터보 분자 펌프(Turbomolecular pump)내의 자유 분자 유동에 관한 수치 해석적 연구

황영규,허중식,Hwang, Y.K.,Heo, J.S. 대한설비공학회 1996 설비공학 논문집 Vol.8 No.2

In the free molecular flow range, the pumping performance of a turbomolecular pump has been predicted by calculation of the transmission probability employing the integral method and the test particle Monte-Carlo method. The velocities of molecules incident upon a moving blade are given by the random numbers, which are sampled from the Maxwell molecular velocity distribution function. The present results agree quantitatively with the previous known numerical results. For a multi-stage pump, the velocity profile of molecules between two blade rows is not Maxwell distribution. In this case, the Monte-Carlo method is employed to calculate the overall transmission probability for the entire set of blade rows. When the results of the approximate method combining the single stage solutions are compared with those of the Monte-Carlo method for the pump having six rows at C=0.6, the approximate method overestimates as much as 36% in the maximum compression ratio and 19% in the maximum pumping speed than does the Mote-Carlo method.

원판형 드래그펌프의 배기특성에 관한 연구

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)

Selective hydrogenation of levulinic acid to g-valerolactone over carbon-supported noble metal catalysts

황영규,Pravin P. Upare,Jong-Min Lee,Dong Won Hwang,Shiva B. Halligudi,장종산 한국공업화학회 2011 Journal of Industrial and Engineering Chemistry Vol.17 No.2

Selective hydrogenation of biomass derived levulinic acid (LA) to g-valerolactone (GVL) has been efficiently catalyzed by Ru, Pt and Pd noble metal supported on carbon under vapor phase in a continuous down flow fixed-bed reactor system. Among the catalysts, 5 wt.% Ru/C gave GVL with 100%selectivity at 100% LA conversion up to 240 h (10 days) without loss in its activity. The higher catalytic activity and product selectivity of 5 wt.% Ru/C catalyst has been attributed to the higher dispersion of metallic Ru over carbon in nano-sizes compared to Pt and Pd catalysts.

안쪽축이 회전하는 환형관내 헬리컬 유동장의 실험적 연구

황영규,김영주,Hwang, Young-Kyu,Kim, Young-Ju 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.6

This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure drops and skin-friction coefficients have been measured for the fully developed flow of water and that of glycerine-water solution (44%) at a inner cylinder rotational speed of $0{\sim}600$ rpm, respectively. The transitional flow has been examined by the measurement of pressure drops and the visualization of flow field, to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients and to understand the flow instability mechanism. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure drops and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually declined for turbulent flow regime. Consequently, the critical (axial-flow) Reynolds number decreases as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the excitation of taylor vortices.

순수한 찬물속에 잠겨있는 경사진 등온벽면 부근의 자연대류에 관한 수동력학적 안정성

황영규,장명륜,Hwang, Y.K.,Jang, M.R. 대한설비공학회 1990 설비공학 논문집 Vol.2 No.4

Hydrodynamic stability equations are formulated for natural convection flows adjacent to a heated or cooled, inclined, isothermal surface in pure water at $4^{\circ}C$, where the density variation with temperature becomes nonlinear. The resulting stability equations, when reduced to ordinary differential equations by a similarity transformation, constitute a two-point boundary-value problem, which was solved numerically. It is found from the obtained stability results that the neutral stability curves are systematically shifted to have lower critical Grashof numbers, as the inclination angle of upward-facing plate increases. Also, the nose of the neutral stability curve becomes blunter as the angle increases. It implies that the greater the inclination of the upward-facing plate, the more susceptible of the flow to instability for the wide range of disturbance wave number and frequency.

박막형 플렉시블 전자소자를 위한 전사 인쇄법

황영규,윤종원,고흥조,Hwang, Yeong-Gyu,Yun, Jong-Won,Go, Heung-Jo 한국정보디스플레이학회 2013 인포메이션 디스플레이 Vol.14 No.4

응답계수(應答係數)를 이용(利用)한 건물벽에서의 열부하(熱負荷) 계산(計算)

황영규,박이동,Hwang, Y.K.,Pak, E.T. 대한설비공학회 1988 설비저널 Vol.17 No.4

An application of thermal response coefficient method for obtaining thermal load on stud-frame walls in a typical house is presented. A set of stud-frame walls is two-dimensional heat conduction transients with composite structure. The ambient temperature on the right-hand face of the stud-frame walls is a typical day-cycle input and the room temperature on the left-hand face is a constant input. The desired output is thermal load at the left-hand face. The time-dependent ambient temperature is approximated by a continuous, piecewise-linear function each having one hour interval. The conduction problem is spatially discretized as 8 computer modelings by finite elements to obtain thermal response coefficients. The discretization and round-off errors can be neglected in the range of adequate number of nodes. A 60-node discretization is recommended as the optimum model among 8 computer modelings. Several sets of response coefficients of the stud-frame walls are generated by which the rate of heat transfer through the walls or some temperature in the walls can be calculated for different input histories.

