• 품질경영학회지
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• 제48권1호
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• pp.51-68
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• 2020

Purpose: The primary objective of this research is to develop the optimal operating conditions as well as their associated design spaces for a Cryogenic Submerged Arc Welding(SAW) process by improving its quality and productivity simultaneously. Methods: In order to investigate functional relationships among quality characteristics and their associated control factors of an SAW process, a stepwise design of experiment(DoE) method is proposed in this paper. Based on the DoE results, not only a multi-dimensional design space but also a safe operating space and normal acceptable range(NAR) by integrating statistical confidence intervals were demonstrated. In addition, the optimal operating conditions within the proposed NAR can be obtained by a robust optimal design method. Results: This study provides a customized stepwise DoE method (i.e., a sequential set of DoE such as a factorial design and a central composite design) for Cryogenic SAW process and its statistical analysis results. DoE results can then provide both the main and interaction effects of input control factors and the functional relationships between the input factors and their associated output responses. Maximizing both the product quality with high impact strength and the productivity with minimum processing times simultaneously in a case study, we proposed a design space which can provide both acceptable productivity and quality levels and NARs of input control factors. In order to confirm the optimal factor settings and the proposed NARs, validation experiments were performed. Conclusion: This research may provide significant contributions and applications to many SAW problems by preparing a standardization of the functional relationship between the input factors and their associated output response. Moreover, the proposed design space based on DoE and NAR methods can simultaneously consider a number of quality characteristics including tradeoff between productivity and quality levels.

• 한국결정성장학회지
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• 제23권2호
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• pp.108-113
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• 2013

$CuInSe_2$(CIS) chalcopyrite 물질은 고효율 박막 태양전지를 위한 광흡수층의 물질로 매우 잘 알려져 있다. 최근 태양광 산업의 흐름은 안정적인 재료 개발과 가격 경쟁력 있는 태양전지를 위한 효율적인 제조 공정을 일치시키는 것이다. 저가의 CIS 광흡수층 위해 다양한 방법으로 제조를 시도하였고, 본 논문에서는 CIS 광흡수층을 저가형으로 제조를 위해 상용화되는 6 mm pieces를 사용하여 high frequency ball milling과 cryogenic milling을 이용해 CIS 나노입자를 얻었다. 그리고, CIS 광흡수층은 불활성 분위기의 glove box 안에서 milling된 나노입자를 사용하여 paste coating법으로 제조하였다. Chalcopyrite CIS 박막은 기판온도 550도에서 30분간 셀렌화 한 후 성공적으로 제조되었으며, Al/ZnO/CdS/CIS/Mo 구조의 CIS 태양전지는 evaporation, sputtering 및 chemical bath deposition(CBD) 등 다양한 증착 방법으로 각각 제조하였다. 결론적으로, 나노입자를 이용한 CIS 태양전지 전기적 변환효율은 1.74 %를 얻었으며, 개방전압(Voc)는 29 mV, 합선전류밀도(Jsc)는 35 $mA/cm^2$, 그리고 충진율(FF)은 17.2 %였다. 나노입자 CIS 광흡수층은 energy dispersive spectroscopy(EDS), x-ray diffraction(XRD) 그리고 high-resolution scanning electron microscopy(HRSEM) 등으로 특성 분석을 하였다.

• 동력기계공학회지
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• 제14권2호
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• pp.28-33
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• 2010

In this research, cascade liquefaction process was simulated using two-staged direct expansion with inter-cooler. Evaporated gaseous refrigerant which has low pressure and temperature from the inter-cooler is mixed with gaseous refrigerant from outlet of 1st compressor, and flows into 2nd compressor. Therefore this prevents superheating compression. Compressor work of process which includes inter-cooler to all cycles shows the lowest value of 338.68 MW and it is lower 16.34% than that of basic process. Refrigeration capacity shows decreasing tendency as applied inter-cooler and that of process which includes inter-cooler to all cycles shows the lowest value of 449 MW. COP was increased when the inter-cooler was applied, and process which includes inter-cooler to all cycles shows highest value of 1.33. It shows that COP was increased because decrement of compressor work by applying inter-cooler was higher than decrement of refrigeration capacity.

• 한국기계가공학회지
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• 제11권3호
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• pp.160-165
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• 2012

The packing, among the components comprising the gate valve, is used to sustain the air-tightness and the study on change of shape or pattern has been carried out to maximize the functions, but the study on changing the location or the size of the packing in a bid to prevent the freezing has rarely been implemented. Thus, This study is intended to evaluate the thermal strain of packing by heat transfer from territory of extremely low temperature as well as the temperature distribution to the upper part of the packing using numerical analysis method.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.676-677
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• 2010

나로우주센터에서 2차에 걸친 나로호 발사가 수행되었다. 나로호 발사를 위한 나로우주센터 발사대는 연료 및 산화제, 고압가스 등 발사체 발사운용에 필요한 추진제 공급설비를 갖추고 있으며, 본 논문에서는 발사대 추진제 공급설비 중 극저온 추진제인 액체산소 충전시스템에 대한 개발 과정 및 운용방법에 대해 고찰한다.

