• Journal of the Korean Ceramic Society
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• v.34 no.7
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• pp.747-757
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• 1997

ZSM-5 zeolite composite membranes have been synthesized from a silica sol solution containing TPABr as an organic template by the dip-coating and the pressurized-coating hydrothermal treatment techniques. The CO2 separation efficiency of synthesized composite membranes was also investigated. The permeation mechanism of CO2 through ZSM-5 membranses was the surface diffusion, and that of N2, O2, and He gases was Knudsen diffusion or activated diffusion depending on the synthetic method of membranes and the measurement temperature. The CO2/N2 separation factor of the membrane prepared by the dip-coating hydrothermal treatment was 2.5 at about 12$0^{\circ}C$, while the ZSM-5 composite membrane synthesized by the pressurized-coating hydrothermal treatment technique showed the CO2/N2 separation factor of 9.0 at room temperature higher than that ever reported in the literature.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.2
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• pp.45-50
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• 2008

Molecular flows inside a guide block in the OLED(organic luminescent emitting device) deposition process have been simulated using DSMC(direct simulation Monte Carlo) method. Because the organic materials are evaporated under vacuum, molecules flow at a high Knudsen number of the free molecular regime, where the continuum mechanics is not valid. A guide block is designed as a part of the linear cell source to transport the evaporated materials to a deposition chamber, When solving the flows, the inlet boundary condition is proved to affect significantly the whole flow pattern. Thus, it is proposed that the pressure should be specified at the inlet. From the analysis of the density distributions at the nozzle exit of the guide block, it is shown that the longer nozzle can emit molecules more straightly. Finally, a nondimensionalized mass flow profile is obtained by numerical experiments, where various nozzle widths and inlet pressures are tested.

• Proceedings of the Membrane Society of Korea Conference
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• 1992.10a
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• pp.5-6
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• 1992

무기막은 고분자 계통의 유기막과는 달리 200$\circ$C 이상의 고온에서도 높은 기체 투과도와 구조적 안정성을 보인다. 따라서 무기막을 고온의 촉매 반응에 이용하면 생성물 중 일부를 선택적으로 분리시키므로써 열역학적으로 예측할 수 있는 값 이상의 높은 전환율을 얻을 수 있으며, 또한 반응물 중 일부를 막을 통해 주입하면 반응의 정도를 조절함으로써 원하는 생성물의 수율을 높일 수 있게 된다. 그러나, 현재 실험실에서 많이 연구되고 있는 다공성 유리 또는 다공성 알루미나와 같은 무기막들은 기체 투과도는 높은 반면에 기체 분리가 Knudsen diffusion에 의해 이루어지기 때문에 분리선택도가 낮은 단점이 있다.

• Proceedings of the Membrane Society of Korea Conference
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• 2004.05a
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• pp.128-131
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• 2004

The composite mesoporous ceramic membranes were prepared with ${\gamma}$-alumina and poly (2, 6-dimethyl-l, 4-pyphenylene oxide) (PPO) on the surface of the macroporous $\alpha$-alumina ceramic membranes and the permeation results were compared with those of the $\alpha$-alumina membrane for large-scale applications. In the results of the transport experiments, the ceramic membranes gave high gas permeances mainly due to Knudsen diffusion and surface diffusion as an additional mechanism. And, the polymer modification increased the permeances of the strongly adsorbing gas components. In this study the modifications of alumina ceramic membranes could increase the gas permeation performances especially for the strongly absorbing gas components.

• Proceedings of the Membrane Society of Korea Conference
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• 2005.11a
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• pp.119-123
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• 2005

The thermochemical splitting of water has been proposed as a clean method for hydrogen production. The IS process is one of the thermochemical water splitting processes using iodine and sulfur as reaction agents. HI decomposition procedure to obtain hydrogen is one of the key operations in the process, because equilibrium conversion of HI is low (22% at $450^{\circ}C$). The silica membranes prepared by CVD. method were applied to the decomposition reaction of HI vapor. The permeation characteristics of hydrogen and nitrogen belong to the Knudsen flow pattern.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.105.2-105.2
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• 2013

