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윤현기(Hyungi Yoon),최범석(Beomsuok Choi),박준영(Junyeong Park),안국영(Gukyeong Ahn) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
A metal diaphragm compressor has been widely used for supplying a high pressure hydrogen gas to a hydrogen gas station. A non-return discharge valve is an one component of the compressor that draws off the compressed hydrogen gas. Thos component is self-actuated by differential pressures. Therefore, the rapid response and the less static pressure loss are required. In the present study, to find out the behavior of a valve plunger and static pressure change along the valve, the unsteady flow field has been investigated numerically by using the commercial code CFX. k-w turbulent model, FSI(Fluid Structure Interaction) and mesh deformation are used. Numerical study is conducted for the various pressure differences(△p=0.2, 0.5, 1 and 2bar) between the inlet and outlet of the valve. Significant static pressure drop is observed at the front of the valve plunger because the form of the space between the valve plunger and seat is similar to a convergence nozzle.
전압 리플을 이용해 영전류스위칭하는 두개의 트랜스포머를 가지는 위상천이 풀-브릿지 컨버터
윤현기(Hyun-Ki Yoon),문건우(Gun-Woo Moon),윤명중(Myung-Joong Youn) 전력전자학회 2005 전력전자학술대회 논문집 Vol.- No.-
This paper presents a Zero-Current Switching(ZCS) two-transformer phase-shift full-bridge(TTFB) converter using voltage ripple. The proposed converter provides Zero-Voltage Switching(ZVS) of leading leg switches and ZCS of lagging leg switches using voltage ripple. Especially, circulating current is reduced by ZCS operation and there are no additional components required for the soft switching of power switches. Furthermore, in case of light load, ZVS operation of lagging leg can be achieved. The operations, analysis and design consideration of proposed converter are presented. To verify the validity of the proposed converter, experimental results for a 410W (205V, 2A) prototype are presented.
윤현기(Hyun-Gi Yoon),최원철(Won-Chul Choi),유일수(Il-Soo Yoo) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
Blade parts of the Submersible cargo pump consist of inducer, impeller and diffuser. Suction performance of the inducer is important to ensure the safety operation at low NPSHA. A set of 2-bladed inducers are designed in considerations of the cavitation, head raise and outlet flow angle. At here, total head raise through the inducer is determined based on the NPSHR of the impeller. Diffuser of the submersible cargo pump has a geometrical limit due to its operation conditions. In this study, diffuser is designed based on the performance and geometric characteristics of the existed impeller and outline conditions of the cargo pump. And then, on Suction and hydraulic performance of the one set of the cargo pump are simulated numerically to check its design requirement.
연구용 원자로 수조고온층계통에서의 입구 및 출구 배관 설계
윤현기(H.G. Yoon),서경우(K.W. Seo),박용철(Y.C. Park),지대영(D.Y. Chi) 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.5
The Hot Water Layer System(HWLS) maintains the hot water layer, higher than the average temperature of the pool water, at the upper part of the reactor and service pools so as to minimize the radioactive primary coolant rising up to the pool surface by natural convection in the open pool type research reactor. The ends of the suction and discharge lines ore submerged below the pool surface and located at the same level in the reactor pool. The end shape of the discharge pipe is designed as a T-shape diffuser to distribute the flow uniformly for stable hot water layer formation at the upper section of the reactor and service pools. Heat loss, temperature stratification and velocity boundary layer are taken into consideration to determine the formation of the stable hot water layer through the numerical simulation. Commercial code FLUENT is used to calculate the unsteady pool water flow with different T-shape diffusers and locations of the suction pipe. Also, two kinds of turbulent model, RNG k-e and SST k-w turbulent model, are used for the conservative system design.
윤현기(Hyungi Yoon),박무룡(Mooryong Park),유일수(Ilsu Yoo),황순찬(Soonchan Hwang) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
The operating cost is highly affected by a small difference of pump efficiency around 1~2% in a high capacity pump. So, the detailed revision of the design is required. In the present study, the pump performance has been investigated experimentally and numerically with a change of a stagger angle. The axis of rotation of the stagger angle is placed at the center of the sectional area of the blade between the hub and shroud. The stagger angle is set as -2, -1, 1 and 2 degree from the original design. Performance analysis of each stagger angle is achieved with various flow rates. Cavitation characteristic is also studied at this time. The impeller and diffuser have been investigated numerically by using the commercial code CFX, k-w based SST turbulent model, homogeneous flow model and Rayleigh Plesset cavitation model. It shows good performance that the stagger angle is one degree. Its performance is very similar with the original design near the design point, but better than 2~3% at the high flow rate. The result of the cavitation characteristicshows that the net positive section head (NPSH) is lower than 10% compared with the original design.