• 대한전기학회논문지
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• 제35권1호
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• pp.17-25
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• 1986

Discussions on this paper are related to the effects of organic materials to treeing phenomena of low density polyethylene. As additives, 11 kinds of organic compounds are selected by considering the respective features such as melting point, boiling point, electron affinity as well as molecular structure, and then the specimens of low density polyethylene are prepared by blending with 10wt% of the selected additives. For the comparison of effectiveness of treeing resistance and interpretation of the mechanism of compounds as treeing retardants, several investigations such as the tree acceleration test, the prestressed test and the measurement of internally occurred partial discharge are carried out. As the results, meta-Cresol is regard as the most effective retardant among those, and it is supposed that this aromatic compound to be comprised of radical having large electron affinity has strong capability to accept energetic electron to prevent or delay the growth of discharge streamer. Furthermore, by activating partial discharge at the wall of tree pit through the function of trapped electron at this material, the gas pressure in the pit is increased up to prevent the growth of streamer.

• 한국초전도ㆍ저온공학회논문지
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• 제10권4호
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• pp.38-42
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• 2008

Miniature J-T cryocooler using nitrogen or argon has been widely adopted in cooling infrared sensor for space/military application and cryosurgery. Argon or nitrogen, however, has relatively low specific cooling power compared to nitrous oxide, but the ultimate operating temperature is much lower than nitrous oxide. On the other hand, nitrous oxide has large specific cooling power, but the operating temperature is limited to its boiling point (>183K). To compromise the different characteristics of these gases, the performance of miniature J-T cryocooler using argon and nitrous oxide mixture is investigated in this paper. Three different compositions of mixture (25/75, 50/50, and 75/25 molar fraction) are blended and tested. The results are compared with the experiments of pure argon and pure nitrous oxide. The experimental results show some encouraging potentiality of mixed refrigerant J-T cryocooler. The critical clogging problem, however, was observed with argon and nitrous oxide mixture, and the lowest achievable temperature with this mixture was limited to the freezing point of nitrous oxide. The paper discusses detailed clogging process of the mixture and suggests an alternative.

• 한국재난정보학회 논문집
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• 제19권3호
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• pp.532-544
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• 2023

연구목적: 신규로 사용되는 바이오연료를 기존 연료와 혼합하여 사용하는 경우 발생하는 위험성과 물성 변화를 열분석 방법(DSC, TGA)을 사용하여 화학 화재의 원인물질의 위험성을 확인하고, 평가할 방법과 그에 따른 물질의 위험성 관련 데이터를 확보함으로써 화재 원인 감식과 감정에 활용하기 위함이다. 연구방법: 본 실험에 사용된 연구 방법으로는 시차주사열량계(DSC : Differential Scanning Calorimeter)에 의하여 피크의 위치, 모양, 개수, 피크의 면적으로부터 열량 변화의 정량적인 정보를 통하여 열유속 차이(Difference in heat flux)를 측정하였고, 열중량분석(TGA : Analyzer)을 시행함으로써 특정한 온도에서 분해열 등에 의해 발생한 무게 변화를 연속적으로 측정하였다. 연구결과: 먼저 열 유속의 그래프에서 물질의 끓는점과 물질이 가지고 있는 고유 특성치 또는 분해에 필요한 에너지를 확인할 수 있다. 둘째 바이오디젤의 함량이 증가할수록 많은 피크를 확인 할 수 있었다. 셋째 비점이 낮은 물질들이 함유하고 있다는 것을 분석 결과로 확인할 수 있었다. 결론: 현재 새로운 에너지원으로 사용되고 있는 바이오디젤의 위험성을 다양한 물리·화학적 분석기법(DSC+TGA)을 통하여 사용함으로써 물질의 물적 위험성을 평가할 수 있음을 보여주었다. 아울러 본 연구의 시험방법별 차이의 비교와 실험에 대한 노하우를 축적하고 활용한다면 향후 위험물의 물성 연구와 물질 위험성 평가 연구에 있어 도움이 되리라 기대한다.

