• Journal of Korean Vacuum Science & Technology
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• 제2권2호
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• pp.133-138
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• 1998

To enhance the ionization level of I-PVD and reduce the coil voltage two approaches were tried and as a diagnostic, optical emission spectroscopy and impedance analysis of the plasma was done with a range of Ar pressures and RF power along with XRD analysis of deposited Ag films. RF sputtering power was pulsed with various on/off time scales to recover the ICP quenched by sputtered metals. This in average enhances the ionization of the sputtered atoms with 10 ms/10 ms and 100 ms/100ms pulse on/off time duration and gives higher (200) preferred orientation over (111) in deposited Ag films. Secondly, Small axial B field about 8G remarkably reduced RF coil sputtering and showed scaled relationship between RF power and magnetic field strength for optimal process condition. From OES of Ar0 and Ar+, wave-like dispersion structure appeared and reduced the coil voltage about 20% at very weak field strength of 8G. This should be studied further to have nay relation with low mode helicon wave launching.

• 대한기계학회논문집B
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• 제23권10호
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• pp.1327-1339
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• 1999

Characteristics of two-phase flow and heat transfer were numerically investigated in a submerged gas Injection system. Effects of both the gas flow rate and bubble size were investigated. In addition, heat transfer characteristic and effects of heat transfer were investigated when temperature of the injected gas was different from that of the liquid. The Eulerian approach was used for the formulation of both the continuous and the dispersed phases. The turbulence in the liquid phase was modeled by the use of the standard $k-{\varepsilon}$ turbulence model. The interphase friction and heat transfer coefficient were calculated by means of correlations available in the literature. The turbulent dispersion of the phases was modeled by introducing a "dispersion Prandtl number". The plume region and the axial velocities are increased with increases in the gas flow rate and with decreases in the bubble diameter. The turbulent flow field grows stronger with the increases in the gas flow rate and with the decreases in the bubble diameter. In case that the heat transfer between the liquid and the gas is considered, the axial and the radial velocities are decreased in comparison with the case that there is no temperature difference between the liquid and the gas when the temperature of the injected gas is higher than the mean liquid temperature. The results in the present research are of interest in the design and the operation of a wide variety of material and chemical processes.

• KSBB Journal
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• 제7권1호
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• pp.59-65
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• 1992

외부 순환식 공기리프트 반응기에서 기상유속과 액상의 점도를 변수로 하여 기체체류량과 액체의 순환시간, 혼합시간, 순환속도 및 축방향분산계수를 측정하여 다음과 같은 결론을 얻었다. 1. 기체체류량은 기체유속이 증가함에 따라 증가 하였으며, 점도가 증가함에 따라서는 약간 감소하는 경향을 보였다. 또 기체유속이 증가함에 따라 상승관에서는 기체체류량의 증가율이 감소한 반면 하강관에서는 증가하였다. 2. 기체유속이 증가함에 따라 순환시간 및 혼합시간은 초기에 급격히 짧아지다가 거의 일정한 값을 나타내었으며, 액체의 점도가 증가함에 따라 순환기산과 혼합시간은 모두 증가하였다. 3. 순환 액체의 속도는 기체의 속도에 따라 초기에 급격히 증가하나 기체속도가 약 5cm/sec이상이 되면 그 증가율이 매우 둔화되었으며, 점도가 증가함에 따라 약간 감소함을 알 수 있었다. 또한 압력수지식으로 예측한 이론값과 실험값은 낮은 기체유속 영역에서는 잘 일치하였으나 기체유속이 증가함에 따라 실험값이 이론값보다 작은 값을 나타내었다. 4. 기체유속이 증가함에 따라 Bodenstein number는 감소하였고, 축방향분산계수는 증가하였으며, 점도가 증가함에 따라 약간 감소하는 경향을 보였다. 본 실험범위에서 분산이 많이 일어나mixed folw에 근접함을 알 수 있었다.

• 한국진공학회지
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• 제9권3호
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• pp.285-289
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• 2000

축방향의 약한 자기장(약 1∼20 gauss)으로 자화된 inductively coupled plasm의 투과깊이와 전파 상수의 특성변화를 계산하였다. 자화 플라즈마에 있어서 전자밀도의 증가로 인한 플라즈마의 투과깊이 감소와, 그와 상반되는 충돌주파수 증가로 인한 투과깊이 증가를 고려하여, 보다 균일한 플라즈마 공정을 위한 기초 자료로서 중성 입자와 전자간의 충돌주파수, 전자밀도 및 자기장의 크기와 플라즈마 투과깊이 간의 상관관계를 확인하였다. 통상적인 저압 공정 플라즈마 조건하에서, 약 4.8 gauss의 자기장이 축방향으로 인가되는 경우 cyclotron 공명에 의해 투과깊이가 최소값을 가지는 것을 재확인하였으며, 그 이상의 자기장에서는 원형 편광파의 침투깊이를 비롯한 제반 특성의 급격한 변화를 볼 수 있었다.

