• 한국주조공학회지
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• 제42권1호
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• pp.61-66
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• 2022

Hydraulic units are important components of agricultural and construction machinery, and thus require high-quality castings. However, gas defects occurring inside the sand cores of the castings due to the resin used is a problem. This study therefore aimed to develop a casting simulation method that can clarify the gas defect positions. Gas defects are thought to be caused by gas generated after the molten metal fills up the mold cavity. The gas constant is the most effective factor for simulating this gas generated from sand cores. It is calculated by gas generating temperature and analysis of composition in the inert gas atmosphere modified according to the mold filling conditions of molten metal. It is assumed that gases generated from the inside of castings remain if the following formula is established. [Time of occurrence of gas generation] + [Time of occurrence of gas floating] > [Time of occurrence of casting surface solidification] The possibility of gas defects is evaluated by the time of occurrence of gas generation and gas floating calculated using the gas constant. The residual position of generated gases is decided by the closed loops indicating the final solidification location in the casting simulation. The above procedure enables us to suggest suitable casting designs with zero gas defects, without the need to repeat casting tests.

• 한국기계가공학회지
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• 제14권2호
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• pp.38-43
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• 2015

Tungsten inert gas (TIG) welding is commonly used in industries that require airtightness, watertightness, oiltightness, and precision. It is a non-consumable welding method that is commonly used for the welding of non-ferrous metals, but it can be used to weld most metals. The methods of TIG welding can be divided into three types. The first, manual welding is done directly on the metal by a welder with a torch. The second, semi-automatic welding, gets help from a material supplying machine, but it is conducted by a welder. Lastly, automated welding is conducted fully by a machine during its process and operation. Depending on the selection of electrode, the amount of heat that is applied to the base material and the electrode rod changes and makes the shape of welded parts different. A direct-current positive electrode was used for this study. Through the change of shielding gas type on a structural steel (SS-400) that is commonly used in industry, the composition and shape changes in welded parts were detected after welding. The heat-affected area, hardness value, and tensile strength were also identified through hardness testing and tensile testing. In this study, it was found that the higher hardness value of the heat-affected is, the weaker the tensile strength becomes.

• 전기화학회지
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• 제13권1호
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• pp.34-39
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• 2010

본 연구에서는 용융탄산염형 연료전지의 연료극 전극두께가 과전압에 미치는 영향을 $100\;cm^2$ 급 단위전지를 사용하여 검토하였다. 용융탄산염형 연료전지에서의 수소 산화속도는 충분히 빨라 전극면적이 성능에 크게 영향을 미치지 않을 수 있어, 본 연구에서는 전극의 기하학적 면적의 크기가 과 전압에 미치는 영향에 대해 연구하였다. 평가는 정상분극법과 비활성가스 계단형 첨가법 (ISA)와 반응물 첨가법 (RA)를 사용하여 연료극 두께 0.77 mm와 0.36 mm에 대해 수행하였다. 평가결과 두 전지에서 연료극 과전압이 거의 동일하게 관찰되어 연료극 두께에 의한 과전압의 차이는 발생하지 않았다.

• Journal of Advanced Marine Engineering and Technology
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• 제18권2호
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• pp.91-96
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• 1994

Intake gases other than air, which is composed of oxygen, nitrogen, carbon dioxide, and argon, are used to study their effects on the performance of the diesel engine experimentally. The engine is operated at constant speed and fixed fuel injection timing, and cylinder pressure and heat release rate are measured at various intake gas compositions. The results show that increase of oxygen concentration improves the performance of the engine generally. The adverse effect is observed when the oxygen concentration is increased over the critical oxygen concentration of this test, mainly because of the over-shortened ignition delay. Increase of carbon dioxide concentration degardes the performance of the engine, mainly due to the lower specific heat ratio of carbon dioxide. Adding argon gas to the intake gas improves the overall performance. Finally, it is found that two most influencing factors affecting the performance of the diesel engine in this study are ignition delay and speific heat ratio of the intake gas.

• 한국안전학회지
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• 제5권1호
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• pp.41-48
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• 1990

In this study the explosion characteristics of terephtalic acid dust(PTA) was investigated with the Hartmann type apparatus. The minimum ignition energy, minimum explosible concentration, flame propagation velocity, explosion pressure, explosion pressure rise rate and the effect of inert dust(talcum) on explosion characteristics were measured. Flame velocity was 50m/s at 700g/m$^3$ concentration, and the explosion pressure and explosion pressure rise rate were most likely with that of gas explosion. It was found that an inert dust acts as a heat sinker and it disturbs the combustion of flammable dust, as a result, explosion pressure and explosion pressure rise rate were decreased and minimum explosion concentration was increased with increasing the fraction of talcum dust in PTA.