• 한국초전도ㆍ저온공학회논문지
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• 제19권1호
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• pp.13-16
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• 2017

Water issue, especially water pollution, is a serious issue of 21st century. Being an significant technique for securing water resources, superconducting magnetic separation wastewater system was indispensable. A large bore conduction-cooled magnet was custom-tailored for wastewater treatment. The superconducting magnet has been designed, fabricated and tested. The superconducting magnet was composed of NbTi solenoid coils with an effective horizontal warm bore of 400 mm and a maximum central field of 2.56T. The superconducting magnet system was cooled by a two-stage 1.5W 4K GM cryocooler. The NbTi solenoid coils were wound around an aluminum former that is thermally connected to the second stage cold head of the cryocooler through a conductive copper link. The temperature distribution along the conductive link was measured during the cool-down process as well as at steady state. The magnet was cooled down to 4.8K in approximately 65 hours. The test of the magnetic field and quench analysis has been performed to verify the safe operation for the magnet system. Experimental results show that the superconducting magnet reached the designed magnetic performance.

• 한국초전도ㆍ저온공학회논문지
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• 제22권3호
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• pp.20-24
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• 2020

The purpose of this analytic study is to design and examine an efficient hydrogen liquefaction cycle by using a pre-cooler. The liquefaction cycle is primarily comprised of a pre-cooler and a refrigerator. The fed hydrogen gas is cooled down from ambient temperature (300 K) to the pre-cooling coolant temperature (either 77 K or 120 K approximately) through the pre-cooler. There are two pre-cooling methods: a single pre-coolant pre-cooler and a cascade pre-cooler which uses two levels of pre-coolants. After heat exchanging with the pre-cooler, the hydrogen gas is further cooled and finally liquefied through the refrigerator. The working fluids of the potential pre-cooling cycle are selected as liquid nitrogen and liquefied natural gas. A commercial software Aspen HYSYS is utilized to perform the numerical simulation of the proposed liquefaction cycle. Efficiency is compared with respect to the various conditions of the heat exchanging part of the pre-cooler. The analysis results show that the cascade method is more efficient, and the heat exchanging part of the pre-coolers should have specific UA ratios to maximize both spatial and energy efficiencies. This paper presents the quantitative performance of the pre-cooler in the hydrogen liquefaction cycle in detail, which shall be useful for designing an energy-efficient liquefaction system.

• 한국가스학회지
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• 제1권1호
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• pp.41-48
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• 1997

가스물성의 계산방법으로 상태방정식이 널리 사용되고 있으나 상태방정식의 종류에 따라서 물성예측에 서로 다른 차이를 보이고 있다. 본 연구는 가스의 액화온도에서 상온에 이르는 온도범위와 1bar에서 30bar에 이르는 압력범위에서 질소, 산소, 아르곤에 대한 상태방정식의 물성계산 신뢰도를 검토하고자 하였다. 이를 위하여 Aspen plus에서 제공하는 Soave-Redlich-Kwong, Peng-Robinson, BWR-Lee Staring 상태방정식을 비교대상으로 하였고 계산결과는 문헌치 및 virial식과 비교하였다. 또한 물성계산식이 공정에 미치는 영향을 고찰하기 위하여 초저온 공기분리장치의 증류탑 및 팽창터어빈 계산을 수행하여 상태방정식 차이에 의한 공정계산 차이를 비교, 분석하였다.

• 한국재료학회지
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• 제34권1호
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• pp.44-54
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• 2024

High-Manganese (Mn) austenitic steel, with over 24 wt% Mn content, offers outstanding mechanical properties in cryogenic settings, making it a potential replacement for existing cryogenic materials. This high manganese steel exhibits high strength, ductility, and wear resistance, making it promising for applications like LNG tanks, flanges, and valves. To operate in cryogenic environments, hot forging and heat treatment processes are vital, especially in flange production. The cooling rate during high-temperature cooling after hot forging plays a critical role in influencing the microstructure and mechanical properties of high manganese steel. The rate at which cooling occurs during this process influences the size of the grains and the distribution of manganese and consequently has an impact on mechanical properties. This study assessed the microstructure and mechanical properties based on different cooling rates during the hot forging of High-Mn steel flanges. Comparing air and water cooling after hot forging, followed by heat treatment, revealed notable differences in grain size. These differences directly impacted mechanical properties such as tensile strength, hardness, and Charpy impact property. Understanding these effects is crucial for optimizing the performance and reliability of High-Mn steel in cryogenic applications.

• 한국수소및신에너지학회논문집
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• 제35권1호
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• pp.34-39
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• 2024

Korea government is trying to supply liquid hydrogen from another country to domestic The research for liquid hydrogen transportation and liquefaction plant of hydrogen underway for several years, and empirical research is also planned in the future. Along with the development of liquid hydrogen transport ship/liquefaction plant technology, the development of liquid hydrogen reception base technology must be carried out. In this study, a concept level liquid hydrogen receiving terminal is constructed based on the process of the LNG receiving terminal. Based on this, a study is conducted on the development of analysis technology for the amount of BOG (pipe, tank) generated during cooldown and unloading in the liquid hydrogen unloading line (loading arm to storage tank). The research results are intended to be used as basic data for the design and liquid hydrogen receiving terminal in the future.