• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.1
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• pp.9-17
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• 2013

A considerable deal of work has been carried out to get an insight into the gas-solid suspension flows and to specify the particle motion and its influence on the gas flow field. In this paper an attempt is made to develop an analytical model to study the effect of nozzle inlet/exit pressure ratio, particle/gas loading and the particle diameter effect on gas-solid suspension flow. The effect of the particle/gas loading on the mass flow, Mach number, thrust coefficient and static pressure variation through the nozzle is analyzed. The results obtained show that the presence of particles seems to reduce the strength of the shock wave. It is also found that smaller the particle diameter is, bigger will be the velocity as bigger particle will have larger slip velocity. The suspension flow of smaller diameter particles has almost same trend as that of single phase flow with ideal gas as working fluid. Depending on the ambient pressure, the thrust coefficient is found to be higher for larger particle/gas loading or back pressure ratio.

• Journal of Korean Society of Forest Science
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• v.104 no.4
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• pp.527-535
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• 2015

With results from previous Korean studies on forest thinning, we conducted a meta-analysis on the effect of thinning on diameter at breast height (DBH) growth and carbon (C) stocks (tree, litter layer, coarse woody debris (CWD), and soils) in Korean forests. Thinning increased the DBH growth and the C stocks in soils by 39.2% and 12.8%, respectively, while it decreased the C stocks in tree by 30.9%. In contrast, thinning had no significant effect on the C stocks in litter layer and CWD. The DBH growth and the C stocks in tree showed significant correlations with thinning intensity and recovery time. The C stocks in litter layer correlated with recovery time while those in CWD and soils did not show significant correlation neither with thinning intensity nor with recovery time. Regression models of the DBH growth and the C stocks in tree were developed to quantify the effect of thinning intensity and recovery time. An integration of the regression model of the tree C stock into forest carbon models is expected to be essential to quantify the effect of thinning on the C stocks in litter layer, CWD, and soils. We also suggested expansion of study species, long-term and frequent monitoring, and investigation on understory vegetation in order to elucidate changes in Korean forests following thinning practices.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.1
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• pp.25-36
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• 2021

Hydrogen in hydrogen-electric vehicles has a wide range of combustion and explosion ranges, and is a combustible gas with a very fast flame propagation speed, so it has the risk of leakage, diffusion, ignition, and explosion. The fuel tank has a Thermally active Pressure Relief Device (TPRD) to reduce the risk of explosion and other explosions, and in the event of an accident, hydrogen inside the tank is released outside before an explosion or fire occurs. However, if an accident occurs in a semi-closed space such as an underground parking lot, the flow of air flow is smaller than the open space, which can cause the concentration of hydrogen gas emitted from the TPRD to accumulate above the explosion limit. Therefore, in this study, the leakage rate and concentration of hydrogen over time were analyzed according to the diameter of the nozzle of the TPRD. The diameter of the nozzle was considered to be 1 mm, 2.5 mm and 5 mm, and ccording to the diameter of the nozzle, the concentration of hydrogen in the underground parking lot increases in a faster time with the diameter of the nozzle, and the maximum value is also analyzed to be larger with the diameter of the nozzle. In underground parking lots where air currents are stagnant, hydrogen concentrations above LFL (Lowe Flammability Limit) were analyzed to be distributed around the nozzle, and it was analyzed that they did not exceed UFL (Upper Flammability Limit).

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.12-12
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• 2010

첨단 공정이 필요한 반도체와 LCD, PDP, LED 등의 디스플레이 및 IT 부품을 제조하는데 필요한 장비의 고성능화와 작업환경의 고청정화에 따른 초고진공펌프의 수요 확대와 앞으로 전개될 한-미 FTA에 따른 시장 확대로 인해 크라이오펌프의 국산화가 시급한 실정이다. 고성능 크라이오펌프를 만들기 위해서는 냉각판을 극저온으로 냉각하기 위한 극저온 냉동기 개발도 중요하지만 냉각판(cryoarray)에 최대한 많은 분자를 포획시키는 것 또한 최우선적으로 고려되어야 할 사항 중 하나이다. 이에 본 논문은 크라이오펌프용 냉각판의 분자포획능력에 대하여 연구하였다. 해석에 이용한 냉각판은 현재 상용화된 모델들 중 원형 중앙판에 $45^{\circ}$ 하향 skirt가 달린 형태이며 8장의 냉각판이 일정한 간격을 두고 아래쪽으로 적층되어 있다. 냉각판의 분자포획능력의 해석은 형상계 수법(view factor method)을 이용해 수행하였다. 형상계수법은 크라이오펌프를 n개의 미소면적으로 구성된 밀폐된 공간으로 가정하고 각 미소면적요소의 온도와 흡착계수, 표면조건 그리고 분자유속이 일정하다는 조건을 이용해 분자유속에 관해 n개의 대수연립방정식을 얻고 이 대수연립방정식을 풀어 냉각판의 분자포획능력을 구한다. 해석에 이용한 냉각판의 기체분자포획능력이 구속된 형상에서 얼마나 우수한 가를 알아보기 위해 중앙판의 직경, 입구와 냉각판 사이의 거리, 그리고 각 냉각판 사이의 거리를 변화시켜가며 해석을 수행하고 그 결과를 비교, 분석하였다.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
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• 2007.10a
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• pp.221-225
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• 2007

