• Journal of the KSME
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• v.30 no.6
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• pp.548-554
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• 1990

대체에너지 기관으로서 요구되는 조건을 갖춘 스터링엔진의 이해를 돕기 위하여 기본원리, 개 발현황, 개발상 문제점 등의 기본사항을 소개하였다. 내연기관과는 달리 외연기관인 스터링엔 진은 작동유체가 밀폐공간 내에서 고. 저온 양 영역을 이동하면서 압력차를 발생시켜 일을 형성 하는 과정을 밟기 때문에 고온. 고압일수록 높은 출력이 예상되며, 전열성능과 작동저항면에서 수소나 헬륨과 같은 저분자량의 가스가 작동체로 채택되기 때문에 작동유체의 누기(leakage) 및 크랑크실의 냉각 윤활유의 작동공간으로의 누유 등은 스터링엔진의 출력 저하에 가장 큰 요인 으로 작용한다. 마찰 등 기계적 손실의 저감기술, 속도제어기술, 용도에 따른 엔진 형식 설계 기술, 구성부품 성능향상을 위한 요소기술 등의 개발이 중요한 과제가 되고 있으며, 이상 소개한 내용이 관심있는 많은 분들의 스터링엔진 연구나 이해에 도움이 될 수 있기를 바란다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.207-213
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• 1990

Natural convection heat transfer in rectangular air enclosure was studied interferometrically and numerically for the use of adiabatic and constant temperature horizontal boundary conditions. In the isothermal horizontal boundary case with the temperature difference ratio, .DELTA. $T_{v/}$.DELTA. $T_{H}$ .simeq. 1 temperature distribution in the enclosure is strongly stratified and the average Nusselt Number is higher than that of adiabatic horizontal boundary case.ase.

• Journal of Power System Engineering
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• v.5 no.1
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• pp.27-34
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• 2001

관 외벽에 낮은 핀을 가진 수직 및 경사 열사이폰의 열전달 성능에 관한 실험적인 연구를 하였다. 관 외벽에 낮은 핀을 가진 이상밀폐 열사이폰의 열전달 성능을 비교 분석하기 위하여 동일한 규격의 평관에서도 실험적인 연구를 하였다. 작동유체는 증류수와 CFC-30을 사용하였다. 열사이폰의 경사각과 자동온도를 변화시키면서 실험한 결과 경사각의 변화에 따라 열사이폰의 열전달 성능은 큰 변화를 나타내었다. 그리고 평관으로 제작한 열사이폰보다 관 외벽에 낮은 핀관을 가진 동관으로 제작한 열사이폰의 열전달 성능이 높게 나타났다. 그리고 열사이폰의 경사각이 $20{\sim}50^{\circ}$ 범위에서 열전달 성능이 높게 나타났다.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.16 no.2
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• pp.194-203
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• 1987

A numerical study has been conducted on the combined radiation-natural convection heat transfer characteristics in a square cavity with a selectively transparent wall. The fluid in the cavity is assumed to be transparent to the thermal radiation. The effect of the wall emissivity is mainly considered in view of the temperature and flow fields. The comparison of the radiative heat flux and conductive heat flux variations along the isothermal wall is presented as well. The results show that the Nusselt number distribution is fairly uniform due to the com-pensative interaction of the radiation and convection heat transfer.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.6
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• pp.750-756
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• 1985

Experimental investigation was carried out to study the natural convection of water and silicon oil due to end temperature differences in a horizontally insulated rectangular enclosure of aspect ratio 0.1 with a special attention on the core configuration in the laminar boundary-layer flow regime. Rayleigh number ranges covered herein are Ra=4.40 * 10$^{6}$ -9.64 * 10$^{7}$ for water and Ra=1.69*10$^{5}$ -3.80*10$^{6}$ for silicon oil, respectively. In the case of water, for Ra.geq.2.21 * 10$^{7}$ there appeared distinct horizontal thermal layers adjacent to the horizontal boundaries in the core and the temperature distribution outside the horizontal thermal layers, i.e., in the mid-core region, is vertically stratified. The core flow pattern was shown to be nonparallel with a weak back flow in the mid-core for Ra.geq.3.63 *10$^{7}$ . In the case of silicon oil, distinct horizontal thermal layers appeared along the core horizontal boundaries for Ra.geq.1.27 * 10$^{6}$ with a stratified temperature distribution in the mid-core, but the core flow pattern in this case was shown to be parallel. In addition, secondary flow appeared near the hot wall for Ra.geq.3.80 * 10$^{6}$ . Nusselt number, Nu, was found to be proportional to R $a^{0.3}$ for water and R $a^{0.28}$ for silicon oil in the boundary-layer flow regime. There also in an indication from the comparison with other results that Nu is independent of aspect ratio for water in the boundary-layer flow regime in low aspect ratio enclosures.res.