배기속도 2500 L/s, 최고진공도 10-10 mbar의 구현을 목표로 하는 대용량 복합 분자펌프 설계를 위한 3차원 유동해석을 실시하였다. 진공도가 10-5 mbar 이상이 되는 고진공도에서는 Knudsen 수가 102 이상이 되어러 분자간 충돌을 거의 무시할 수 있게 되며, 이때의 유체해석 방법으로서는 통상 희박기체 해석법으로 많이 쓰이는 Direct simulation Monte Carlo 방법보다, 충돌이 없는 분자의 자유운동을 모사하는 Monte Carlo 방법이 더 적합할 수 있다. 본 연구에서는 다단계 rotor와 stator로 구성되는 복합분자 내 유동장에 Monte Carlo 해석법을 적용하여 유동해석을 실시하였다. 다양한 변수의 조합에 대한 수치적 해석에서, 복합분자펌프의 성능에 영향을 미치는 중요한 설계변수는 rotor-stator의 날개각, 유동방향 회전축의 두께 변화 등, 진행방향 분자의 모멘텀에 직접적인 영향을 미치는 변수들임이 확인되었다.

• Laser Solutions
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• v.6 no.3
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• pp.37-45
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• 2003

Pulsed laser ablation is important in a variety of engineering applications involving precise removal of materials in laser micromachining and laser treatment of bio-materials. Particularly, detailed numerical simulation of complex laser ablation phenomena in air, taking the interaction between ablation plume and air into account, is required for many practical applications. In this paper, high-power pulsed laser ablation under atmospheric pressure is studied with emphasis on the vaporization model, especially recondensation ratio over the Knudsen layer. Furthermore, parametric studies are carried out to analyze the effect of laser fluence and background pressure on surface ablation and the dynamics of ablation plume. In the numerical calculation, the temperature, pressure, density, and vaporization flux on a solid substrate are obtained by a heat-transfer computation code based on the enthalpy method. The plume dynamics is calculated considering the effect of mass diffusion into the ambient air and plasma shielding. To verify the computation results, experiments for measuring the propagation of a laser induced shock wave are conducted as well.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.22-22
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• 2010

배기속도 2500 L/s, 최고진공도 $10^{-10}$ mbar를 구현할 대용량 복합 분자펌프 설계를 위한 3차원 유동해석을 실시하였다. 진공도가 $10^{-5}$ mbar 이상이 되는 고진공도에서는 Knudsen 수가 $10^2{\sim}10^7$에 이르러 분자간 충돌을 거의 무시할 수 있게 되며, 이때의 유체해석 방법으로서는 통상 희박기체 해석법으로 많이 쓰이는 Direct simulation Monte Carlo 방법보다, 충돌이 없는 분자의 자유운동을 모사하는 Monte Carlo 방법이 더 적합하게 된다. 본 연구에서는 다단계 rotor와 stator로 구성되는 복합분자 내 유동장에 Monte Carlo 해석법을 적용하여 유동해석을 실시하였다. 먼저 2차원 해석을 실시하여 분자펌프의 성능에 중요한 영향을 미치는 설계변수들을 도출하고, 이 설계변수들의 최적값을 다양한 3차원 유동해석을 통해 도출하였다. 해석결과는 펌프설계에 적용되어 펌프 성능시험결과를 통해 확증된다.

• Korean Journal of Remote Sensing
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• v.17 no.4
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• pp.297-305
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• 2001

Ocean satellite altimetry-implied free-air gravity anomalies have had the shortest wavelengths removed during the processing to generate the optimal solution between multiple radar altimeter missions. ERS-1 168day mission altimetry was residualized to a reference geoid surface generated by integrating Anderson & Knudsen’s free-air gravity anomalies for the Barents Sea. The altimetry tracks were reduced and filtered to extract the shortest wavelengths (between 4 and 111 km) from both ascending and descending tracks, respectively. These data were recombined using existing quadrant-swapping techniques in the wavenumber domain to generate a correlated, high frequency gravity field related to the local geologic sources. This added-value surface adjusted the reference free-air gravity anomalies to better reflect features in the gravity field at a wavelength related to the distance between altimetry ground tracks.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.309-317
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• 2012

Recent years have witnessed the use of micro shock tube in various engineering applications like micro combustion, micro propulsion, particle delivery systems etc. The flow characteristics occurring in the micro shock tube shows a considerable deviation from that of well established conventional macro shock tube due to very low Reynolds number and high Knudsen number effects. Also the diaphragm rupture process, which is considered to be instantaneous process in many of the conventional shock tubes, will be crucial for micro shock tubes in determining the near diaphragm flow field and shock formation. In the present study, an axi-symmetric CFD method has been applied to simulate the micro shock tube, with Maxwell's slip velocity and temperature jump boundary conditions. The effects of finite diaphragm rupture process on the flow field and the shock formation was investigated, in detail. The results show that the shock strength attenuates rapidly as it propagates through micro shock tubes.