• 대한안전경영과학회지
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• 제4권2호
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• pp.237-249
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• 2002

A cutting fluid can improve machining quality and tool life by maintaining the tool toughness and by providing a lubrication effect to reduce the friction between the chip and tool interface. Although liquid nitrogen as an environmentally safe coolant has been widely recognized in cryogenic machining, its function as a lubricant is plausible due to its chemical inertness, physical volatility and low viscosity. Since a reduced friction is a direct witness of the lubrication effect from a tribological viewpoint, this paper presents an evaluation of the apparent friction coefficient on the tool-chip interface in cryogenic cutting operations to prove and characterize the lubricity of LN2 in cryogenic machining. The mathematical approaches have been formulated to derive the normal and frictional forces on the tool-chip interface for the oblique cutting tests.

• 한국추진공학회지
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• 제26권6호
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• pp.10-20
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• 2022

본 연구에서는 케로신 다단연소사이클 엔진용 예연소기를 설계하기 위해, 고압의 산화제 과잉 조건에서 예연소가스를 계산하고 냉각유로에서 극저온 유체의 복합열전달 및 수력 특성을 해석할 수 있는 설계코드를 개발하였다. 사용자 편의성과 범용성을 가진 오픈 소스 라이브러리 Cantera를 활용하였으며, 실제유체의 열역학/전달 상태량을 정확히 계산하기 위해 관련 소스 코드들을 새로 작성하여 Cantera에 추가하였다. 현재 예비설계 중인 100톤급 부스터 엔진용 예연소기에 적용하였으며, CFD 해석결과와 비교를 통해 설계코드로서의 예측 정확도와 활용성을 확인하였다.

• 설비공학논문집
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• 제12권9호
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• pp.825-834
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• 2000

A heat exchanger analysis is performed to investigate the heating characteristics of cryogenic nitrogen by ambient air for the purpose of cryogenic automotive propulsion. The heat exchanger is a concentric triple-passage for supercritical nitrogen, and the radial fins are attached on the outermost tube for the crossflow of ambient air. The temperature distribution is calculated for the nitrogen along the passage, including the real gas properties of nitrogen, the fluid convections and the conductions through the tube walls and the fins. Since the wall temperature of the outer (ambient side) tube is very low in most cases, a heavy frost can be formed on the surface, affecting the heat exchange performance. By the method of the similarity between the heat and the mass transfer of moist air, the frost growth and the time-dependent effectiveness of the heat exchanger are calculated for various operating conditions. It is concluded that the frost formation can augment the heating of nitrogen during the initial period because of the latent heat, then gradually degrades the heat exchange because of the increased thermal resistance. Practical design issues are discussed for the flow rate of nitrogen, the velocity and humidity of ambient air, and the sizes of the fin.

• 한국전산유체공학회지
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• 제18권2호
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• pp.17-25
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• 2013

The process of flow through porous media is of interest a wide range of engineering fields and areas, and the importance of fluid flow with a change in phase arises from the fact that many industrial processes rely on these phenomena for materials process, energy transfer. Especially, the flow phenomena of cryogenic liquid subjected to evaporation is of interest to investigate how the cryogenic liquid behaves in the porous structure. In this study, thermo physical properties, morphological properties of the glass wool with different bulk densities in terms of its temperature-dependence and permeability behaviors under different applying pressure are discussed. Using the experimentally determined properties, characteristics of two main experimental results are investigated. In addition, simulation results are used to realize the cryogenic liquid's flow in porous media, and are compared with experimental results. By using the experimentally determined properties, more reasonable results can be suggested in dealing with porous media flow.