• Aerospace Engineering and Technology
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• v.1 no.1
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• pp.163-172
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• 2002

The turbine system composed of a nozzle and a rotor is used to drive turbopumps while gas passes through the nozzle, potential energy is converted to kinematic energy, which forces the rotor blades to spin. In this study, an aerodynamic design of a turbine system is investigated using compressible fluid dynamic theories with some pre-determined design requirements (i.e.,pressure ratio, rotational speed, required power etc.) obtained from a liquid rocket engine (L.R.E.) system design. For simplicity of a turbine system, impulse-type rotor blades for open type L.R.E. have been chosen. Usually, the open-type turbine system requires low mass flow rate compared to the close-type system. In this study, a partial admission nozzle is adopted to maximize the efficiency of the close-type turbine system. A design methodology of the a turbine system has been introduced. Especially, a partial admission nozzle has been designed by means of simple empirical correlations between efficiency and configuration of the nozzle. Finally, a turbine system design for a 10 ton thrust level of L.R.E is presented.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1080-1085
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• 2004

The physical model considered here is a horizontal layer of fluid heated below and cold above with heat-generating conducting body placed at the center of the layer. The dimensionless thermal conductivities of body considered in the present study are 0.01, 1 and 150. The dimensionless temperature difference ratios considered are 0.25, 2.5 and 25. Two-dimensional solution for unsteady natural convection is obtained using an accurate and efficient Chebyshev spectral methodology for variety of Rayleigh number from $10^{3}$ to $10^{6}$. Multi-domain technique is used to handle square-shaped heat-generating conducting body. The results for the case of conducting body with heat generation are also compared to those without heat generation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.10
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• pp.3272-3281
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• 1996

The flow analysis method which had been developed for the numerical calculation of 3-dimensional, incompressible and turbulent flow within an axial compressor was extended to the flow field within centrifugal impeller. In this method based on the SIMPLE(Semi Implicit Method Pressure Linked Equations) algorithm, the coordinate transformation was adopted and the standard k-.epsilon. model using wall function was used for turbulent flow analysis. The calculated flow fields have agreed very well with measurement results. Especially, 3-dimensional and viscous flow characteristics including secondary flows, jet-wake flow and decreased pressure rise along impeller passage, which can't be predicted by inviscid Q3D calculation were predicted very reasonably.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.3
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• pp.741-750
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• 1995

The turbulent buoyancy-driven flow in 2-dimensional enclosed cavities heated from the vertical side is numerically calculated for both cases of a Rayleigh number of 5*10$^{10}$ for air and 2.5*10$^{10}$ for water. Three different turbulence models are considered : standard k-.epsilon. model of Ozoe and low-Reynolds-number model of Lam and Bremhorst, and another low-Reynolds-number model of Davidson. The results indicate that the use of low-Reynolds number models is recommended for the indoor airflow computation, and the results from Davidson model are reasonably close to the reported experimental data. A sensitivity study shows that the amounts of wall-heat transfer and the velocity profiles with the Lam and Bremhorst model largely depend on the choice of the wall function for .epsilon..

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.11
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• pp.3630-3638
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• 1996

An experimental study has been conducted to explore the behaviors of the radiative ignition of polymethylmetacrylate(PMMA) in a confined enclosure such as the ignition delay time, PMMA surface temperature, the ignition location and the ignition process. In addition, the effects of hot wall orientation on the ignition delay and PMMA surface temperature were studied. When the hot wall is located at the bottom, ignition delay time is the shortest. Ignition surface temperature becomes the lowest for the hot top wall case. These are due to buoyancy effect. Since the radiative heat flux of hot wall is rather lower than laser source, the ignition is considered to be controlled by the mixing process. Therefore, the ignition location, where appropriate mixture of fuel and oxygen exists, occurs near the hot wall. The flame propagates along the hot wall where there exists sufficient oxygen.