• 한국화재소방학회논문지
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• 제28권3호
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• pp.34-42
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• 2014

본 연구에서는 $CH_4$ 및 $C_3H_8$ 연료의 컵버너 비예혼합화염에서 Swing, Rotation, Lifted 및 Blow-out과 같은 화염 불안정성을 발생시키는 불활성기체($N_2$, Ar, $CO_2$ 및 He)의 농도를 측정하였으며, 소화기준(즉, 화염날림 또는 화염불안정성 개시)에 따른 소화농도의 정량적 차이를 검토하였다. 소화농도의 차이는 부상화염의 발생 그리고 낮은 소화성능의 불활성기체일수록 증가됨을 확인하였다. 소화기준에 따른 소화농도의 최대 차이는 $C_3H_8$-air 비예혼합화염의 최대 연료유속의 조건(1.3 cm/s)에서 약 35%이다. 또한 화염 불안정성의 개시를 기준으로 측정된 소화농도는 정확한 그리고 경제적 설계 농도의 관점에서 유용한 정보를 제공할 것으로 기대된다.

• 한국화재소방학회논문지
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• 제18권2호
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• pp.12-19
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• 2004

지구 환경 보호를 고려한 불활성가스계의 혼합물인 IG-541소화제가 개발되었다. 소화제는 물성에 의한 특성 및 효율성, 환경에 미치는 영향뿐만 아니라 안정성, 경제성을 고려해야한다. 이러한 불활성 가스계의 대체 소화제에 사용되는 $N_2$, Ar, $CO_2$의 순수 및 혼합물의 물성을 수집하여 비교하였다. 불활성 가스계 대체소화제의 물성 중 밀도, 점도, 표면장력을 온도에 대한 변화와 혼합물에서 몰 분율의 변화에 관해 비교하였다. 3성분계 혼합물 중 50% $N_2$, 40% Ar, 10% $CO_2$(mol. %)의 조성인 혼합물에서 밀도가 높고, 점도가 낮으며, 표면장력이 순수 성분 보다 높지 않아 소화제로서 유리하다.

• Nuclear Engineering and Technology
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• 제53권8호
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• pp.2616-2628
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• 2021

The results of effective irradiation swelling in a wide range of burnup levels are numerically obtained for an inert matrix fuel, which are verified with DART model. The fission gas swelling of fuel particles is calculated with a mechanistic model, which depends on the external hydrostatic pressure. Additionally, irradiation and thermal creep effects are included in the inert matrix. The effects of matrix creep strains, external hydrostatic pressure and temperature on the effective irradiation swelling are investigated. The research results indicate that (1) the above effects are coupled with each other; (2) the matrix creep effects at high temperatures should be involved; and (3) ranged from 0 to 300 MPa, a remarkable dependence of external hydrostatic pressure can be found. Furthermore, an explicit multi-variable mathematic model is established for the effective irradiation swelling, as a function of particle volume fraction, temperature, external hydrostatic pressure and fuel particle fission density, which can well reproduce the finite element results. The mathematic model for the current volume fraction of fuel particles can help establish other effective performance models.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2018년도 춘계 학술논문 발표대회
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• pp.224-225
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• 2018

Modern people are more interested in the indoor environment as they spend more time indoors than in the past. Among the air pollutants in the indoor air, ladon gas is a colorless, tasteless, odorless, inert gas produced by nuclear decomposition of naturally occurring uranium in rocks and soils. It has been proven that ladon gas is introduced into the room through cracks on the floor of the building or basement wall, and it causes various diseases such as lung cancer when exposed to radon during human breathing. The US Environmental Protection Agency (EPA) specifies 4pCi / L as a necessary measure for radon, and the Korea Environmental Protection Agency has implemented comprehensive indoor radon management measures since 2007. Therefore, in this study, we intend to adsorb and reduce radon in indoor air pollutants.

• 대한화학회지
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• 제7권2호
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• pp.122-127
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• 1963

Pyrolysis fo polyethylene and polypropylene has been studied in order to clarify the mechanism of chain scission and effect of oxygen on degradation. Rate of weight decrease was measured under nitrogen and air atmosphere at constant temperature for the samples of high density polyethylene, low density polyethylene and isotactic polypropylene, and then gaseous hydrocarbons produced from pyrolysis were analysed by gas chromatography. Although there is little substantial difference between composition of hydrocarbon gases from pyrolysis of high density polyethylene and low density polyethylene except some difference in quantity of total gas produced, gas composition from polypropylene pyrolysis differs from that of polyethylene pyrolysis. Gases from pyrolysis under air contain much more unsaturated hydrocarbons than those from pyrolysis under inert gas.