• Korean Chemical Engineering Research
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• 제56권1호
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• pp.49-55
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• 2018

에너지 위기 시대를 맞이하여 수소에너지가 가장 가능성 있는 대체에너지 중의 하나로 고려되고 있다. 액체수소는 기체수소와 비교하여 단위 부피당 에너지 밀도가 월등히 높으며 수소에너지의 탁월한 저장 방법으로 간주되고 있다. 본 연구에서는 2 상 모델에 기초를 둔 Navier-Stokes 식을 전산유체역학 프로그램을 이용하여 풀었으며, 초저온 냉각 튜브를 통과하면서 기체수소가 액화되는 과정을 분석하였다. 열전도율이 높은 구리관을 초저온 냉각을 위한 관의 재질로 가정하였다. 기체수소의 유입속도를 5 cm/s, 10 cm/s, 20 cm/s로 변화시키면서 냉각튜브 내 유체 온도분포, 축방향 및 반경방향 유체 속도, 기체 및 액체 수소 부피분율 분포를 각각 분석하였다. 본 연구 결과는 향후 액체수소 제조를 위한 기체수소 초저온 냉각기의 설계 및 제작을 위한 기초자료로 활용이 될 것으로 기대된다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.107-112
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• 2002

Ferritic stainless steels would be the most important alloys under the chloride environment. They are a cheaper alternative to austenitic stainless steels [1]. The present study is related to gas tungsten arc welding (GTAW) characteristics of Type 444 stainless steels. The heat of welding leads to grain coarsening in the HAZ and in the weld metal of ferritic stainless steels because they solidify directly from the liquid to the ferritc phase without any intermediate phase transformation. It is therefore recommended that these alloys be welded with a low heat input and at high welding speeds. Attempts to improve weldability were made by using of direct current straight polarity (DCSP) and pulsed current GTAW processes in this study. Measuring weld bead, grain size and Erichsen test were performed and the effects of heat input, pulse frequency on the weld metal and HAZ were studied. The main results were obtained as followings: decreasing heat input was effective to control the width of weld both in DCSP welding and in pulsed current welding; pulsed current welding was found to refine the grain size effectively and the finest grain size was found at the frequency of 150Hz in pulsed current welding; it was found that decreasing heat input also refine the HAZs effectively and the frequency had no different effect on HAZ at the same heat input; the ductility could be improved effectively in pulsed current welding.

• 한국항공우주학회지
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• 제38권4호
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• pp.363-368
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• 2010

고체추진제의 연소가 진행될 때, 고체상에서 액체상으로, 액체상에서 기체상으로의 상변화가 일어난다. 이 때 추진제 표면에서는 액체상, 기체상이 동시에 존재하게 된다. 액체상과 기체상의 중간에서는 액체상과 기체상의 혼합으로 인하여 거품이 형성되는데, 이 구간을 용융층(Melt Layer)이라고 한다. 용융층의 윗부분, 즉 액체상과 기체상 사이에는 연소면(Burning Surface)이 존재한다. 일반적으로 고체추진제가 연소될 때 생성되는 용융층의 두께는 1기압에서 약 1마이크론 정도이다. 본 연구에서는 물리적인 상변화 현상을 상방정식을 이용하여 액체에서 기체로의 상변화 현상을 모사하였다. 이를 통하여 연소면의 두께, 형성과 전파를 모사하였다.

• 한국안전학회지
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• 제27권6호
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• pp.59-63
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• 2012

The use of dry chemical powder has been increased as it can be stored for a long period and sustain in stable condition compared to gas or liquid phase extinguishing agents. A new type of dry chemical powder using Zeolite was produced in the research. Chemical powder was adsorbed into Zeolite 13X, a porous material appearing negative catalytic effect, to create extinguishing powder obtaining core shell structure and measured physical properties and run a small scale fire extinguishment. SEM, XRD, TA analysis was also executed, and extinguishing characteristics were measured by fire extinguishing experiment on oil pool fire. The experiment showed that the average particle size of Zeolite 13X was equivalent, indicating about $3{\pm}1{\mu}m$ and thermal analysis result illustrated that Zeolite 13X showed exothermic reaction peaks at $900^{\circ}C$ due to solid-state transformation. Extinguishing characteristics on oil fire of $NaHCO_3$/Zeolite 13X and $NH_4H_2PO_4$/Zeolite were improved, influenced by adsorbed extinguishing powders on Zeolite 13X and Zeolite 13X that contains high phase transition temperature.