• 분석과학
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• 제7권3호
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• pp.329-338
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• 1994

기체 크로마토그래피에 의한 단일 컬럼상에서 천연가스 성분의 용리거동을 알아보았다. 천연가스 성분의 용량인자인 k'값을 결정하기 위하여 불감시간 $t_0$를 동족계열에 의한 외삽법으로 구하였다. 여러 가지 온도에서 $C_1$부터 $C_5$까지 동족계열의 머무름 시간을 탄소수에 대해서 도시하면 어느 한 점에 수렴하게 되는데, 이 점을 $t_0$로 정하였다. n-부탄을 기준으로 온도에 따른 컬럼효율의 변화를 알아본 결과 온도가 증가할수록 컬럼효율은 증가하였으나, 분리시간이 짧은 시료들의 분리도는 감소하였다. 28% DC-200 정지상에서 흡착엔탈피 변화값을 구하였고, 천연가스 성분들의 머무름 메카니즘을 알아보기 위해 log $t_R$, log k' 및 log ${\alpha}$값을 van der Waals 부피(Vw), 분자간 연결지수(X) 및 소수성 계열상수(f)와의 희귀분석을 수행한 결과 log k'과 Vw 및 f가 높은 상관관계를 보여 주었다. 천연가스 성분의 물리적 성질과 물리적 파라미터와의 상관관계를 알아본 결과는 Vw는 분자량과 발열량(${\Delta}H_{comb}$), X는 끓는 점, f는 분자량, 끓는 점 및 발열량과 상관계수가 0.99 이상으로 높은 상관관계를 나타내었다. Vw와 발열량과의 회귀방정식을 이용하여 $C_6$호부터 $C_{10}$까지의 발열량을 예측한 결과 문헌값과 0.2%의 상대오차 범위내에서 일치하였다.

• Carbon letters
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• 제25권
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• pp.78-83
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• 2018

Pyrolyzed fuel oil (PFO) and coal tar was blended in the feedstock to produce pitch via thermal reaction. The blended feedstock and produced pitch were characterized to investigate the effect of the blending ratio. In the feedstock analysis, coal tar exhibited a distinct distribution in its boiling point related to the number of aromatic rings and showed higher Conradson carbon residue and aromaticity values of 26.6% and 0.67%, respectively, compared with PFO. The pitch yield changed with the blending ratio, while the softening point of the produced pitch was determined by the PFO ratio in the blends. On the other hand, the carbon yield increased with increasing coal tar ratio in the blends. This phenomenon indicated that the formation of aliphatic bridges in PFO may occur during the thermal reaction, resulting in an increased softening point. In addition, it was confirmed that the molecular weight distribution of the produced pitch was associated with the predominant feedstock in the blend.

• 수산해양교육연구
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• 제28권3호
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• pp.713-726
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• 2016

This study were attempted to apply the HACCP system adopted in the dried anchovy workplace to ensure the hygiene safety of dried anchovy workplace. In this study, HACCP system procedures, including HACCP team organization, determination of critical control point(CCP), establishment of critical limits, mornitering and verification etc., were established using KFDA 12 procedures. To determine whether hazards were critical elements, we evaluated the likelihood and seriousness of each hazard element. The likelihood of residual microorganism and metal piece exceeding the acceptable limit in dried anchovy products were demonstrated to be a critical hazard element. Management of the boiling(CCP-1B) and metal detection(CCP-2P) were determined to be a critical control point. The standards for acceptable residual microorganism and metal piece were set based on relevant laws and regulations, and then the limits were adapted and established for the CCP. An HACCP plan applicable to dried anchovy workplace was established.