• 한국초전도ㆍ저온공학회논문지
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• 제18권1호
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• pp.64-68
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• 2016

High Temperature Superconductor power cable systems are being developed actively to solve the problem of increasing power demand. With increases in the unit length of the High Temperature Superconductor power cable, it is necessary to develop highly efficient and reliable cryogenic pumps to transport the coolant over long distances. Generally, to obtain a high degree of efficiency, the cryogenic pump requires a high pressure rise with a low flow rate, and a partial emission type pump is appropriate considering its low specific speed, which is different from the conventional centrifugal type, full emission type. This paper describes the design of a partial emission pump to circulate subcooled liquid nitrogen. It consists of an impeller, a circular case and a diffuser. The conventional pump and the partial emission pump have different features in the impeller and the discharge flow passage. The partial emission pump uses an impeller with straight radial blades. The emission of working fluid does not occur continuously from all of the impeller channels, and the diffuser allows the flow only from a part of the impeller channels. As the area of the diffuser increases gradually, it converts the dynamic pressure into static pressure while minimizing the loss of total pressure. We used the known numerical method for the optimum design process and made a CFD analysis to verify the theoretical performance.

• 드라이브 ㆍ 컨트롤
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• 제12권4호
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• pp.1-7
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• 2015

In this study, a spiral valve which is used with a cryogenic linear expander and composed of plural plate coil shapes was examined. Generally, a spiral valve is well known for having excellent efficiency and low noise characteristics. In order to determine the movement characteristics and to investigate the limit of valve displacement, the stress variations according to the changes of operating pressure, displacement and workable temperature are discussed. From this examination, it is considered that the results of this study will significantly facilitate the design and development of a spiral valve for the cryogenic linear expander.

• 한국수소및신에너지학회논문집
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• 제35권2호
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• pp.146-151
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• 2024

The demand for research on materials with excellent cryogenic strength and ductility has been increasing, particularly for applications such as liquid hydrogen (20 K) storage tanks. To effectively utilize liquid hydrogen, a system capable of maintaining and operating at 20 K is essential. Therefore, preliminary research and verification of the cooling system are crucial. In this study, a heat transfer analysis was conducted on a cooling system to meet the cryogenic environment requirements for cryogenic hydrogen chamber, which are conducted at liquid helium temperatures (4 K). The cooling mechanism in a helium cooling system was examined using numerical analysis. The numerical cooling trends were compared with experimentally obtained cooling results. The good agreement between numerical and experimental results suggests that the numerical approach developed in this study is applicable over a wide range of cryogenic systems.

• 한국분무공학회지
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• 제15권4호
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• pp.182-188
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• 2010

Significant real fluid behaviors including rapid property changes take place where high pressure combustion devices such as rocket engines. The flamelet model is the reliable approach to account for the real fluid effects. In the present study, the flamelet equations are extended to treat the general fluids over transcritical and supercritical states. The real fluid flamelet model is carried out for the gaseous hydrogen and cryogenic liquid oxygen flames at the wide range of thermodynamic conditions. Based on numerical results, the precise discussions are made for effects of real fluid, pressure, and differential diffusion on the local flame structure.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2004년도 하계학술발표 논문집
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• pp.45-45
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• 2004

• 한국항공우주학회지
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• 제41권10호
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• pp.833-839
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• 2013

위성체는 지상에서 우주환경시험을 거쳐 기능 및 작동상태를 점검해야 하며, 이를 위해서는 우주환경을 모사 할 수 있는 우주환경 모사장비가 필요하다. 위성체 및 위성체의 부품 성능을 검증하기 위해 사용되는 열진공 챔버는 진공용기, 진공시스템, 열제어 시스템 등으로 구성이 된다. 특히, 고온 및 극저온의 열환경을 모사하는 열제어 시스템이 열진공 챔버의 핵심이라고 할 수 있으며, 열제어 시스템의 성능은 극저온 블로워의 성능에 의해 결정된다. 본 논문에서는 극저온 블로워의 유동 해석과 블레이드의 구조해석을 통해 원심팬을 설계 하였으며, 구동부와 유체부의 열전달 방지를 위한 열장벽, 모터의 과열 방지를 위한 냉각 시스템 등이 설계되었으며, 이는 열해석을 통해 검증 되었다. 최종적으로 성능실험을 수행하여 극저온 블로워의 성능을 확인하였다.