• 해양환경안전학회지
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• 제23권5호
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• pp.541-548
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• 2017

본 연구에서는 해양플랜트설비 건조 현장에서 사용되고 있는 기존 고온 오일 플러싱 장비에 대한 성능개선을 위해 기존의 플러싱 장치에 사용되던 오일에 질소가스를 혼합한 고온 오일 플러싱 시스템에 대하여 국제표준화기구 코드(ISO code)를 기준으로 이론적 연구를 수행하였다. 연구를 위해 오일-질소가스 혼합유체 플러싱 시스템 공정을 설계 후 청정성능에 영향을 주는 혼합유체의 혼합비율, 온도, 레이놀즈수 및 액상분율 등에 대한 공정모사 결과도 분석하였다. 그 결과 관 직경과 가스상의 체적분률이 일정한 상태에서 혼합유체의 체적유량이 증가될수록 수평 유압배관 입출구의 액상분율 차이 ${\Delta}{\alpha}_L$ 값은 증가하게 되고 배관길이 방향의 위치에 따라 오일과 질소가스 기포 사이의 상분포가 달라짐을 확인했다. 이러한 상분포의 변화는 오일-질소가스 혼합유체 플러싱 시스템의 청정성능에도 커다란 영향을 줄 것으로 예상된다.

• 공업화학
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• 제25권6호
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• pp.613-618
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• 2014

본 연구에서는 그래핀 옥사이드의 전기적 특성을 향상시키고자 그래핀 옥사이드에 암모니아수 처리를 이용하여 아민화가 이루어진 그래핀 옥사이드를 제조하였다. 그리고, 아민화된 그래핀 옥사이드의 전기적 특성을 평가하고자 이를 필름으로 제조하여 전자파차폐효율을 측정하였다. 암모니아수 처리 농도가 증가함에 따라 그래핀 옥사이드 표면의 질소 관능기가 증가함을 XPS에 의하여 확인하였으며, 또한, 전자파차폐효율 측정 결과 암모니아수 처리된 그래핀 옥사이드의 전자파차폐효율 특성이 우수함을 확인하였다. 21% 암모니아수 농도로 처리한 그래핀 옥사이드는 2950 MHz 이상에서 -5 dB 이상의 전자파차폐효율을 보여주었으며, 이러한 실험 결과들은 질소 관능기가 그래핀 옥사이드 내에 전자전달을 용이하게 하여 흡수되는 전자파 양을 증가시켰기 때문으로 사료된다.

• 한국물환경학회지
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• 제18권2호
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• pp.141-150
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• 2002

Two-stage membrane bioreactor using submerged hollow fiber membrane was applied in laboratory scale to treat nitrogen and phosphorus of domestic wastewater. Alum as the flocculant and adsorbent was added into the anaerobic basin of two-stage membrane bioreactor and mixed liquid of aerabic basin was recycled to the anaerobic basin for the purpose of nitrogen removal. Experiment was carried out to find removal efficient of phosphorous and nitrogen components in the mixed liquid, and the stability of the permeate flux and pressure of two-stage membrane bioreactor. In case of alum was added as the flocculant and adsorbent into the anaerobic basin, soluble phosphorus removal efficient was relatively higher and total permeate resistance(Rtot) was more increased out nitrogen removal efficient was lower as the result of lack of alkalinity and insufficient nitrification process than the case of alum was not added.

• 한국토양비료학회지
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• 제42권5호
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• pp.323-329
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• 2009

This study was conducted to analyze growth responses of fast growing tree species(8 clones of hybrid poplars, Salix alba, Metasequoia glyptostroboides, Liriodendron tulipifera, Acer okamotoanum, and Quercus palustris), the chemical characteristics of soil and $NO_3-N$ concentration of groundwater in a plantation applied with liquid pig manure. Concentrations of nitrogen and phosphorous in the soil treated with liquid pig manure were higher than that of the soil treated without liquid pig manure. With the exception of S. alba, DBH(Diameter at Breast Height) growth of all the fast growing tree species treated with liquid pig manure was higher than that of the species treated without liquid pig manure. In liquid pig manure treatment group, P. euramericana 'Eco28' clone showed the best performance in height and DBH growth. Concentration of nitrogen in the leaf with liquid pig manure was higher than that of the leaf treated without liquid pig manure. Based on the $NO_3-N$ concentration of groundwater analyzed during the experimental period, there was no evidence that groundwater was polluted by the liquid pig manure applied at the plantation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1359-1364
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• 2004

An experiment was performed to study the evaporation heat transfer and the pressure drop characteristics of liquid nitrogen in a horizontal stainless steel tube with wire coil inserts. The inner diameter of test tube is 4.3mm and the length is 1.5m. Four wire coils having different pitch and thickness were inserted into the plain test tube. The wire coil length is 1.5m and the diameter is 3.65mm with thickness of 0.5mm and 0.9mm. Experiments were conducted at saturation temperature of $-191^{\circ}C$ mass flux from 200 to 370 $kg/m^{2}s$ and heat flux of 62 $kW/m^{2}$. Direct heating method was used to apply heat to the test section. Boiling heat transfer coefficients of both the plain and the enhanced tubes were calculated. Pressure drops between inlet and outlet side of test section were also measured, and they are used to estimate EPR(Enhancement Performance Ratio).

