축류압축기 익렬에서의 역류 유동 특성에 대한 수치적 연구

손창현,Sohn, Chang-Hyun,Longley, John Peter 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.5

Numerical simulation is performed with Denton's code to get pressure loss coefficients in wide range of reverse flow incidence(from -90 degree to +85 degree) for an axial compressor cascade. As a results, it is found that the pressure loss coefficient is increased with incidence and there exist critical incidence which corresponds to the maximum pressure loss coefficient. Pressure loss coefficient with bigger incidence than its critical value is decreased. The effect of increasing incidence in a cascade extremely reduce the mass flow rate by the large flow separation region. Consequently this effect reduce the portion of dynamic pressure in the total pressure loss and beyond the critical incidence the pressure loss coefficient decrease.

극초음속 유동장의 경계층 해석

손창현,최승,문수연,김재영,이열화,Sohn Chang-Hyun,Choi Seung,Moon Su-Yuon,Kim Jae-Yung,Lee Yul-Hwa 한국군사과학기술학회 2004 한국군사과학기술학회지 Vol.7 No.3

Matching inviscid and boundary layer methods are developed for analysis of hypersonic flow with thick boundary layer. The new equations match all the boundary layer properties with a variation in the inviscid solution near the edge, except for the normal velocity. Computational comparison are peformed for incompressible and compressible flows over a flat plate. Results from the present method are compared with Wavier-Stokes solutions. The present results are in good agreement with Wavier-Stokes solutions. They show that the new technique can provide improved predictions of heating rates and skin friction predictions for preliminary design of vehicles where shear layers and entropy layer swallowing are importantfor for preliminary design.

튜브형상에 따른 배기가스 재순환 냉각 장치 열전달 성능 평가

손창현,Sohn, Chang-Hyun 한국자동차공학회 2007 한국 자동차공학회논문집 Vol.15 No.5

With the Euro-4 regulation coming into effect, the domestic car industry is forced to look for newer options to reduce NOX in the exhaust. EGR(Exhaust Gas Recirculation) Cooler is an effective method for the reduction of NOX form a diesel engine. High efficiency, low pressure loss and compactness are desirable features of an EGR Cooler. The cooling performance of EGR depends on the shape of tubes and the location of the entrance and exit. This paper reports the computational work conducted to estimate the performance of EGR cooler with three different cross section tubes and a triangular spiral tube. Three dimensional computation results show that the triangular tube is more effective than circular and rectangular tube. The most effective geometry is a triangular spiral tube with offset inlet and outlet locations.

부력의 영향을 포함한 점탄성 유체의 열전달에 관한 수치해석

손창현,안성태,장재환,Sohn, Chang-Hyun,Ahn, Seong-Tae,Jang, Jae-Hwan 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.4

The present numerical study investigates flow characteristics and heat transfer enhancement of the viscoelastic non-Newtonian fluid in a 2:1 rectangular duct. The combined effect of temperature-dependent viscosity, buoyancy and secondary flow caused by second normal stress difference are all considered. The Reiner-Rivlin model is used as a viscoelastic fluid model to simulate the secondary flow and temperature-dependent viscosity model is adopted. Three types of thermal boundary conditions involving different combinations of heated walls and adiabatic walls are considered in this study. Calculated Nusselt numbers are in good agreement with experimental results in both the thermal developing and thermally developed regions. The heat transfer enhancement can be explained by the combined viscoelasticity-driven secondary flow, buoyancy-induced secondary flow and temperature-dependent viscosity.

유선좌표계를 사용한 이차원 익형의 실속에 대한 부분포물형 Navier-Stokes 해석(Ⅱ)

손창현(Chang-Hyun Sohn),최도형(Do-Hyung Choi) 한국항공우주학회 1994 韓國航空宇宙學會誌 Vol.22 No.2

열전달 향상을 위한 새로운 MCFC 연료전지용 프리컨버터의 수치해석

손창현(Chang Hyun Sohn) 대한기계학회 2013 大韓機械學會論文集B Vol.37 No.8

본 연구는 MCFC용 벽면가열 방식 프리컨버터의 낮은 열전도율 때문에 발생하는 벽면 고온 발생 문제를 해결하기 위한 두 가지 방안을 수치해석을 통해 연구하였다. 프리컨버터 내부에 열전도율이 높은 다공성판을 설치한 경우 벽면에서 중심부위로 열전달이 향상되어 수소 생성이 벽면부위에 국한되지 않고 촉매내부에 좀 더 균일하게 발생되는 것을 확인하였다. 그리고 촉매 내부에 일정한 두께의 빈 공간을 중심, 1/2 그리고 4/5 위치에 두고 해석하여 결과를 비교하였고, 1/2위치의 빈 공간이 다른 경우에 비해 연료전환이 보다 이상적인 경우에 근접하지만 열전도율이 높은 다공성판의 설치가 보다 효과적임을 확인하였다. In this study, two proposals for the wall heating preconverter of an MCFC are numerically studied to resolve hot temperature generation near the wall by the low thermal conductivity of the catalyst. The numerical results show that the inserted porous cupper plates on the catalyst evidently improve heat transfer and realize more uniform reforming in the preconverter. The calculated results for the preconverter with a circumference empty space of catalyst located at center, 1/2 and 4/5 from center line are compared. The circumference empty space located at 1/2 position shows better results than other cases, but the positive effect on the uniform reforming process is less than in the case of inserted cupper porous plates on the catalyst.