• Advances in nano research
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• 제7권6호
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• pp.379-390
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• 2019

Putting emphasis on the effect of existence of porosity in the functionally graded materials (FGMs) on the dynamic responses of waves scattered in FG nanobeams resulted in implementation of a novel porosity-based homogenization method for FGMs and show its applicability in a wave propagation problem in the presence of axial pre-load for the first time. In the employed porosity-dependent method, the coupling between density and Young's moduli is included to consider for the effective moduli of the FG nanobeam by the means of a more reliable homogenization technique. The beam-type element will be modeled via the classical theory of beams, namely Euler-Bernoulli beam theory. Also, the dynamic form of the principle of virtual work will be extended for such nanobeams to derive the motion equations. Applying the nonlocal constitutive equations of Eringen on the obtained motion equations will be resulted in derivation of the nanobeam's governing equations. Depicted results reveal that the dispersion responses of FG nanobeams will be decreased as the porosity volume fraction is increased which must be noticed by the designers of advanced nanosize devices who are interested in employment of wave dispersion approach in continuous systems for specific goals.

• 한국광학회지
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• 제6권4호
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• pp.324-330
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• 1995

단일모드광섬유에서의 유도브릴루앙산란을 설명하고 광원에 의한 기준신호 및 광섬유에서의 유도브릴루앙산란 신호를 이용해 헤테로다인 방식으로 주파수변화를 조사하였다. 수개의 종모드를 갖는 광원과 고리형 광섬유공진기를 결합하여 간단하게 스팩트럼분석기로 광섬유에서의 브릴루앙산란을 관측할 수 있다. 이 방법은 기준맥놀이 신호를 사용하기 때문에 13GHz 영역에서의 주파수변화를 수 GHz의 낮은 영역에서의 주파수변화로 브릴루앙산란 신호를 볼 수 있다. 분산천이광섬유와 크래딩에 Ti 도핑된 광섬유및 일반단일모드광섬유를 적절히 선택하여 13GHz 영역에서의 주파수변화를 수 GHz 이하의 영역에서 주파수변화로 조사하니 각각 3.32GHz, 900MHz 및 870MHz였다.

• 한국입자에어로졸학회지
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• 제9권4호
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• pp.231-238
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• 2013

Carbon nanotubes (CNTs) are one of the nanomaterials that were discovered by Iijima in 1991 for the first time. CNTs have long cylindrical and axi-symmetric structures. CNTs are made by rolling graphene sheets. Because of their large length-to-diameter ratio, they are called nanotubes. CNTs are categorized as single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) based on the shell structures. CNTs are broadly used in various fields, such as scanning probe microscopy, ultra fine nano balance and medicine, due to their extraordinary thermal conductivity, electrical and mechanical properties. Because long, straight CNTs have the same shape as asbestos, which cause cancer in cells lining the lung, there have been many studies on the effects of MWCNTs on human health that have been conducted. Stable atomization of CNTs is very important for the estimation of inhalation toxicity. In the present study, electro-static assisted axial atomizer (EAAA), which is the instrument that uses MWCNTs and aerosolizes them by transforming the single fiber shape using ultrasonic dispersion and electric field, was invented. EAAA consists of a ultrasonic bath for dispersion of MWCNTs and a particle generator for atomizing single fibers. The performance evaluation was conducted in order to assess the possibilities of 6-hour straight atomization with stability, which is the suggested exposure time in a day for the estimation of inhalation toxicity.

• 공업화학
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• 제8권3호
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• pp.416-424
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• 1997

본 연구에서는 고밀집 섬유체에 의한 정적 액-액 접촉기에 대한 이론적 모델링을 통하여 섬유체 접촉기 내부에서의 물질 이동과정과 각 상에서의 축 방향 농도분포 해석이 수행되었고, 여러 운전 조건하에서 출구 농도를 예측하여 실험치와 비교하였다. 본 섬유체 액-액 추출기는 그 구조적 특성 때문에 축 방향 분산이 없는 플러그 흐름 모델로 완벽하게 묘사될 수 있었으며 data fitting을 통해 결정되어 모델식에 적용된 물질전달 계수와 섬유체 추출기 축 방향 반위 길이 당 물질전달 면적의 곱의 항인 $k_a{\sigma}$은 그 섬유체 추출기의 고유 특성 값으로 사용될 수 있었고, 그 값은 약 0.0327cm2/sec이었다.

• 한국안전학회지
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• 제12권3호
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• pp.97-105
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• 1997

Mo-99(Molybdenum) is the only source of Tc-99m(Technetium) which is most frequently used in nuclear medical diagnostics and the demand is on the increase recently. Separation and refining of Mo-99 was investigated by adsorption and desorption on alumina. At pH=0.63, adsorption isotherm of Mo was fitted by Redlich ＆ Peterson equation using the adsorption experimental data. It was found that the pore diffusion model ($D_p=1.4{\times}10^{-6}cm^2/s, K_f/=0.4 cm/s$) agreed well with batch adsorption experimental data. RTDs(Residence Time Distributions ) were measured and axial dispersion coefficients were obtained in the fixed bed absorber according to the changes of the flow rate using 0.05% -NaCl. From the adsorption experimental data, it was shown that the behavior of breakthroughs depended on flow rate. Mo recovery yield was increased as adsorption flow rate was increased and desorption flow rate was decreased.

• Elastomers and Composites
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• 제24권2호
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• pp.105-109
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• 1989

ACF을 이용한 컬럼흡착에서 유기물의 액상흡착을 크로마토그래피에 의하여 측정하였다. 박테리아가 없는 상태에서의 텍스트로스의 흡착평형상수 Ka는 $72.5cm^3/g$이었으며 박테리아 공존상에서의 Ka값은 $87.9cm^3/g$을 나타내였다. 이것은 ACF상(床)의 박테리아의 존재가 유기물의 흡착평형상수 증가에 기여함을 알 수 있었다. 축방향혼합확산계수 Ez는 박테리아의 유무에 의존하지 않았다.