• 한국수소및신에너지학회논문집
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• 제26권2호
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• pp.105-113
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• 2015

In order to accelerate hydrogen society in current big renewable energy trend, it is very important that hydrogen can be transported and stored as a fuel in efficient and economical fashion. In this perspective, liquid hydrogen can be considered as one of the most prospective storage methods that can bring early arrival of the hydrogen society by its high gravimetric energy density. In this study, a small-scale hydrogen liquefier has been designed and developed to demonstrate direct hydrogen liquefaction technology. Gifford-McMahon (GM) cryocooler was employed to cool warm hydrogen gas to normal boiling point of hydrogen at 20K. Various cryogenic insulation technologies such as double walled vacuum vessels and multi-layer insulation were used to minimize heat leak from ambient. A liquid nitrogen assisted precooler, two ortho-para hydrogen catalytic converters, and highly efficient heat pipe were adapted to achieve the target liquefaction rate of 1L/hr. The liquefier has successfully demonstrated more than 1L/hr of hydrogen liquefaction. The system also has demonstrated its versatile usage as a very efficient 150L liquid hydrogen storage tank.

• 대한기계학회논문집A
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• 제34권9호
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• pp.1217-1225
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• 2010

소듐을 냉각재로 사용하는 고속로의 증기발생기에서는 소듐과 물의 화학적 반응을 최소화하는 것이 중요한 문제이다. 소듐과 물의 반응 가능성을 줄여 증기발생기의 신뢰성을 향상시키기 위한 한가지 방안으로 이중벽관을 전열관으로 사용하는 증기발생기를 개발하고 있다. 이 증기발생기에서 중요한 현안은 이중벽관에서의 열전달 성능을 향상시키는 문제와 원자로 운전 중에 소듐과 물 반응사고가 일어나기 전에 전열관의 파손을 감지하는 기술을 개발하는 것이다. 이 논문에서는 이 현안을 극복할 수 있는 방안을 제시하였고, 이 기술을 활용하여 증기발생기의 개념을 설계하였다. 또한 이 개념에 적용되는 이중벽관을 설계 및 예비 제작하여 기계적 시험을 수행하였다.

• Nuclear Engineering and Technology
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• 제47권6호
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• pp.700-711
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• 2015

Sodium-cooled fast breeder reactors use liquid sodium as a moderator and coolant to transfer heat from the reactor core. The main hazard associated with sodium is its rapid reaction with water. Sodium-water reaction (SWR) takes place when water or vapor leak into the sodium side through a crack on a heat-transfer tube in a steam generator. If the SWR continues for some time, the SWR will damage the surface of the defective area, causing it to enlarge. This self-enlargement of the crack is called "self-wastage phenomena." A stepwise numerical evaluation model of the self-wastage phenomena was devised using a computational code of multicomponent multiphase flow involving a sodium-water chemical reaction: sodiumwater reaction analysis physics of interdisciplinary multiphase flow (SERAPHIM). The temperature of gas mixture and the concentration of NaOH at the surface of the tube wall are obtained by a numerical calculation using SERAPHIM. Averaged thermophysical properties are used to assess the local wastage depth at the tube surface. By reflecting the wastage depth to the computational grid, the self-wastage phenomena are evaluated. A two-dimensional benchmark analysis of an SWAT (Sodium-Water reAction Test rig) experiment is carried out to evaluate the feasibility of the numerical model. Numerical results show that the geometry and scale of enlarged cracks show good agreement with the experimental result. Enlarged cracks appear to taper inward to a significantly smaller opening on the inside of the tube wall. The enlarged outer diameter of the crack is 4.72 mm, which shows good agreement with the experimental data (4.96 mm).