산림은 탄소저장능력이 있어 대표적인 온실가스인 이산화탄소를 저감시킨다. 따라서 산림의 탄소저장능력 특성을 규명하고 그것을 산림경영에 반영함으로써 온실가스 저감이라는 국제적 노력에 동참하는 수단으로 활용할 수 있다. 일반적으로 임분에서의 탄소저장능력(Carbon Storage, CS)은 식생탄소저장능력(Vegetation Carbon Storage, VCS)과 토양탄소저장능력(Soil Carbon Storage, SCS)의 합으로 볼 수 있다. 본 연구에서는 우리나라 대표적인 자생수종인 소나무림 VCS의 공간분포를 지엽적 범위(spot level)에서 광역적 범위(regional level)로 확대하여 그 특성을 규명하는 방법을 제시하고자 한다. 지엽적 범위의 조사 및 연구에서 VCS는 임목의 흉고직경(Diameter at Breast Height)과 밀접한 관계가 있는 것으로 확인되었다. 이러한 관계와 Quickbird 고해상도 위성영상에서 추출한 소나무림 공간분포도를 이용해 경관범위(landscape level)에서 소나무림 탄소저장능력의 공간분포를 추정할 수 있었으며,그 결과를GIS 및 RS를 통해 광역적 범위로 확대하였다.

• Journal of the Korea Institute of Building Construction
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• v.18 no.2
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• pp.99-107
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• 2018

The objective of the present study is to propose a reliable shape of supplementary V-ties in the section jacketing approach for seismic strengthening of reinforced concrete columns. A total of 24 pull-out specimens were prepared. The test parameters selected with regard to bond strength of V-ties were the shape of V-ties, embedment length of V-tie legs, and compressive strength of concrete. The measured bond strength of V-ties with different shapes were compared with that of the conventional V-ties and predictions using CEB-FIP equation. Ultimately, V-ties with pressed end-details at their legs could be recommended for the supplementary lateral reinforcement of strengthening columns with jacketing thickness less than the embedment length [= max (75mm, $6d_b$)] of conventional V-ties, where $d_b$ is the diameter of the reinforcing bar used for V-ties.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.8
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• pp.807-812
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• 2005

This study is to investigate the correlation of pore structures of Zeolite 5As modified with acid and their adsorption capacity of toluene vapor using the dynamic adsorption method. The experimental results showed that the modification with acid allowed more micropores and enlarged the existing pores. Toluene vapor was mainly adsorbed on the surface of pores over $15\;{\AA}$ in diameter. The equilibrium adsorption capacity of toluene vapor of the modified Zeolite 5As was in the range of $15{\sim}70\;mg/g$ and the equilibrium adsorption capacity was increased to f times than that of the Zeolite 5A. The correlation between the total cumulative surface area and the equilibrium adsorption capacity was hard to say linear. The correlation in diameter between the cumulative surface area in the range of over $15\;{\AA}$ and the equilibrium adsorption capacity gate the highest correlation factor of 0.997.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1998.05a
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• pp.13-18
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• 1998

vortex tube는 간단한 구조의 관을 이용하여 어떠한 화학작용이나 연소작용 없이 압축유체를 저온 및 고온부분으로 분리하는 에너지 분리장치이다. 금속학자 Georges Joseph Ranque에 의해 vortex tube의 에너지분리 현상이 발견된 후 vortex tube는 공작기계에 의한 금속가공에 있어서 가공물의 열변형을 막기 위한 국소냉각, 금형제품의 급속냉각 또는 냉각복(air cooling jacket)에 사용하거나 공기공급식 호흡보호구의 공기공급시스템에 많이 활용되고 있다. vortex tube를 이용한 냉각복 및 호흡보호구는 소형, 경량으로서 근로자의 직접적인 조작이 간단하고, 열기가 신체에 직접적으로 닿지 않아 안전하고, 냉각효율이 높을 뿐만 아니라 매우 경제적이어서 그 이용률이 점차 확대될 전망이다. (중략)

• Proceedings of the Korean Society for Bio-Environment Control Conference
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• 1995.10a
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• pp.100-102
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• 1995

국내 양액재배 면적은 94년말 53.5ha로 90년의 8.1ha에 비해 급격히 확대되었으며, 이중 오이는 15.5ha로 36%를 점유하고 있다. 오이의 경우 펄라이트경이 58.4%로 고형배지경이 대부분을 차지하고 있는데 이는 근권환경의 안정성이 높아 재배의 위험성을 경감시킬 수 있기 때문으로 생각된다. 그러나 펄라이트의 경우 자체가 갖는 수분보유력은 크지만 입자 직경에 따라 배수성이 지나치게 커서 정식후 초기활착이 곤란해질 우려가 있으므로 금액방법의 적정화, 입자크기의 선택, 왕겨, 훈탄, 입상암면 등 다양한 이종배지를 이용한 혼합배지의 활용 등을 검토할 필요가 있는 것으로 알려지고 있다. (중략)

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.1063-1067
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• 1997

A study of carbide step drill cutting ability is highly progessing the step drill with more then twice diameter rate is so difficult in regrinding and very easy to damage during machining. As the machining of step drill for closed hole is occur to breakage at small diamter poistion, so it is very difficult to machinine. Thue, in this experiment, We investance roundness and surface roghness by machining distance and were identifid that the first distance, 5~10m, was fine with 7 .mu.m but the arround of 15m was happened so much alternation. And we were indentified that after 20m was happend statable machining. The surface roughness was happened the same conditions. So application of stwp drill we think that the selection of cutting conditions need lots consideration and the study of step drill's diameter ratio ratio is carred out.