• Journal of the Korean Institute of Gas
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• v.17 no.1
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• pp.26-34
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• 2013

The multiphase flow analysis related to phase change can be adapted to lots of areas such as evaporation and condensation has many interesting branches due to complicated phenomenon. In this study, the experimental investigation of cryogenic liquid in the porous media with various densities was shown how the cryogenic liquid behaves in the porous structure. For this study, permeability behaviors under different applying pressure of the glass wool with different bulk densities are discussed. Experimental investigation on the behavior of cryogenic liquefied nitrogen in the porous media is conducted. The result was that the non linearity of pressure gradient with location is increased and the permeability is decreased as the bulk density of glass wool increased. Lastly, simulation results with CFD commercial package program are used to realize the cryogenic liquid's flow in porous media to compare the finding with experimental results.

• Journal of the Korean Institute of Gas
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• v.19 no.6
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• pp.28-33
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• 2015

In this study, a dual fuel engine fueled with natural gas and diesel was tested to investigate the effects of heating value variation of CNG fuel. CNG substitution rate which is defined as the ratio of CNG and diesel supplied in a heating value basis was fixed at 80%. The higher heating value was varied from $10,400kcal/Nm^3$ to $9,400kcal/Nm^3$ by mixing nitrogen gas with pure CNG and diesel fuel was injected at a fixed injection timing. The engine test results showed that thermal efficiency and power output were decreased as the heating value of mixed CNG fuel was decreased. And the peak cylinder pressure was also decreased but the ignition delay time and the combustion duration and timing were almost same.

• Journal of Korean Society of Forest Science
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• v.107 no.2
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• pp.140-150
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• 2018

For the estimation of greenhouse gas dynamics in forests, it is useful to use a model which simulates both carbon (C) and nitrogen (N) cycle simultaneously. A forest C model, called FBDC, was developed and validated in Korea. However, studies on development of forest N model are insufficient. This study aimed to suggest a development process of a forest C and N model. We analyzed the general features, structures, ecological processes, input data, output data, and methods of integrating C and N cycles of the VISIT, Biome-BGC, Forest-DNDC, and O-CN. The structure and features of the FBDC were also analyzed. The VISIT was developed by integrating forest C model with a N cycle module, and the new model also could be designed by combining the FBDC with a N cycle module. The VISIT and Forest-DNDC could estimate soil $N_2O$ emissions, and the integrated model should include the processes shared by these models. Especially, the overseas models linked C and N cycles based on N absorption, C absorption, and decomposition of dead organic matter. Therefore, the integration of the FBDC with N cycle module should apply this linkage of structures between C and N cycles. Climate, soil texture, and species distribution data, which are essential for the model development, were available in Korea. However, parameter data associated with N cycle and validation data for soil $N_2O$ emissions need to be obtained by field studies.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.5
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• pp.516-520
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• 1999

Mechanical alloying (MA) by planetary type ball mill of pure iron powders was carried out under the ammonia gas atmosphere. The powders of metastable iron nitrides was synthesized up to the nitrogen content of 23 at% N. The observed phases are identified as the super-saturated bcc solid solution for the nitrogen concentration below 14.5 at% N and the non-equilibrium hcp phase stable at high temperature for 20.8 at.% N. Magnetization of Fe-N powders gradually decreases with increasing the N concentration on contrast to the enhancement reported for the bct iron nitrides. Neutron diffraction experiments also provide detailed information concerning the local atomic structure surrounding the nitrogen atoms. The coordination number of Fe atom around a nitrogen atom for the iron nitride containing 9.5 at% N turns out to be 3.9 atoms. This suggests that a nitrogen atom is situated at a center of the tetrahedron formed by iron atoms.

• Journal of the Korean Institute of Gas
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• v.10 no.3 s.32
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• pp.60-64
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• 2006

Explosion range and explosion characteristics of by product gas from carbon black manufacturing process were studied. About 75% of the by product gas were composed with water vapour and nitrogen. And the combustible component in the gas were hydrogen, methane, acetylene and carbon mono-oxide. Because of the combustible components in the by product gas there are explosion hazards in the gas handling process. Explosion range of the gas by experiment was from 17.1% to 70.7% and the value has considerable difference with the calculated value from Lechatelier law. Explosion pressure of the gas was $5.4kg/cm^2$ and the average explosion pressure rise rate was $39.2kg/cm^2/s$. Based on the experimental result we can expect that a explosion or fire accident during the handling the gas can make a severe loss, therefore there should be a explosion prevention or protection measures in the gas handling process.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.11
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• pp.749-757
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• 2017

To cope with the development of alternative fuels and international environmental regulations, this study provides a numerical analysis of the effects of composition and temperature changes of n-decane and ethanol on auto-ignition characteristics. CHEMKIN-PRO is used as the analysis program and the LLNL model is used as the reaction model. The numerical results show that the ignition delay time increases as the mole fraction of ethanol increases for temperatures below 1000 K, where low temperature reactions occur. Because of the high octane number of ethanol, the high percentage of ethanol delays the increase in the concentration of OH radicals that cause ignition. The oxygen concentration in the mixture is changed to apply the exhaust gas recirculation and a numerical analysis is then performed. As the oxygen concentration decreases, the total ignition delay time increases because the nitrogen gas acts as a thermal load in the combustion chamber.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.179-179
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• 2016