• Nuclear Engineering and Technology
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• 제39권3호
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• pp.193-206
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• 2007

The Korea Atomic Energy Research Institute has developed an advanced fast reactor concept, KALIMER-600, which satisfies the Generation IV reactor design goals of sustainability, economics, safety, and proliferation resistance. The concept enables an efficient utilization of uranium resources and a reduction of the radioactive waste. The core design has been developed with a strong emphasis on proliferation resistance by adopting a single enrichment fuel without blanket assemblies. In addition, a passive residual heat removal system, shortened intermediate heat-transport system piping and seismic isolation have been realized in the reactor system design as enhancements to its safety and economics. The inherent safety characteristics of the KALIMER-600 design have been confirmed by a safety analysis of its bounding events. Research on important thermal-hydraulic phenomena and sensing technologies were performed to support the design study. The integrity of the reactor head against creep fatigue was confirmed using a CFD method, and a model for density-wave instability in a helical-coiled steam generator was developed. Gas entrainment on an agitating pool surface was investigated and an experimental correlation on a critical entrainment condition was obtained. An experimental study on sodium-water reactions was also performed to validate the developed SELPSTA code, which predicts the data accurately. An acoustic leak detection method utilizing a neural network and signal processing units were developed and applied successfully for the detection of a signal up to a noise level of -20 dB. Waveguide sensor visualization technology is being developed to inspect the reactor internals and fuel subassemblies. These research and developmental efforts contribute significantly to enhance the safety, economics, and efficiency of the KALIMER-600 design concept.

• Journal of Electrochemical Science and Technology
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• 제13권3호
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• pp.390-397
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• 2022

The use of microwaves as the energy source for synthesis and sintering of ceramics offers substantial advantages compared to conventional gas-fired and electric resistance furnaces. Benefits include much shorter processing times and reaching the sintering temperature more quickly, resulting in superior final product quality. Most oxide ceramics poorly interact with microwave irradiation at low temperatures; thus, a more complex setup including a susceptor is needed, which makes the whole process very complicated. This investigation pursued a new approach, which enabled us to use microwave irradiation directly in poorly coupled oxides. In many solid-state electrochemical devices, the support is either metal or can be reduced to metal. Metal powders in the support can act as an internal susceptor and heat the entire cell. Then sufficient interaction of microwave irradiation and ceramic material can occur as the sample temperature increases. This microwave heating and exothermic reaction of oxidation of the support can sinter the ceramic very efficiently without any external susceptor. In this study, yttria stabilized zirconia (YSZ) and a Ni-YSZ cermet support were used as an example. The cermet was used as the support, and a YSZ electrolyte was coated and sintered directly using microwave irradiation without the use of any susceptor. The results were compared to a similar cell prepared using a conventional electric furnace. The leakage test and full cell power measurement results revealed a fully leak-free electrolyte. Scanning electron microscopy and density measurements show that microwave sintered samples have lower open porosity in the electrode support than conventional heat treatment. This technique offers an efficient way to directly use microwave irradiation to sinter thin film ceramics without a susceptor.

• International Journal of Air-Conditioning and Refrigeration
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• 제11권2호
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• pp.51-60
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• 2003

In the nuclear power plant, emergency core coolant system (ECCS) is furnished at reactor coolant system (RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can occur due to coolant leaking in the check valve. The thermal stratification produces excessive thermal stresses at the pipe wall so as to yield thermal fatigue crack (TFC) accident. In the present study, effects of turbulence penetration on the thermal stratification into T-branches with square cross-section in the modeled ECCS are analysed numerically. Standard k-$\varepsilon$ model is employed to calculate the Reynolds stresses in momentum equations. Results show that the length and strength of thermal stratification are primarily affected by the leak flow rate of coolant and the Reynolds number of duct. Turbulence penetration into the T-branch of ECCS shows two counteracting effects on the thermal stratification. Heat transport by turbulence penetration from main duct to leaking flow region may enhance thermal stratification while the turbulent diffusion may weaken it.

• 대한의생명과학회지
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• 제14권4호
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• pp.239-242
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• 2008

Obesity results from a combination of genetic, environmental, and behavioral factors. Uncoupling proteins (UCP) are members of the larger family of mitochondrial anion carrier proteins (MACP). UCP separates oxidative phosphorylation from ATP synthesis with energy dissipated as heat, also referred to as the mitochondrial proton leak. UCP facilitates the transfer of anions from the inner to the outer mitochondrial membrane and the return transfer of protons from the outer to the inner mitochondrial membrane. Therefore, we investigated the genotype for the G>A polymorphism at the position -866 of UCP2 gene in Koreans and compared genotype of patients with control group. 50 patients (Male 22, Female 28), who previously underwent type 2 diabetcs (T2DM) and 30 controls (Male 14, Female 16) participated in this study. There was a weak significant association between -866 G>A polymorphism in UCP2 gene and T2DM. The present study shows that UCP2 -866 G>A polymorphism may not be associated with the pathogenesis of T2DM as opposed to the previous reports in other countries. Further studies with larger population may be needed for the development of diagnostic methods at genetic level such as DNA chip.

