• Journal of the Korean Society of Safety
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• v.22 no.5
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• pp.77-83
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• 2007

This study is conducted on spontaneous ignition temperature and activation energy of Hydroxypropyl Methyl Cellulose(HMC) powder. HMC is a kind of cellulose derivative and used as additives for building material, surface coating, printing ink, adhesives, cosmetics and medical supplies. So this material has been widely used as important additive in the chemical industry fields and a mount of production has increased year by year. Therefore, it is very important to find out the thermal ignition characteristics of its danger and the critical ignition temperature. This study was performed by the Spontaneous Ignition Tester(SIT) and so on. Based on the data of the SIT-II, the critical ignition point of HMC is about $186^{\circ}C$ which is slightly lower than normal cellulose.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.2
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• pp.465-473
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• 2013

In this Study, the performance of precast PSC slabs with fire resistance panel for fire resistance of the tunnel system was evaluated by experimentally. The fire test was performed in fire resistance (electric) furnace according to RABT(Richtlinien fur die Ausstatung und den Betrieb von stra${\beta}$entunneln) time heating temperature curve. The test results showed that the measured temperatures at the t=0 mm depth of PSC slab with precast fire resistance panel during a fire was maximum temperature $367^{\circ}C$, lower than $380^{\circ}C$ (ITA 2004), when damage occurs. Also, at the t=25 mm, the maximum temperature was $239^{\circ}C$, which was lower than the damage temperature of rebar, $250^{\circ}C$. From the results, the use of precast fire resistance panel (t=25 mm) improves fire resistance of PSC structures.

• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.117-124
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• 2020

The present research focuses on a methodology to describe shearing response of clay with respect to temperature. An increase of temperature shifts the normal consolidation line to move down in the plane of void ratio and mean effective stress. The critical state line, however, does not move as much as the normal consolidation line in accordance with temperature increase. As temperature increase, therefore, the difference between the critical state mean effective stress and the pre-consolidation pressure reduces. To reflect this easily, the present study applies a bounding surface consisting of two parts divided by the critical state mean effective stress. This study calibrated a bounding surface for the soft Bangkok clay and performed elemental simulation for undrained triaxial compression tests. The elemental simulation showed that the model can describe the mechanical response upon temperature of clay without complex hardening and evolution rules compared to the experimental data.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.4
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• pp.16-25
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• 2004

Theoretical analysis for predicting the heat transport limitation of a copper powder sintered wick heat pipe was performed. The heat pipe diameter was 8mm and water was used for working fluid. The particle diameter was classified by 5 different meshes, and each capillary pressures and heat transport limitations. thermal resistances were analyzed according to the operating temperatures, wick thicknesses and inclination angles, based on the effective capillary radius($r_c$), porosity($\varepsilon$), Permeability (K). The wick capillary limitation was increased according as the particle diameter and the wick thickness and the operating temperature were increased. As the porosity and the capillary radius were larger. then the heat transport limitation was higher. The thermal resistance was greatly increased according as the wick thickness was increased.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.3
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• pp.33-41
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• 2016

Concrete is inherently a good fire-resistance material among all other constrcution materials and protects the reinforcing steel inside. This study investigates the material characteristics of concrete and steel bar inside the full scale reinforced concrete(RC) beam exposed to fire test. The fire test specimen was 4 m long and the test was conducted under no loading condition following KS F 2257. Fire source is simulated by ISO 834 and number of thermocouples were installed to measure temperature variation of surfaces and inside of the beam. The measured compressive strength of cored specimen, which was exposed to fire test, was 11 MPa, about 66% lower than the strength before exposure. The yielding strength of steel bar also decreased about 75 MPa, about 17% lower. The measured temperature of protected steel bar was around $649^{\circ}C$, the critical limit, after 4 hour exposure.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.94-94
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• 2017

지속적인 수질의 모니터링과 관리가 어려운 개발도상국의 경우, 모델링을 통한 병원균의 예측이 중요하다. Soil and Water Assessment Tool (SWAT)은 유역 모델로 병원균의 거동을 모의하는데 널리 활용된다. 하지만 SWAT이 모의하는 in-stream 모듈의 경우, 소멸, 부유, 퇴적의 단계만을 고려하여 정확도가 부족하다. 따라서 본 연구는 기존 모듈에 hyporheic exchange와 생장 단계를 추가하여 모듈의 성능 개선 및 열대 산지 유역에서의 병원균의 거동을 모의하였다. 본 연구는 몬순 기후 및 산지 지형을 가진 라오스의 Houay Pano 유역을 대상으로 대장균 (Escheichia coli, E.coli)의 거동을 2011년부터 2013년까지 일 단위로 모의하였다. 기존의 SWAT 박테리아 모듈의 경우, 소멸 단계만을 가지고 보정하였을 때 모델은 대부분 0의 값을 가졌고, 부유 및 퇴적 단계가 추가 된 후에는 우기시 대부분의 모델값이 관측값의 95% 신뢰 구간에 포함되었으나 건기에는 농도가 여전히 낮게 모의됨을 확인 할 수 있다. 건기 시 낮게 모의된 농도를 증가시키기 위해, 온도에 따른 생장 단계를 추가하였으며, 이때 생장 속도는 설정된 최소-최대 생장 온도 사이에서 최대값을 가진다. 하지만 온도에 따른 생장은 열대 기후의 특성상 전 기간에 걸쳐 동시에 증가하여 건기에만 낮게 모의된 농도를 보완하는 데는 한계가 있었다. Hyporheic exchange는 강바닥에 임시로 저장된 박테리아의 양이 특정 유량에 의해서 수계로 유입되는 현상으로, 본 연구에서는 일정한 양의 hyporheic flow를 가정하여 모의하였다. 결과적으로 Hyporheic exchange를 통해 유입되는 적은 양의 E.coli는 기존에 타당하게 모의된 우기의 농도는 그대로 유지하되, 건기에 낮게 모의된 농도는 증가시켜 기존 SWAT 모듈의 한계점을 잘 보완한 것을 확인 하였다. 결론적으로, 기존의 SWAT 모델은 건기 시 낮은 농도의 E.coli를 모의하기에 한계를 보였으며, 전 기간에 걸쳐 높은 온도를 유지하는 열대 기후에서 생장 단계는 이러한 한계를 보완하기에 적합하지 않은 것으로 판단되었다. 그러나 적은 양이 전 기간에 걸쳐 동일하게 유입되는 hyporheic exchange의 경우, 건기에 낮게 모의된 농도를 증가시켜 기존의 한계를 보완할 수 있었다.

