• 대한기계학회논문집B
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• 제35권4호
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• pp.425-429
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• 2011

원자로의 노심 손상에 따른 노심 용융물의 노외 유출시 코어캐처라고 불리는 설비를 통해 용융물을 억제하고 냉각시키게 된다. 이 때 노외 노심용융물의 거동은 희생물질과의 반응을 포함한 복잡한 물리적, 화학적 현상에 의해 결정된다. 이 연구는 기존의 용융물 거동 실험결과에 대해 용융물의 유동과 열전달의 세부적인 특성을 상용코드를 이용해 해석하여 검증함으로써 코어캐처의 설계에 활용할 수 있도록 하기 위한 것이다. 단순화된 채널에서 시간에 따른 용융물과 공기의 이상유동과 복사열전달을 VOF 모델과 구분종좌법을 적용하여 비정상상태에서 해석한 결과, 열전달에 따른 용융물 내부의 온도 변화 및 이에 따른 점성 변화 등을 예측할 수 있음을 확인하였다. 이러한 접근방식을 기초로 향후 용융물의 조성, 유량 및 용도 등의 조건에 따른 용융물의 거동에 대한 자세한 평가가 필요하다.

• 대한기계학회논문집B
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• 제29권5호
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• pp.590-598
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• 2005

The present study has been conducted to investigate the effect of discrete ribs and rotation on heat/mass transfer characteristics in a two-pass square duct with $90^{\circ}-rib$ turbulators. The rib turbulator has a square cross section of 1.5 mm. The rib height-to-hydraulic diameter ratio $({e/D_{h})$ is 0.056, and the rib pitch-to-rib height ratio (p/e) is 10. The gap width is the same as the rib height. The rotation number ranges from 0.0 to 0.2 while Reynolds number is fixed to 10,000. In a stationary duct, the heat/mass transfer on the surfaces with discrete ribs is enhanced because the gap flow promotes local turbulence and flow mixing near the ribbed surface. In a rotating duct, the gap flow affects differently the heat/mass transfer on leading and trailing surfaces with discrete ribs. On the leading surface of the first pass, heat/mass transfer is increased due to the gap flow. On the trailing surface of the first pass, however, heat/mass transfer is decreased because the gap flow disturbs reattachment of main flow. The phenomenon, that is, the difference of heat transfer between the leading and the trailing surfaces is distinctly presented by rotation.

• 한국의류학회지
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• 제33권11호
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• pp.1806-1816
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• 2009

This study analyzes the efficiency of a solar cell attached to an air circulation jacket. A commercially available silicon solar panel was selected and attached at four spots where the body angle was $40-60^{\circ}$ and voltage ($V_{oc}$, V), current ($I_{sc}$, A), and output power (P, W) were measured to determine the efficiency. The solar panel was applied to the outer jacket that operates with two fans to increase the convection that lowers the body temperature. The heavy work of standing, walking, and sweeping of a street sweeper was simulated in the field test. The microclimate within the jacket (with or without a fan) was measured and the subjective thermal, humidity, and comfort sensations were surveyed. SPSS 12.0 statistical package was used for a t-test and Wilcoxon signed-rank test. The results show that the highest efficiency of the solar cell was at the incident angle of $60^{\circ}$ in terms of voltage, current and output power distribution. The microclimate temperature of the air circulation jacket decreased significantly with the high power of the fan and subjects felt cooler than the jacket with a fan at the incident angle of $60^{\circ}$. Air circulation jackets operated by a silicon solar panel showed a significant cooling effect on the wearers.

• 한국수정란이식학회지
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• 제28권3호
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• pp.265-271
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• 2013

Cryopreservation and in vitro fertilization (IVF) protocols are important in genetic studies and applications to transgenic animals. Various studies about boar sperm cryopreservation have been studied for a long time. Those were about the use of extenders, the choice of sugars, the cooling and warming rates. The factors that influence the boar sperm are the dramatic changes in temperatures, osmotic and toxic stresses, and reactive oxygen species (ROS) generation. Among these factors, ROS generation is the main damage to DNA which is a principal genetic material and the most important for the practical applications. So we wondered whether ROS generation could be reduced. In previous study, monothioglycerol (MTG) was essential for the culture of embryo stem cells. Therefore we added MTG in the freezing extender based on lactose-egg yolk (LEY) with trehalose. For the assessment of the frozen-thawed sperm, we focused onmotility, membrane integrity and DNA damage. First, we used a computer-aided sperm analysis system for overall conditions of sperm such as motility and viability. Then we performed the sperm chromatin structure assay for DNA integrity and hypo-osmotic swelling test for membrane integrity. And our result showed the existence of MTG in the freezing extender caused less damage to DNA and higher motility in frozen-thawed boar sperm. Also we checked a relative antioxidant activity of MTG in modified Modena B extender. We concluded that this reagent can activate sperm mitochondria at MTG $0.2{\mu}M$, contribute to sperm motility and DNA integrity but there was no significant difference on membrane integrity. Also antioxidant activity of MTG in modified Modena B extender was proved.

