 34 typical points roughly uniformly distributed in the right side were selected as the observing points, as illustrated in Fig. 9(b). Each observing point has a start and an end location, the former location stands for the position where the observing point lies in the first frame of video recording, and the latter one was the location of the observing point in the last frame of video recording. The velocity vector of each observing point was obtained through the calculation based on its start and end positions and the time differences between two consecutive recorded frames, the results are listed in the table below. The streamline of the whole flow field is plot in Fig. 9(b).
The velocity distribution in water obtained by numerical simulation is illustrated in Fig. 2(a), from which it can be seen that velocity in the area where y<20mm is the highest, it is helpful to compare the experiment and simulation results in this area. The points along the depth direction (x direction) at the locations where y=0, 15mm and 20mm were selected for study, the velocity at these points was measured using high-speed CCD system, the comparison of velocity in experiment and simulation is shown in Fig. 10. The velocity in experiment is approximate to that in simulation, but the experiment results are slightly higher than the simulation results, as the ultrasonic energy released during experiment increased the water temperature, leading to the decrease of water’s viscosity. When the water temperature increased from 0°C to 40°C, the viscosity decreased from 1.7921×10−3Pas to 0.6560×10−3Pas , as a result, the velocity of water flow increased. However, the heating effect of ultrasonic treatment is ignored in simulation, the viscosity of water is considered to be a constant, in this way, the velocity in experiment is higher than that in simulation. The variation trends of velocity in experiment and simulation are similar, indicating that numerical simulation reveals the ultrasonic streaming correctly.
The comparison of the streamline obtained in experiment and simulation is illustrated in Fig. 9, it can be seen that the simulated streamline is in agreement with the experimental one.
This research was supported by National Natural Science Foundation of China (No. 51075299).
Despite the many and varied potential applications of high power ultrasound technologies for different treatment purposes, industrial scalability of ultrasonic treatment processes is still difficult to achieve. One of the crucial elements of ultrasound scalability is the quantification of energy losses involved in the conversion of the electrical energy into several forms of mechanical energy . The ultrasonic energy distribution of acoustic cavitation effects within an ultrasonic reactor is also important for scalability as this aspect allows engineers to determine the optimum operating conditions for a particular application. Furthermore, scrutinizing energy conversion in ultrasonic reactors enables researchers to rigorously compare results of different experiments and report reproducible reaction conditions .