• 천문학회보
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• 제36권2호
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• pp.156-156
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• 2011

VPH (Volume Phase Hologram) grating is one of the transmission gratings and is known as its remarkable efficiency (>90%). It has two different densities of gelatins causing interference patterns. The VPH grating is favored in many astronomical instruments these days and also IGRINS, which is up coming near infrared high-resolution spectroscope expected to see the first light next year, uses the VPH grating as its cross-disperser. The infrared astronomical instruments operate at cryogenic temperature (~100K) in order to cut down thermal noise and the optical components of IGIRNS will be operated at 130K. The VPH grating is sandwiched in between fused silica or glass and glued together using optical adhesive. IGRINS is expected to go through 50 times of thermal cycling in 10 years including the performance test and this research is to check whether the physical characteristic such as the adhesion or dichromatic gelatin does not break and change from the several cryogenic thermal cycling. The two identical test gratings provided from Kaiser Optical System, Inc. are used in this test. One VPH grating is cooled down to 100K for 2 hours with maximum dT/dt = 5 and warmed up to the room temperature and another grating is kept stored in the room temperature and used as a control sample. In order to check the change, we inspected the grating with eyes and checked its efficiency and transmission at the room temperature every 10 cycling. From the 40 times of cryogenic temperature cool down cycling, the VPH grating showed no signs of change within the error compared to the control sample. We concluded the VPH grating is durable through several cryogenic thermal cycling.

• Structural Engineering and Mechanics
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• 제25권4호
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• pp.445-466
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• 2007

As the LNG (Liquefied Natural Gas) tank contains cryogenic liquid, realistic thermal analyses are of a primary importance for a successful design. The structural details of the LNG tank are so complicated that some strategies are necessary to reasonably predict its temperature distribution. The proposed heat transfer model can consider the beneficial effects of insulation layers and a suspended deck on temperature distribution of the outer concrete tank against cryogenic conditions simply by the boundary conditions of the outer tank model. To this aim, the equilibrium condition or heat balance in a steady state is utilized in a various way, and some aspects of heat transfer via conduction, convection and radiation are implemented as necessary. Overall thermal analysis procedures for the LNG tank are revisited to examine some unjustifiable assumptions of conventional analyses. Concrete and insulation properties under cryogenic condition and a reasonable conversion procedure of the temperature-induced nonlinear stress into the section forces are discussed. Numerical examples are presented to verify the proposed schemes in predicting the actual temperature and stress distributions of the tank as affected by the cryogenic LNG for the cases of normal operation and leakage from the inner steel tank. It is expected that the proposed schemes enable a designer to readily detect the effects of insulation layers and a suspended deck and, therefore, can be employed as a useful and consistent tool to evaluate the thermal effect in a design stage of an LNG tank as well as in a detailed analysis.

• 한국초전도ㆍ저온공학회논문지
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• 제25권1호
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• pp.6-10
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• 2023

2 K superfluid helium cryogenic system is the crucial component of many large accelerators. When the cryogenic system is operating at 2K@3129Pa, many room-temperature parts are connected to superfluid helium via tubes. Air Leakage in these connections may lead to air contamination of the cryogenic system. Air contamination may cause equipment failure in cryogenic systems and, in extreme cases, render the entire accelerator system inoperable. Helium guard is a technique that guards against air contamination of these sub-atmospheric pressure connections in 2 K superfluid helium cryogenic system. This paper introduces a typical 2 K cryogenic distribution design for large accelerators, and make risk analysis of air contamination. Finally, the analysis of specific leakage points and detailed engineering design are presented, which may be used as a reference when designing of a 2 K superfluid helium cryogenic distribution system.

• 한국분무공학회지
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• 제26권1호
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• pp.18-25
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• 2021

The objective of this study is to investigate the effect of cryogenic intake air temperature on the injected fuel droplet behavior in a compression ignition engine under the different start of energizing timing. To achieve this, the intake air temperatures were changed from -18℃ to 18℃ in steps of 9℃, and the result of fuel evaporation rate, Sauter mean diameter, and equivalence ratio distributions were compared. When the intake air temperature decreased in steps of 9℃, less fuel was evaporated by about 3.33% because the cylinder temperature was decreased. In addition, the evaporated fuel amount was increased with retarding the start of energizing timing because the cylinder temperature raised. However, the difference was decreased according to the retarded start of energizing timing because the cylinder pressure was also increased at the start of fuel injection. The equivalence ratio was reduced by 5.94% with decreasing the intake air temperature. In addition, the ignition delay was expected to longer because of the deteriorated evaporation performance and the reduced cylinder pressure by the low intake air temperature.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.413-418
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• 2008