직사각형 덕트에서 Reiner-Rivlin 유체의 이차유동 및 열전달에 관한 수치해석

정석호,손창현,신세현,Jung, Suk Ho,Sohn, Chang Hyun,Shin, Sehyun 대한기계학회 1998 大韓機械學會論文集B Vol.22 No.9

The present numerical study investigates the effect of a secondary flow on the heat transfer in order to delineate the mechanism of laminar heat transfer enhancement of a viscoelastic fluid in rectangular ducts. The second normal stress generating a secondary flow is modeled by adopting the Reiner-Rivlin constitutive equation and the calculated secondary flow showed good agreement with experiments. The primary velocity U as well as the pressure drop were not affected by the secondary flow in rectangular ducts, whose order of magnitude is less than 0.1% of the primary velocity. The small magnitude of the secondary flow, however, affect moderately the temperature fields. The calculated Nusselt numbers with secondary flow show 50% heat transfer enhancement over those of a purely viscous non-Newtonian fluid, which are considerably lower than the experimental values. Therefore, we conclude that there should be an additional heat transfer enhancement mechanism involved in the viscoelastic fluid such as temperature-dependence.

MCFC용 개질기 및 프리컨버터의 수치연구

변도현(Do-Hyun Byun),손창현(Chang-Hyun Sohn) 한국전산유체공학회 2011 한국전산유체공학회지 Vol.16 No.1

In this paper, various operating parameters of stream reforming process from methane in stream reformer and preconverter for MCFC is studied by numerical method. Commercial code is used to simulated the porous catalyst with user subroutine to model three dominant chemical reactions which are Stream Reforming(SR), Water-Gas Shift(WGS), and Direct Stram Reforming(DSR). The hydrogen production is tested with different wall temperature and different reactor shapes. The calculated results of the concentration of hydrogen in stream reformer are very well consistent with experimental results. This numerical study gives the design reactor wall temperature condition and size of reactor to satisfy the required fuel conversion.

MCFC 프리컨버터 촉매의 열전도특성과 연료전환율 해석

변도현(Do Hyun Byun),손창현(Chang Hyun Sohn) 대한기계학회 2012 大韓機械學會論文集B Vol.36 No.4

본 연구에서는 비상시 전기 공급용 MCFC 프리커버터의 천연가스(메탄)로부터 수소의 생산량을 증가시키는 경우를 수치적으로 해석하였다. 상용 코드를 사용하였으며 촉매는 다공성 매질로 시뮬레이션 하였다. 3가지 주요 화학반응인 수증기 개질반응(SR), 수성 가스 전환(WGS) 및 직접 수증기 개질 반응(DSR)은 사용자 부프로그램을 사용하여 해석하였다. 프리컨버터에서 10%의 연료전환율을 얻기 위해 요구되는 추가 열량을 벽면을 통해 공급하게 되면 프리컨버터의 벽면 부근에서만 매우 불균일한 온도분포와 화학반응이 일어나는 것으로 분석되었다. 이와 같은 현상은 매우 작은 열전도율을 갖는 다공성 매질의 촉매와 흡열반응으로 설명되어질 수 있다. 해석결과 프리컨버터의 길이가 짧은 경우가 보다 균일한 연료전환율을 보여 주며, 촉매의 유지 보수 면에도 길이가 짧은 경우가 유리함을 보여 주었다. In this study, a preconverter of an MCFC for an emergency electric power supplier is numerically simulated to increase the hydrogen production from natural gas (methane). A commercial code is used to simulate a porous catalyst with a user subroutine to model three dominant chemical reactions-steam reforming, water-gas shift, and direct steam reforming. To achieve a fuel conversion rate of 10% in the preconverter, the required external heat flux is supplied from the outer wall of the preconverter. The calculated results show that the temperature distribution and chemical reaction are extremely nonuniform near the wall of the preconverter. These phenomena can be explained by the low heat conductivity of the porous catalyst and the endothermic reforming reaction. The calculated results indicate that the use of a compact-size preconverter makes the chemical reaction more uniform and provides many advantages for catalyst maintenance.

MCFC용 프리컨버터 수증기 개질반응의 수치연구

변도현(Do-Hyun Byun),손창현(Chang-Hyun Sohn) 한국전산유체공학회 2010 한국전산유체공학회 학술대회논문집 Vol.2010 No.5

In this paper, various operating parameters of stream reforming process from methane in preconverter for MCFC is studied by numerical method. Commercial code is used to simulated the porous catalyst with user subroutine to model three dominant chemical reactions which are Stream Reforming(SR), Water-Gas Shift(WGS), and Direct Stram Reforming(DSR). The hydrogen production is tested with different wall temperature, Gas Hourly Space Velocity(GHSV), and different reactor shapes.