• Korean Journal of Optics and Photonics
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• v.11 no.6
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• pp.379-384
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• 2000

We cooled cesium atoms below the Doppler cooling limit by laser cooling. For this deep cooling of atoms, the laser frequency was shifted by using the Zeeman shift of an absorption line of cesium. The stabilization of the laser frequency was maintained while the laser frequency was shifted by 40 MHz within 2 ms. The lowest temperature of the laser-cooled cesium atoms was $2.2\muK$\pm$0.5$\muK$in this experiment. We measured the temperature of the laser-cooled cesium atoms as a function of the frequency detuuing and the intensity of the cooling laser. The results agreed well with the ones calculated by two-photon laser cooling theory.theory.

• 기계와재료
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• v.22 no.3
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• pp.96-109
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• 2010

자동차는 다양한 형상과 기능을 가진 부품소재의 집합체라 할 수 있다. 자동차의 고출력화에 의한 연비향상과 각국의 환경규제 강화 요건을 충족시키기 위해 자동차 엔진의 작동온도와 이에 따른 배기가스의 온도가 꾸준히 높아지는 추세이다. 따라서 고온재료의 선택과 사용이 보다 중요해 지고 있다. 자동차에 사용되는 고온 부품은 설계사양에 맞추어 그리고 경제적인 측면을 고려하여 내열재료를 사용하는 방법과 표면처리를 하는 두 가지 방법이 주로 채택되고 있다. 내열재료를 사용하는 대표적인 부품은 엔진을 구성하는 부품과 연소실로부터 나오는 고온 고압의 배기가스가 이동하는 배기계 부품이다. 엔진을 구성하는 부품 중에는 냉각수에 의해 온도가 제어되는 부분은 경제적인 소재가 사용되나 밸브와 같은 부품은 고온재료가 채용된다. 가장 높은 온도에서 사용되는 배기계 부품에는 경제성이 감안되면서도 높은 열적, 기계적 안정성이 동시에 요구되고 있다. 전통적으로 배기부품에는 구상흑연주철이 널리 사용되어 왔고 현재에도 원가 측면의 강점을 이용해 대부분의 차량에 적용되고 있으나 일부 고출력, 고배기량 엔진의 경우에는 주철의 한계온도 이상의 배기온도가 요구되어 스테인리스 강을 도입하고 있다. 또한 내열 타이타늄 합금, 금속간화합물과 같은 고온재료가 개발됨에 따라 고가의 차종에는 신재료가 이들 부품으로 채용되고 있다. 이 글에서는 배기계 부품의 설계적인 요소에 의한 열적, 기계적 측면의 내구 특성을 살펴보고, 이들 부품에 보편적으로 적용되는 고온 금속재료의 종류 및 기계적 특성을 소개하였다. 아울러 미래의 환경친화적 자동차용 고온 부품을 개발하기 위하여 연구되고 있는 Super Si+MO, 스테인리스 강, TiAl, 고온 타이타늄 합금 등과 같은 자동차 내열 부품으로 사용되는 신소재의 연구개발 동향에 관하여 기술하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.12
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• pp.1829-1836
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• 2010

The district heating system distributes the heat generated from a cogeneration plant to wider locations. In this process, the district heating pipe (DHP) is subjected to internal and external loadings. The internal loadings are generally caused by the operating conditions such as water temperature and internal pressure. Frictional interactions between the pipes and the soil contribute to the external loadings. Thus, investigation of the mechanisms of failure of DHPs will help to guarantee both mechanical stability and heating efficiency. In this study, we investigate the local buckling of DHPs using limit state design (LSD). Two methods are considered: the use of the limit state for the width-thickness ratio and the use of the limit state for the strain. The results are used to confirm that the DHP is stable under local buckling. Finally, we suggest a minimum preheating temperature for avoiding local buckling.

• Korean Journal of Environmental Biology
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• v.38 no.2
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• pp.222-230
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• 2020

Temperature-dependent development models for Hydrochara affinis were built to estimate the ecological parameters as fundamental research for monitoring the impact of climate change on rice paddy ecosystems in South Korea. The models predicted the number of lifecycles of H. affinis using the daily mean temperature data collected from four regions (Cheorwon, Dangjin, Buan, Haenam) in different latitudes. The developmental rate of each life stage linearly increased as the temperature rose from 18℃ to 30℃. The goodness-of-fit did not significantly differ between the models of each life stage. Unlike the optimal temperature, the estimated thermal limits of development were considerably different among the models. The number of generations of H. affinis was predicted to be 3.6 in a high-latitude region (Cheorwon), while the models predicted this species to have 4.3 generations in other regions. The results of this study can be useful to provide essential information for estimating climate change effects on lifecycle variations of H. affinis and studies on biodiversity conservation in rice fields.