• Progress in Superconductivity
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• 제11권1호
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• pp.52-56
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• 2009

Temperature distributions and thermal stresses were calculated and analyzed to investigate the effect of the artificial holes to the transient behaviors of the superconductors which was cooled in liquid nitrogen. Three dimensional finite element method was used to calculated the transient temperature and thermal stresses in the superconductors. The cooling speed of the superconductors with holes is faster than those without holes. Because the thermal stresses calculated in the superconductors can be relaxed by the distributed holes, the volume of the peak tensile stress decreases during the cooling in liquid nitrogen. If optimal metal, which can maintain the relaxation of thermal stresses, is used to fill and reinforce the artificial holes, the probability of failure of the superconductors may be decreased by the decrease of volume of peak tensile stress.

• 아시안잔디학회지
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• 제17권4호
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• pp.147-154
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• 2003

본 실험은 잔디에 아미노산 비료를 시비하였을 때, 잔디의 생육과 토양에 미치는 영향에 대해 조사하였다. 토양의 화학성을 비교한 결과 아미노산 액비 처리구에서의 토양 중 질소이용율이 대조구에 비해 70.6-90.1％ 증가하였다. 잔디식물체의 화학성을 비교한 결과 아미노산 액비 처리구에서 질소 함량, 고토 함량 및 엽록소함량이 대조구에 비해 각각 22-23％, 13％, 22-39％ 높아 잔디 건물중이 약 12％ 증가하여 잔디생육이 활발하였다. 본 실험을 통해 아미노산 액비를 시비할 경우 잔디의 토양 중 질소 이용율이 증가하여 잔디의 생육에 도움이 되고 있음을 알 수 있었다.

• Progress in Superconductivity
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• 제10권2호
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• pp.149-154
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• 2009

We measured and analyzed the quench development in coated conductor(CC) tapes. The CC was grown on hastelloy substrates and has an Ag protection layer. The tapes were subjected to simulated AC fault currents for quench development measurement. They were immersed in liquid nitrogen during the experiment. The quench resistance increased rapidly first, and the increase slowed down afterwards. It increased linearly with applied voltage at lower voltages, and depended less strongly on applied voltage at higher voltages. The resistance was compared with that of Au/YBCO films grown on sapphire substrates, and found to increase more monotonously than the latter. Data were analyzed quantitatively with the concept of heat transfer within the tape and the surrounding liquid nitrogen. A heat balance equation was derived and solved, taking into consideration temperature dependence of thermal parameters of the tapes. Solutions, together with values of thermal parameters taken from the literature, explained the data well. Cooling by liquid nitrogen affected the quench development considerably at lower applied voltages. Dependence on applied voltages could be also understood quantitatively.

• 한국초전도ㆍ저온공학회논문지
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• 제7권4호
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• pp.4-9
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• 2005

The degradation behavior of the critical current $(I_c)$ of Bi-2223 superconducting tapes under pressurized liquid nitrogen were investigated using a newly developed p-shaped sample holder which gives a series of bending strains to a sample. Three kinds of commercially available multi-filamentary Bi-2223 superconducting tapes were used. At atmospheric pressure, the Ie degradation behavior depended on the manufacturing process undergone by each tape. The tapes externally reinforced or densified by over pressure showed better bending strain tolerance than the Ag alloy-sheathed Bi-2223 tape. But these tapes showed a significant $I_c$ degradation when pressurized to 1 MPa in liquid nitrogen. For all samples, after depressurization to atmospheric pressure from 1 MPa, the Ie was completely recovered to its initial values at atmospheric pressure. When the samples were subjected to a thermal cycle wherein the tape was warmed up to room temperature after being depressurized from 1 MPa, it was found that the larger degradation of $I_c$ occurred at the regions where significant ballooning occurred, such as $0\%\;and\;0.2\%$. However, an improved ballooning damage tolerance was observed in the highly-densified tape.

• 한국초전도ㆍ저온공학회논문지
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• 제19권2호
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• pp.29-32
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• 2017

The use of electronic devices such as mobile phones and tablet PCs has increased of late. However, the power which is supplied through wires has a limitation of the free use of devices and portability. Magnetic-resonance wireless power transfer (WPT) can achieve increased transfer distance and efficiency compared to the existing electromagnetic inductive coupling. A superconducting coil can be applied to increase the efficiency and distance of magnetic-resonance WPT. As superconducting coils have lower resistance than copper coils, they can increase the quality factor (Q-factor) and can overcome the limitations of magnetic-resonance WPT. In this study, copper coils were made from ordinary copper under the same condition as the superconducting coils for a comparison experiment. Superconducting coils use liquid nitrogen to keep the critical temperature. As there is a difference of medium between liquid nitrogen and air, liquid nitrogen was also used in the normal conductor coil to compare the experiment with under the same condition. It was confirmed that superconducting coils have a lower reflection-coefficient($S_{11}$) than the normal conductor coils.