• 한국주조공학회지
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• 제23권5호
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• pp.276-285
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• 2003

In the undercooled melt of $Pd_{40}Cu_{30}Ni_{10}P_{20}$ alloy, the solidification behavior including nucleation and growth of crystals at the micrometer level has been observed in-situ by use of a confocal scanning laser microscope combined with an infrared image furnace. The $Pd_{40}Cu_{30}Ni_{10}P_{20}$ alloy specimens were cooled from the liquid state to glass transition temperature. 575 K, at various cooling late under a helium gas flow. According to the cooling rate, the morphologies of the solidification front are changed among various types, irregular jog like front, columnar dendritic front, cellular grain, star like shape jog and fine grain, etc. The velocities of the solid-liquid interface are measured to be $10^{-5}{\sim}10^{-8}$ m/s which are at least two orders higher than the theoretical crystal growth rates. Combining the morphologies observed in terms of cooling rates and their solidification behaviors, we conclude that phase separation takes place in the undercooled molten $Pd_{40}Cu_{30}Ni_{10}P_{20}$ alloy. The continuous cooling transformation (CCT) diagram was constructed from solidification onset time at various linear cooling conditions with different rate. The CCT diagram suggests that the critical cooling rate for glassy solidification is about 1.5 K/s, which is in agreement with the previous calorimetric findings.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집 Vol.14 No.1
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• pp.562-564
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• 2001

Transformation of molecular film occurs only usually in air-water interface, 2 dimensions domain's growth and crash are achieved. Organic matter thin film that accumulate molecular film in archaism board only that consist of growth of domain can understand correct special quality of accumulation film supplying information about fine structure and properties of matter of device observing information and so on that is surface forward player and optic enemy using AFM one of SPM application by nano electronics. The stable images are probably due to a strong interaction between the monolayer film and glass substrate. We are unable to obtain molecule resolution in images of the films but did see a marked contrast between images of the bare substrate and those with the network structure film deposited onto it. Formation that prevent when gas phase state and liquid phase state measure but Could know organic matter that molecules form equal and stable film when molecules were not distributed evenly. and accumulated in solid state only.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 C
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• pp.1618-1620
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• 2002

Transformation of molecular film occurs only usually in air-water interface, 2 dimensions domain's growth and crash are achieved. Organic matter thin film that accumulate molecular film in archaism board only that consist of growth of domain can understand correct special quality of accumulation film supplying information about fine structure and properties of matter of device observing information and so on that is surface forward player and optic enemy using AFM one of SPM application by nano electronics. The stable images are probably due to a strong interaction between the monolayer film and glass substrate. We are unable to obtain molecule resolution in images of the films but did see a marked contrast between images of the bare substrate and those with the network structure film deposited onto it. Formation that prevent when gas phase state and liquid phase state measure but Could know organic matter that molecules form equal and stable film when molecules were not distributed evenly, and accumulated in solid state only.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집
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• pp.562-564
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• 2001

Transformation of molecular film occurs only usually in air-water interface, 2 dimensions domain's growth and crash are achieved. Organic matter thin film that accumulate molecular film in archaism board only that consist of growth of domain can understand correct special quality of accumulation film supplying information about fine structure and properties of matter of device observing information and so on that is surface forward player and optic enemy using AFM one of SPM application by nano electronics. The stable images are probably due to a strong interaction between the monolayer film and glass substrate. We are unable to obtain molecule resolution in images of the films but did see a marked contrast between images of the bare substrate and those with the network structure film deposited onto it. Formation that prevent when gas phase state and liquid phase state measure but Could know organic matter that molecules form equal and stable film when molecules were not distributed evenly, and accumulated in solid state only.