Flow instability in the rocket turbo pump system can be caused by various reasons such as valve, orifice and venturi, etc. The inception of cavitation, especially in the propellant feeding system, is the primary cause of the mass flow and pressure oscillation due to cyclic formation and depletion of cavitation. Meanwhile, the main propellant in liquid rocket engine is the cryogenic one, which is very sensitive to temperature variation, and the variation of propellant properties caused by thermodynamic effect should be accounted for in the flow analysis. The present study focuses on the formation of cryogenic cavitations by adopting IDM model suggested by Shyy and coworkers. Also, the flow instability was investigated in the downstream of orifice by using a developed numerical code. Calculation results show that cryogenic cavitations can lead to flow instability resulting in mass flow fluctuations due to pressure oscillations. And the prediction of cavitations in cryogenic fluid is of vital importance in designing feeding system of LRE.

• 한국수소및신에너지학회논문집
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• 제34권6호
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• pp.615-622
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• 2023

In this study, the theoretical analysis focused on the quantity of liquid hydrogen required for cooling down to 20 K, as well as the generation of boil-off gas (BOG) from the cooling process of the cryogenic components. The study involved calculating the amount of liquid hydrogen needed to achieve the desired temperature for the cryogenic components and subsequently determining the resulting BOG production at various reference temperatures. It was shown that it was important to efficiently lower the temperature of cryogenic parts through preliminary cooling. As a result, the reference temperature and pressure had an influence on the BOG generation on the cooling of cryogenic components using liquid hydrogen.

• 한국초전도ㆍ저온공학회논문지
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• 제4권1호
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• pp.124-128
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• 2002

A numerical model to obtain the temperature distribution in a radiation shield of cryogenic systems was proposed. Conformal mapping was used to transform the eccentric physical region of the upper plate to the concentric numerical region. The effects of the thickness of the radiation shield, the emissivities of the vacuum chamber and the radiation shield, and the eccentricity between the centers of the upper plate and the contact area with a cryocooler on the maximum temperature difference in a radiation shield were shown.

• 대한기계학회논문집A
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• 제22권2호
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• pp.311-320
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• 1998

The cryogenic fracture behaviors of austenitic stainless steel HN2 developed for nuclear fusion reactor were evaluated quantitatively by using the small punch(SP) test. The electrochemical polarization test was applied to study thermal aging degradation of HN2 steel. The X-ray diffraction(XRD) analysis was conducted to detect carbides and nitrides precipitated on the grain boundary of the heat treated HN2 steel. The mechanical properties of the HN2 steel significantly decreased with increasing time and temperature of heat treatment or with decreasing testing temperature. The integrated charge(Q) obtained from electrochemical polarization test showed a good correlation with the SP energy(ESP) obtained by means of SP tests. From the results observed in the x-ray diffraction and anodic polarization curve, it was known that the material the grain boundary. Combining SP test and electrochemical polarization test, it could be useful tools to non-destructively evaluate the cryogenic fracture behaviors and the aging degradation for cryogenic structural material.

• 한국항공우주학회지
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• 제35권3호
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• pp.248-252
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• 2007

본 연구는 공급계 관에서 극저온 연료의 일부가 기화될 경우에 로켓엔진이 지속적으로 작동될 수 있는지의 여부를 묻는 문제와 관련되어 있다. 유동장 내에 증기가 발생하는 것을 모사하는 실험의 결과분석으로 관내의 압력조건에서 극저온 유체의 온도가 포화온도보다 낮을 경우 발생된 증기가 완전히 응축될 수 있다는 것을 확인하였다. 극저온 유체의 정상유동에서 비평형 응축영역을 계산하기 위한 경험관계식을 무차원형태로 구하였고, 이 경험관계식이 실제적으로 활용 될 수 있는 분야를 제시하였다.

• 한국추진공학회지
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• 제9권3호
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• pp.66-73
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• 2005

액체로켓 추진시스템에서 가압시스템은 발사체 추진제 탱크의 얼리지 공간에 제어된 가스를 공급하는 것이다. 가압시스템에서 고온 가스 열교환기를 적용하는 데는 가압제의 비체적을 증가시켜 전체 발사체 시스템의 중량을 감소시키는 장점이 있다. 가압시스템 성능에 있어서 주목할 만한 개선점은 극저온 시스템에서 얻어질 수 있다. 이러한 경우 가스 공급은 극저온 탱크 내부에 저장되어 진다. 본 연구에서는 극저온 추진제를 모의(模擬)하기 위하여 액체 질소를 사용하였다. 극저온 가압제의 온도 특성은 가압시스템에서 구성 단품을 개발하는데 있어서 매우 중요하다. 본 연구에서는 SINDA/FLUINT를 이용한 이론적 해석과 PTF에서 수행된 실험 결과에 대하여 비교 분석이 수행되었다.