Jihyang Kim

Numerical analysis for the optimum condition of ultrasonic nebulizing

To obtain the optimal driving conditions for ultrasonic nebulizing, the capillary wave caused by ultrasound on the water surface was analyzed theoretically. From the possible solutions of Mathieus equation, the condition for amplitude diverging with time changes was investigated. The possible ranges of the driving frequency and the vibration displacement for nebulizing were obtained numerically, and the droplet size distribution was obtained in these ranges. The results of this study could be applied to design the desirable ultrasonic nebulizer.

Improvement of compaction rate of radioactive samples for gamma spectrometry using high power ultrasound

As interest of environmental radiation has increased, accurate analysis of the environmental radioactive sample has been demanded. The gamma ray spectroscopy is generally used to analyze the environmental radiation for solid radioactive samples such as soil compacted in a standard container. To improve the accuracy of the analysis, it is necessary to compact as much sample of the powder state as possible. Compacted amount of the sample and its density could be different depending on the force from measuring person in the case of conventional method using a compacting rod. In this study, we propose a method to improve the compacting rate with high power ultrasound for solid radioactive sample of powder state.

Size distribution of nanoparticles in the droplets ultrasonically atomized from Al2O3 suspension

In this study, a recollection method only for particles below a certain size involving ultrasonic atomization was suggested. Nanoparticles were separately recollected by using the suggested method with the suspension made of alumina powder of 300 nm center diameter and the particle distributions in the recollected suspension were observed using an optical microscope. Furthermore, the size distribution of the recollected particles depending on the surface tension of the suspension was investigated. Results indicate that the sizes of the particles in the recollected suspension were reduced by decreasing the surface tension of the suspension. In the suggested method, the maximum diameter of the recollected nanoparticles could be controlled by changing the surface tension of the suspension.

Ultrasonic streaming and cavitation for nano particle dispersion

Recently, non-contact type ultrasonic dispersion technique is attracting attention in various industrial fields. To disperse the nano particle suspension effectively, new dispersion system was suggested using arrayed piezoelectric vibrators with high resonant frequency. The suggested system has high intensity ultrasonic field and stirring effect caused by eddying current because the piezoelectric vibrators, which are arrayed on inner surface of a metal cylinder and tilled by the regular degree, generate focused ultrasound and make streaming effect on nano particle suspension. The system has the erosion dispersion caused by the ultrasonic shock wave due to the ultrasonic cavitation as well as the division dispersion caused by shear stress of the fluid from the eddy current due to the ultrasonic streaming in the suspension, simultaneously. To confirm these effects, TiO2 suspension was dispersed with the suggested system and the effectiveness of the systems was confirmed.

Separation of single nano particles from suspension by using ultrasonic atomization

It is very important to obtain non-agglomerated nano particle state for practical application of nano technology. In order to improve the functionality of products using nano particles, more precise control of particle size distribution is required in their synthesis process. However, synthesized nano particles are agglomerated due to physical and chemical reasons, and it veils the unique properties of nano particles and has disturbed their practical use. In this study, we propose a separation method for nano particles from suspension by using the droplets as the separation space. The particle size distribution of nano particles in the recollected suspension was measured. From the results, it was confirmed that it is possible to separate and to recollect monodispersed nano particles from original suspension with 0.002 wt.% TiO2 powder by using suggested method.

Sound speed change with concentration in nano particle suspension

Based on the multi-scattering theory for the micro particles, sound speed of the TiO2 nano particle suspension with ultra-low concentration was estimated. Good agreement was found between the estimated results and the experimental ones. The sound speed of 5 MHz ultrasound was measured with high accuracy, decreasing by about 0.15 m/s as concentration of suspension was changed in the range from 0.002 wt.% to 0.02 wt.%. From the experimental result, it is expected that the concentration of nano particle suspension is possibly estimated from the sound speed change.

Concentration of liquid sample for gamma-ray spectroscopy with ultrasonic nebulization

Radionuclide analysis of sea water is necessary to monitor environmental contamination due to the radioactive substances from nuclear facilities. However, it is difficult to analyze the nuclides promptly with the conventional method of coprecipitation during emergencies because the method requires long precipitation times. In this study, an effective concentration method with ultrasonic nebulization was suggested for sea water samples. When a sea water sample of 40 L was concentrated, 30 h was required with the conventional method, whereas it took less than 11 h with the suggested method. The validity of the suggested method was verified by gamma-ray spectroscopy.