• 한국물환경학회지
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• 제37권3호
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• pp.175-189
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• 2021

In this study, 48 streams in the Sapgyo Watershed were selected, and the Load Duration Curves (LDC) were drawn up for each stream using water quality and flow monitoring over the last three years (2018-2020), and it was evaluated whether the target water quality was achieved for each flow section. As a result of evaluating whether or not the target water quality exceeded according to the LDC, it was found that 22 rivers exceeded the target water quality. Five rivers exceeded the target water quality due to point pollutant sources, 13 rivers exceeded the target water quality due to non-point pollutant sources, and 4 rivers exceeded the target water quality due to both point and non-point pollutant sources. Among the rivers that exceeded the target water quality due to point pollutant sources, which included domestic sewage of the untreated population, there is a need to reduce the influx of polluted loads by the untreated population. The use of eco-friendly fertilizers is recommended for rivers with a relatively high farmland ratio among rivers exceeding the target water quality due to non-point pollutant sources, and installation of boiling point reduction facilities that can reduce the amount of polluted load introduced during rainfall or manage water shores. In rivers with a large number of livestock breeding heads, the livestock houses located in these rivers need to be preferentially transferred to livestock manure treatment plants. Due to the high ratio of land area because of urbanization, initial rainwater treatment facilities are required to reduce the amount of pollutant load flowing into the river through the impermeable layer during rainfall.

• 대한의용생체공학회:의공학회지
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• 제16권1호
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• pp.67-76
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• 1995

Explosive evaporative removal process of biological tissue by absorption of a CW laser has been simulated by using gelatin and a multimode Nd: YAG laser. Because the point of maximun temperature of laser-irradiated gelatin exists below the surface due to surface cooling, evaporation at the boiling temperature is made explosively from below the surface. The important parameters of this process are the conduction loss to laser power absorption (defined as the conduction-to-laser power parameter, Nk), the convection heat transfer at the surface to conduction loss (defined as Bi), dimensionless extinction coefficient (defined as BrJ, and dimensionless irradiation time (defined as Fo). Dependence of Fo on Nk and Bi has been observed by experiment, and the results have been compared with the numerical results obtained by solving a 2-dimensional conduction equation. Fo and explosion depth (from the surface to the point of maximun temperature) are increased when Nk and Bi are increased. To find out the minimum laser power for explosive evaporative removal process, steady state analysis has been also made. The limit of Nk to induce evaporative removal, which is proportional to the inverse of the laser power, has been obtained.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.316-321
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• 2003

The spatter and porosity could be occurred during $CO_2$ CW laser welding of Primer-coated Steel for Shipbuilding. This study has suggested an alternative idea by examining of weld-defect formation mechanism. The primer-coated plate has caused the spatter, humping bead and porosity and these are main part of the welding defect, attributed to the powerful vaporizing pressure of primer attached on the base metal. The zinc of primer has a boiling point that is the lower temperature than melting point of steel. Zinc va}X)f will build up at the interface between the two sheets and this tends to deteriorate the quality of the weld by ejecting weld material from lap position or leaving porosity. Therefore introducing a small gap clearance in the lap position, the zinc vapor could escape through it and sound weld beads can be acquired. In conclusion, we suggested the occurred and prevented mechanism of weld defects with searching the factor.

• 한국화재소방학회논문지
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• 제11권4호
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• pp.15-23
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• 1997

A series of measurements and visualization to investigate the extingushiment of water sprays with pool fires is presented. Fire source is a small-scale pool burner with methanol, ethanol and gasoline. Measurements of temperature, O2, CO2, and CO concentrations along the plume centerline are carried out to observe pool structures without water sprays. Visualization by the Ar-ion laser sheet flow pattern of droplets of the sprays above the pool fires. It is observed than in the case of methanol and ethanol, water sprays continuously penetrate into the center of fuel surfaces. The gasoline pool fire allows intermittent penetration of water sprays because of pulsating characteristics of the gasoline flame. To evaluate the cooling effect of the fuel surface by the sprays, the temperature was measured at the fuel surface. As soon as the mists reach the fuel surface of methanol and ethanol, the temperatures of the fuel surface decrease rapidly below the boiling point, and then the fires are extinguished. Due to the application of mist upon the gasoline fire, though the fuel temperature decrease abruptly at the time of the injection, such a repid decrease do not continue till the extinction point.