• 대한기계학회논문집B
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• 제31권2호
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• pp.195-201
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• 2007

A visualization study of flow characteristics in a mixer using multi-nozzle bubbling was performed. The mixer is filed with liquid glycerin (dynamic viscosity = $1000mPa{\cdot}s\;at\;25^{\circ}C$) and convective mixing is induced by air bubbles generated from 9 orifices installed on the bottom of the mixer. To visualize the flow field, PIV (Particle Image Velocimetry) system consisting of 532nm Nd:YAG laser, $2k{\times}2k$ CCD camera and synchronizer is adopted. The bubbles generated with uniform size and frequency form bubble stream and bubble streams rise vertically without interaction between bubble streams. Mixing efficiency is affected by the height of bubbler and the effective height of bubbler is 20nm from the bottom of the mixer.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2006년도 추계학술대회 논문집
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• pp.48-54
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• 2006

A visualization study of flow characteristics in a mixer using multi-nozzle bubbling was performed. The mixer is filled with liquid glycerin (dynamic viscosity = $1000mPa{\cdot}$ s at $25^{\circ}C$) and convective mixing is induced by air bubbles generated from 9 orifices installed on the bottom of the mixer. To visualize the flow field, PIV (Particle Image Velocimetry) system consisting of 532nm Nd:YAG laser, $2k\times2k$ CCD camera and synchronizer is adopted. The bubbles generated with uniform size and frequency form bubble stream, and bubble streams rise vertically without interaction between bubble streams. Mixing efficiency is affected by the height of bubbler and the effective height of bubbler is 20mm from the bottom of the mixer.

• Environmental Engineering Research
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• 제24권3호
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• pp.382-388
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• 2019

Although nanobubbles attract significant attention, their characteristics and applications have not been thoroughly defined. There are diverse opinions about the definition of nanobubbles and controversy regarding methods that verify their characteristics. This study defines nanobubbles as having a size less than $1{\mu}m$. The generation of these sub-micron (nano) bubbles may be verified by induced coalescence or light scattering. The size of a sub-micron (nano) bubbles may be measured by optical, and confocal laser scanning microscopy. Also, the size may be estimated by the relationship of bubble size with the dissolved oxygen concentration. However, further research is required to accurately define the average bubble size. The zeta potential of sub-micron (nano) bubbles decreases as pH increases, and this trend is consistent for micron bubbles. When the bubble size is reduced to about 700-900 nm, they become stationary in water and lose buoyancy. This characteristic means that measuring the concentration of sub-micron (nano) bubbles by volume may be possible by irradiating them with ultrasonic waves, causing them to merge into micron bubbles. As mass transfer is a function of surface area and rising velocity, this strongly indicates that the application of sub-micron (nano) bubbles may significantly increase mass transfer rates in advanced oxidation and aeration processes.

• Journal of Welding and Joining
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• 제24권2호
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• pp.71-78
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• 2006

It has been reported that good quality weld beads are not easily obtained during the $CO_2$ CW laser welding of primer coated plate. However, by introducing a small gap clearance in the lap position, the zinc vapor can escape through it and sound weld beads can be acquired. Therefore, this study examines for keyhole behavior by observing the laser-induced plasma and investigates the relation between keyhole behavior and formation of weld defect. Laser-induced plasma has accompanied with the vaporizing pressure of zinc ejecting from keyhole to surface of primer coated plate. This dynamic behavior of plasma was very unstable and this instability was closely related to the unstable motion of keyhole during laser welding. As a result of observing the composition of porosity, much of Zn element was found from inner surface of porosity. But Zn was not found from the dimple structure fractured at the weld metal. By analyzing of vaporizing element in laser welding, a component ratio of Zn was decreased by introducing a small gap clearance. Therefore we can prove that the major cause of porosity is the vaporization of primer in lap position. Mechanism of porosity-formation is that the primer vaporized from the lap position accelerates dynamic behavior of the key hole and the bubble separated from the key hole is trapped in the solidification boundary and romaines as porosity.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.709-713
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• 2004

Characteristics of laser-assisted wet etching of titanium in phosphoric acid were investigated to examine the feasibility of this method for fabrication of high aspect ratio microchannels. Laser power, number of scans, etchant concentration, position of beam waist and scanning speed were taken into consideration as the major process parameters exerting the temperature distribution and the cross sectional profile of etched channels. Experimental results indicated that laser power influences on both etch width and depth while number of scans and scanning speed mainly affect on the etch depth. At a low etchant concentration, the cross sectional profile of an etched channel becomes a U-shape but it gradually turns into a V-shape as the concentration increases. On the other hand, surface of the laser beam focus with respect to the sample surface is found to be a key factor determining the bubble dynamics and thus the process stability. It is demonstrated that metallic microchannels with different cross sectional profiles can be fabricated by properly controlling the process parameters. Microchannels of aspect ratio up to 8 with the width and depth ranges of 8∼32 m and 50∼300 m, respectively, were fabricated.

• 대한소아치과학회지
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• 제25권4호
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• pp.761-771
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• 1998

In this study, attempt has been made to evaluate the effect of $CO_2$ laser irradiation on enamel surface structure and the bond strength of sealant material. Conventional acid etching was used as a control technic for comparison. The results obtained from this experiment were as follows; 1. The highest mean shear bond strength value was observed in samples of Group I (acid-etching) with the statistical significance(p<.05) between all the other groups. 2. The shear bond strength in Group IV was the lowest among laser etching groups. but there were no significant difference between them(p>.05). 3. Scanning electron microscopic observation showed that the rough and irregular surface was created by $CO_2$ laser treatment with the formation of numerous pores, micro-cracks, and small bubble-like inclusion. Increasing the energy density induced localized surface melt with a thin smooth glaze-like appearance. 4. In acid-etched control specimen cohesive failure predominated, whereas adhesive failure was the main mode in laser-treated group. Based upon the above-mentioned results, it can be assumed that the $CO_2$ laser is not an adequate substitute for the acid-etch technique in enamel preconditioning. More studies are required to explore the effective condition of laser irradiation which could attain the better bond strength of restorative materials.

• 전기전자학회논문지
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• 제28권1호
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• pp.97-103
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• 2024

일부 약물은 피부의 표피층 이하로 주입될 때 훨씬 더 효과적인 의료 효과를 제공할 수 있다. 그러나 전통적인 비침습 주입 장치는 피부의 한 부분에 상대적으로 많은 양의 약물을 전달하며, 이는 조직층 구조를 분리하여 멍과 출혈을 유발할 수 있다. 피부의 큰 표면적에 빠른 반복율로 소량을 주입함으로써 환자의 부상과 통증을 감소시킬 수 있다. 이를 위해서 약액을 분사하는 압력은 빠른 속도로 침투 가능 압력까지 상승되고 빠르게 하강하여 주입되지 않는 되튀김량을 줄이고, 주입량을 최소화해야한다. 이러한 형태의 비침습 주사 장치가 개발되었지만 그 장치들의 의학적 효능은 분석된 바가 거의 없다. 따라서 이 연구에서는 속도가 ~310m/s인 마이크로젯을 분사하는 레이저 유도 마이크로젯 장치를 개발했다. 펄스 시간은 400~800 ㎲이며 각 분사가 초당 10번 반복되는 속도로 약물을 약 1 µL 분사할 수 있습니다. 이러한 원리를 사용하여 우리는 마우스 모델에 대한 약물 주사의 효과를 평가했다. 마우스 모델에 인슐린 용액을 주입한 후 혈중 인슐린 농도를 측정하였으며, 일반 바늘 주사 주법과 동일한 값을 얻었다.