희토류계 영구자석은 높은 보자력과 잔류 자화을 가지고 있어 자기기록저장매체, MEMS(엑츄에이터), 센서 등의 응용 분야에 적용시키기 위해 다양한 연구들이 진행되고 있다. 하지만 희토류계 원소의 수급 및 가격의 문제점으로 친환경자석으로의 전환 및 희토류나 중희토류를 사용하지 않는 비희토류계 영구자석을 개발하는 연구에 대한 필요성이 대두되고 있다. 이 중 Fe-N 계 자성 물질인 $Fe_{16}N_2$는 포화 자화 값이 현재까지의 자성물질 중 가장 높은 값(240emu/g)을 나타내며 상대적으로 높은 결정자기이방성 상수를 가지고 있어 비희토류계 영구자석 물질 중 하나로 주목받고 있다. 본 연구에서는 $Fe_{16}N_2$ 박막을 얻기 위해 DC Magnetron Sputtering 방법을 이용하여 Si wafer 위에 박막을 증착하고 증착공정 조건 중 질소 유량 및 Sputtering Power를 변수로 따른 박막의 성장, 조직변화, 자성 특성을 관찰을 통해 최적의 공정 조건을 찾고자 하였다. $N_2$ 가스 유량 변화에 따른 박막의 성장 속도는 거의 변화가 없었으며 $N_2$ 가스 유량의 증가에 따라 박막 내 Fe의 함유량은 감소하였다. 모든 공정 조건에서 $Fe_3N$, $Fe_4N$, $Fe_{16}N_2$ 상들이 섞여 성장하였으며 XRD를 통한 상분석과 더불어 VSM을 통한 자성 특성을 분석해본 결과 $Fe_{16}N_2$의 분율이 가장 높게 성장된 공정 조건은 Power는 200W, $N_2$ 가스 유량은 20sccm이었으며 이 조건에서 2.45T의 포화 자화 값과 1.4T의 잔류 자화 값을 얻을 수 있었다.

• Journal of the Korean Vacuum Society
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• v.18 no.3
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• pp.164-175
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• 2009

CFD is used to analyze gas flow characteristics, power absorption, electron temperature, electron density and chemical species profile of an internal antenna type inductively coupled plasma system. An optimized grid generation technology is used for a complex real-scale models for industry. A bare metal antenna shows concentrated power absorption around rf a feeding line. Skin depth of power absorption for a system is modeled to 50 mm, which is reported 53 mm by experiments. For an application of bipolar plates for hydrogen fuel cells, multi-sheet loading ICP nitriding system is proposed using an internal ICP antenna. It shows higher atomic nitrogen density than reported simple pulsed dc nitriding systems. Minimum gap between sheets for uniform nitriding is modeled to be 39 mm.

• Journal of the Korean Vacuum Society
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• v.16 no.2
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• pp.122-127
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• 2007

In this research, amophous carbon films (a-C, a-C:H, a-C:N) were synthesized by closed-field unbalanced magnetron (CFUBM) sputtering using graphite target. We also fabricated amorphous carbon films with applying negative DC bias voltage of 200 V in during the deposition in working pressure. Also, a-C:H and a-C:N films was synthesized by adding acethylene($C_{2}H_{2}$) and nitrogen(N) gases of 4 and 3 sccm into Ar pressure. The a-C:H film synthesized at -200 V exhibited the maxumum hardness of 26.3 GPa, the smooth surface of 0.1 nm and the good adhesion of 30.5 N. And a-C:N film synthesized at -200 V exhibited at -200 V exhibited the best adhesion of 32 N. This paper examined the effect of $C_{2}H_{2}$ gas, $N_{2}$ gas and negative DC bias voltage as the parameter for improving the physical properties and the relation between structral and physical properties of carbon films.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2010.04a
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• pp.192-192
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• 2010

현재 산업과 과학의 발달로 인한 무분별한 화석연료의 사용은 에너지자원의 고갈과 환경오염의 문제를 야기시켜, 이의 해결을 위한 청정 신에너지에 대한 연구가 전 세계적으로 집중되고 있다. 이 중 바이오매스는 화석연료보다 비교적 높은 H/C 비를 갖기 때문에 신에너지인 수소 또는 Syngas를 생산하기 위한 가스화 특성이 우수한 특징을 가지고 있으며, 구성성분 내 중금속, 황, 질소를 거의 함유하지 않는 점에서 환경오염 저감과 동시에 대체 신에너지로써 각광을 받고 있다. 이에 본 연구에서는 목질계 바이오매스인 Wood pellet (미송)에 대하여 고정층 반응기를 이용하여 질소분위기하에서 온도 및 Steam/Biomass Ratio(이하 SBR) 조건에 따른 가스화 특성으로 고찰하는데 그 목적을 둔다. 온도의 영향에 대하여, 높은 온도 범위에서 수소 수율이 증가함을 알 수 있었다. SBR에 대한 영향으로서, 저온 (700, $800^{\circ}C$)에서는 SBR=1에서는 수소의 수율이 증가하였으나 SBR=2, 3에서 감소하는 것을 보였다. 하지만 $900^{\circ}C$에서는 SBR이 증가 할수록 수소의 수율이 증가하는 것으로 나타났다. 또한 볼륨비로 나타내었을 경우 $H_2/CO(vol/vol)$의 경우 $900^{\circ}C$, SBR=3에서 0.73%로 water gas shift reaction이 가장 잘 일어난 것을 확인했고, $H_2/CH_4(vol/vol)$의 경우 마찬가지로 위의 조건과 동일조건에서 2.59%로 steam reforming이 가장 잘 일어난 것을 확인할 수 있었다. 최종적으로 본 실험에서는 $900^{\circ}C$, SBR=3인 경우에 가장 높은 수소수율을 얻을 수 있으며, 이때 수소의 수율은 32.7 Vol%였다.