• Journal of Advanced Marine Engineering and Technology
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• 제32권3호
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• pp.379-386
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• 2008

The 36 liter LNG tank is designed to fit in the limited installation space of a small truck. Two LNG tanks allow one ton truck to run about 432 km per fueling. which is about 1.8 times longer than CNG mileage for the same truck. The variation of BOG with car acceleration for the different fuel liquid/vapor ratios in a tank is analysed by the modified Fortran program "Pro-Heatleak". Computational analyses show that the relationship between the BOG and liquid/vapor ratio is linearly proportional at a given acceleration. Fuel consumption decreases the volume of liquid fuel in the tank but increases the specific BOG. BOG increases with increasing of car acceleration when fuel liquid/vapor ratio is greater than 0.5 and decreases with increasing of car acceleration when fuel liquid/vapor ratio is less than 0.5. The difference between maximum and minimum BOG for full tank is about 12 percents. For the fuel liquid/vapor ratio equal to 0.5 BOG does not depend on car acceleration.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.116-116
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• 2010

진공 chamber에서 방전된 plasma 내부를 외부 view port를 통하여 확인하는 것은 극히 제한적이며 leak의 확률을 높이고 plasma의 균일한 방전을 방해한다. 이를 개선하기 위하여 내장형 무선 카메라를 chamber 내부에 위치한 후 고진공 영역에서 촬영을 시도하였으나 일반적인 CCD 카메라로는 촬영할 수 없다. 고진공 영역에서 카메라 내부온도의 급격한 상승이 원인으로 밝혀졌고 적정온도인 $45^{\circ}C$를 초과하여 최대 $96^{\circ}C$까지 4 min 이내에 상승함을 IR camera로 확인할 수 있었으며 이 때 카메라가 작동하지 않았다. 또한 카메라를 고진공 영역에서 촬영 및 녹화하기 위해서는 $46^{\circ}C$의 온도를 낮추어야 함을 진공해제 이후 내부온도가 $50^{\circ}C$로 감소하면서 내장형 무선 카메라가 다시 작동함으로 인해 알 수 있었다. 본 연구에서는 이를 해결하기 위하여 내장형 무선 카메라에 AM 변조 방식의 311 MHz RF remote controller를 장착하여 외부에서 선택적으로 ON/OFF 할 수 있도록 개조하였고 10 L chamber에서 150 L/sec TMP를 이용하여 10-6 Torr의 압력에서 성공적으로 녹화 및 촬영하였다. 또한 내장형 무선 카메라 내부의 반도체 회로 규격 및 발열량과 heat sink의 규격 (열전도도, 복사율)을 추가로 조사하였다. 분자유동 영역에서 열전달은 복사에 의한 영향이 대부분이므로 내장형 무선 카메라 내부 온도를 감소시켜 카메라의 작동 시간을 연장하기 위하여 내부 회로에 emissivity가 높고 전기전도도가 낮아 회로에 영향이 없는 박막을 회로에 증착시키는 추후의 연구가 필요하다.

• 설비공학논문집
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• 제15권3호
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• pp.239-245
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• 2003

In the nuclear power plant, emergency core coolant system (ECCS) is furnished at reactor coolant system (RCS) in order to cool down high temperature water in case of emergency. However, in this coolant system, thermal stratification phenomenon can occur due to coolant leaking in the check valve. The thermal stratification produces excessive thermal stresses at the pipe wall so as to yield thermal fatigue crack (TFC) accident. In the present study, effects of turbulence penetration on the thermal stratification into T-branches with square cross-section in the modeled ECCS are analysed numerically. $textsc{k}$-$\varepsilon$ model is employed to calculate the Reynolds stresses in momentum equations. Results show that the length and strength of thermal stratification are primarily affected by the leak flow rate of coolant and the Reynolds number of the main flow in the duct. Turbulence penetration into the T-branch of ECCS shows two counteracting effects on the thermal stratification. Heat transport by turbulence penetration from the main duct to leaking flow region may enhance thermal stratification while the turbulent diffusion may weaken it.