예선회가 존재하는 회전유동장의 불안정성 수치해석

황영규,이윤용,이광원,Hwang, Young-Kyu,Lee, Yun-Yong,Lee, Kwang-Won 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.4

The hydrodynamic instability of the three-dimensional boundary-layer over a rotating disk has been numerically investigated for these flows; Ro = -1, -0.5, and 0, using linear stability theory. Detailed numerical values of the disturbance wave number. wave frequency. azimuth angle. radius (Reynolds number, Re) and other characteristics have been calculated for the pre-swirl flows. On the basis of Ekman and Karman boundary layer theory, the instability of the pre-swirl flows have been investigated for the unstable criteria. The disturbance will be relatively fast amplified at small fe and within wide bands of wave number compared with previously known Karman boundary-layer results. The flow (Ro =-0.5) is found to be always stable for a disturbance whose dimensionless wave number is greater than 0.9. It has a larger range of unstable interval than Karman boundary layer and can be unstable at smaller Re.

터보분자펌프의 성능해석에 관한 수치해석적 연구

황영규,허중식,Hwang, Yeong-Gyu,Heo, Jung-Sik 대한기계학회 1996 大韓機械學會論文集B Vol.20 No.11

In the free molecular flow range, the pumping performance of a turbomolecular pump has been predicted by calculation of the transmission probability which employs the integral method and the test particle Monte-Carlo method. Also, new approximate method combining the double stage solutions, so called double-approximation, is presented here. The calculated values of transmission probability for the single stage agree quantitatively with the previous known numerical results. For a six-stage pump, the Monte-Carlo method is employed to calculate the overall transmission probability for the entire set of blade rows. When the results of the approximate method combining the single stage solutions are compared with those of the Monte-Carlo method at dimensionless blade velocity ratio C=0.4, the previous known approximate method overestimates as much as 34% than does the Monte-Carlo method. But, the new approximate method gives more accurate results, whose relative error is 10% compared to the Monte-Carlo method, than does the previous approximate method.

친환경 리모델링 철거공사 프로세스 모델 (벽식구조 노후 공동주택을 대상으로)

황영규,김기현,김경래,한주연,Hwang, Young-Gyu,Kim, Ki-Hyun,Kim, Kyung-Ra,Han, Ju-Yeoun 한국건설관리학회 2008 건설관리 : 한국건설관리학회 학회지 Vol.9 No.6

리모델링 공사는 신축공사와 달리 철거공사가 주공정으로 선행되어야 하는데 현행 철거공사는 개략적 수준의 철거관리계획에 의한 생산성만을 강조한 철거 형태로 인해 폐자재 재활용이 되지않고 있어 자원낭비, 환경파괴를 가중 시키고 있으며, 철거작업 중 작업자의 안전과 구조체의 안전등이 전혀 고려되지 않고 철거하는 것이 현실이다. 따라서 친환경 철거공사가 되기 위해서는 프로세스의 개선이 우선 되어야하며 그 단계를 1) 철거관련 조사분석, 2) 철거관리 도서작성, 3) 철거관리 시공계획서작성, 4) 철거시공 및 감리, 5) 철거 후 관리의 5단계로 구분 하였으며, 특히 철거도면 작성으로 표준철거 WBS가 구축되고, 철거장비 및 공법, 폐기물 투하, 철거공정계획 수립이 가능하며 마감재 철거 후 구조체의 안전점검을 실시하므로써 철거중 불가피한 보수보강이 가능하며, 철거완료 Check list 작성에 따라 리모델링 본공사의 Database 활용이 가능하게 되었다. 본 논문에서는 현행리모델링 철거공사 프로세스(AS-IS)의 문제점을 분석하고 개선된 친환경 리모델링 철거공사 프로세스(TO-BE)를 IDEF0 모델을 사용하여 제안하고자 한다. Demolition work is a precedence activity that is performed earlier than other remodeling activities. And demolition work is one of the critical path activities. So, demolition work is needed for systematic plan and management. However, contractors of the remodeling project established a rough plan and did not consider recycling wastes, safety of workers and structural stable of building. To improve this problem, a eco-friend process model of remodeling project is needed to be established. The process model is composed of five phases; 1) survey and analysis of general condition of demolition work, 2) prepare documents of demolition work 3) establishing demolition work plan, 4) demolition and inspection, 5) post-demolition management. Especially, demolition documents are based on establishing WBS, selecting the equipment and method, waste management and structure reinforcement. A process model of eco-friend demolition work is developed by using IDEF0 method.