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열천이 현상을 이용한 마이크로 펌프내의 희박기체유동 해석
허중식(Joong-Sik Heo),이종철(Jong-Chul Lee),황영규(Young-Kyu Hwang),김윤제(Youn J. Kim) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
Rarefied gas flows through two-dimensional micro channels are studied numerically for the performance optimization of a nanomembrane-based Knudsen compressor. The effects of the wall temperature distributions on the thermal transpiration flow patterns are examined. The flow has a pumping effect, and the mass flow rates through the channel are calculated. The results show that a steady one-way flow is induced for a wide range of the Knudsen number. The DSMC(direct simulation Monte Carlo) method with VHS(variable hard sphere) model and NTC(no time counter) techniques has been applied in this work to obtain numerical solutions.
허중식(Joong-Sik Heo) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.5
A simple analytical model of rarefied channel flow is developed to predict the compression ratio in a helical drag pump. If the surface velocity is zero, the model reduces to a capillary leaks. Predictions of our model agree well with the Knudsen's data for capillary leaks in transition flow, in addition to giving a good account of the Knudsen minimum. Also, the present results are compared with experimental data, and good agreement is obtained over the entire pressure range from molecular to slip flow.
허중식(Joong-Sik Heo),황영규(Young-Kyu Hwang),박종윤(Chong-Yun Park) 한국진공학회(ASCT) 1999 Applied Science and Convergence Technology Vol.8 No.2
하이브리드형 분자펌프를 구성하고 있는 원판형의 드래그펌프에 대하여 DSMC 수치해석을 이용한 성능해석을 수행하였다. 원판형위에 형성되어 있는 유로상의 기체유동은 3차원의 분자천이영역에 놓이게 된다. 상대적회전좌표계를 택하였기 때문에 분자 각각은 직선적이 아닌 곡선운동을 하게 된다. 따라서 본 연구에서는 코리올리스힘과 원심력을 포함한 미분방정식을 적분함으로써 분자 개개의 곡선궤적을 구하였다. 수 치해석시 분자충돌과정은 null-collision기법과 VSS(variable soft sphere)모델을 이용하여 계산하였으며, 이전의 선행연구와 비교한 결과 큰 차이를 보여주었다. 이것은 출구로 부터의 분자들의 역류에 의해 펌핑유로가 매우 제한되어지기 때문이며, 이러한 현상은 기존연구에서는 나타나지 않았다. Pumping performance of a disk-type molecular drag pump for a hybrid molecular pump is numerically analyzed by the direct simulation Monte-Carlo method. The flows in pumping channels are three-dimensional (3D) in a molecular transition regime. The main difficulty in modeling a 3D case comes from the rotating frame of reference. Thus, trajectories of particles are no longer straight lines. In the present study, trajectories of particles are calculated by integrating a system of differential equations including the Coriolis and centrifugal forces. The null-collision technique with a variable soft sphere molecular model is used for calculation of molecular collisions. The present numerical results significantly disagree with the previously known ones. This indicates that an actual pumping passage is very limited to a narrow region due to the significant backstreaming of molecules from the outlet.
황영규,허중식,최욱진,Hwang, Young-Kyu,Heo, Joong-Sik,Choi, Wook-Jin 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.6
Numerical and experimental investigations are performed for the molecular transition and slip flows in pumping channels of a disk-type drag pump. The flow occurring in the pumping channel develops from the molecular transition to the slip flow traveling downstream. Two different numerical methods are used in this analysis: the first one is a continuum approach in solving the Navier-Stokes equations with slip boundary conditions, and the second one is a stochastic approach through the use of the direct simulation Monte Carlo method. In the experimental study, the inlet pressures are measured for various outlet pressures in the range of 0.1{\sim}4Torr. From the present study, the numerical results of predicting the performance, obtained by both methods, agree well with the experimental data for the range of Knudsen number $Kn{\leq}0.1$ (i.e., the slip flow regime). But the results from the second method only agree with the experimental data for Kn>0.1(i.e., the molecular transition regime)
초저온용 밸브의 초저온성능 시험평가방법 국제표준에 대한 연구
김윤철(Yoon-Chul Kim),허중식(Joong-Sik Heo),황선역(Sun-Yeok Hwang) 표준인증안전학회 2013 표준인증안전학회지 Vol.3 No.2
There have not been international standards about the test evaluation for cryogenic valves so far. It just follows local or organization standards at the moment. To develop the international standard of cryogenic test method and procedure, we have studied domestic and international techniques and trends about the test method. We also have attended international conference meetings and seminars for technical agreement of the standard procedure and test method. The standard procedure has been revised by analysing a lot of test results using the standard test method. Finally we try to register the test method for cryogenic valves as an international standard through activities in the international working group or international conference meetings. In this paper, the results of the ISO international conference meeting(ISO/TC 153) at Canada are briefly presented.
3단 원판형 드래그펌프의 배기 성능에 관한 실험적 연구
황영규(Young-Kyu Hwang),허중식(Joong-Sik Heo),권명근(Myoung-Keun Kwon),양성민(Seong-Min Yang) 한국유체기계학회 2001 유체기계 연구개발 발표회 논문집 Vol.- No.-
In this paper, the pumping performance of the three-stage disk-type drag pump which works in the outlet pressure range from 4 to 0.01 Torr is studied experimentally. The rotational speed of the pump is 24,000rpm, and nitrogen is used as a test gas. The pumping characteristics of various drag pumps are investigated. The inlet pressures are measured for various outlet pressures of the test pump. The maximum compression ratios for zero throughput are measured for three-stage, two-stage BSC type, helical-type, one-stage BSC type and one-stage OSC type, respectively.
플라즈마 전극에서의 금속증기 발생이 SF₆ 아크 특성에 미치는 영향
이종철(Jong Chul Lee),허중식(Joong Sik Heo),이진형(Jin Hyung Lee),김윤제(Youn Jea Kim) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
The present work is a computational investigation of thermal plasmas in SF? switchgear, which burns in a mixture of working gas and PTFE and metal vapors resulting from nozzle ablation and electrode erosion, respectively. In order to solve the concentration of PTFE and electrode vapors conservation equations for the PTFE vapor and the metal vapor are solved together with the governing equations for mass, momentum, and energy of the gas mixture under the assumptions of local thermodynamic equilibrium (LTE) and local chemical equilibrium (LCE). The influence of metal vapor due to electrode evaporation on the arc behavior in SF? switchgear can be explained with some important parameters indicating the characteristics of SF? arc plasma. First, temperature in arc column is considerably different from that of the case without contact evaporation. The contamination by metal vapors cause the arc radius to be broadened and the core temperature to be lower than that of the case not considered the evaporation. Second, the concentration of PTFE vapor from nozzle surfaces can more easily move to the expansion chamber during high current period due to the existence of metal vapors near electrodes. Finally, the electrical conductivity in the arcing zone can be higher and may negatively affect the interruption limit of switchgears due to increasing the rate of breakdown by the metal vapors between the electrodes.