• 한국정밀공학회지
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• 제17권9호
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• pp.189-195
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• 2000

RP techniques have their unique characteristics according to the working principles : star-stepped surface of parts due to layer-by-layer stacking low build speed caused by line-by-line solidification to fish one layer and post processing to improve surface finish etc The objective of this study is to propose a new RP technique Variable Deposition Mnanufacturing (VDM) which can make up for the disadvantages of the existing RP techniques and to develop an apparatus to implement the technique. The proposed process can greatly reduce the build time and improve the surface finish of parts generated. Experiments are carried out to obtain the range of temperature of molten material to maintain its fluidity and to investigate the effect of gas cooling on the preservation of the slopes. Some simple shapes such as a line-shape an S-shape and a circle-shape are fabricated from Ethylene Vinyl Acetatecopolymer(EVA) In order to examine the applicability of VDM to more general shapes a tensile specimen and a yo-yo shape were manufactured by the proposed RP method using EVA material as a trial approach. The current basic study shows a high potential of practical use of the proposed VDM process to prototyping of a general three-dimensional shape.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2010년도 춘계학술발표대회 초록집
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• pp.60-60
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• 2010

Since the curved hull plate was made by a series of manufacturing process including cold bending, manual local heating and correction work, the accuracy of curved plate strongly depends on the proficiency of worker. So the demands on the automatic local heating system for curved hull plate have continuously increased and the various researches relevant to it have been performed. Generally, the heat sources used for local heating were flame and induction heat. In terms of initial cost, flame heating is in a better favorable position than induction heating. However, from the viewpoint of the control of heat, induction heating has more advantage. So the various researches related to apply the induction heating to the automatic forming system has been performed. The purpose of this study is to establish the proper capacity of high frequency induction heating system for forming the curved hull plate. In order to do it, the proper coil shape for local heating was designed and the efficiency of induction heating system was determined by comparing of temperature results obtained by FEA and experiment. With the results, the extensive FEA was performed to identify the effect of heated plate dimension, cooling method and the capacity of induction heating system on the amount of heat loss introduced by induction heating. Based on the results, the proper capacity of high frequency induction heating system was proposed.

• 한국화재소방학회논문지
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• 제25권3호
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• pp.51-56
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• 2011

도로터널에서의 미분무수 소화시스템의 화재진압 특성을 조사하기 위해 실물 터널 화재 실험을 수행하였다. 적용된 소화시스템은 압력이 3.5 bar인 저압 물분무 소화설비와 60 bar인 고압 미분무수 소화시스템이다. 미분무수 소화시스템은 물분무 소화시스템의 1/6 만큼의 소화용수량을 사용한다. 화원 (fire source)은 실물 승용차와 유류화재를 모사한 화원면적 $1.4m^2$의 헵탄 연료 팬 화재로 구성하였다. 터널 내의 환기조건을 구현하기 위해 실물모형 터널의 한쪽 끝단에 유속(0.9~3.8 m/sec 범위) 발생장치를 설치하였으며, 화원에서 하류 방향으로 터널 내 온도분포는 K-type 열전대 트리를 사용하여 측정하였다. 실험 결과 고압 미분무수 소화시스템은 B급 화재의 경우 저압 물분무 시스템과 동등한 수준의 냉각효과를 보였다.

• 한국축산식품학회지
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• 제40권2호
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• pp.197-208
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• 2020

The effects of presalting conditions (storage temperature and duration) with/without sodium tripolyphosphate (STPP) on the color and pigment characteristics of cooked ground chicken breast were investigated. Meat mixtures containing 2% NaCl (control) or 2% NaCl and 0.5% STPP (STPP treatment) were stored for 0, 3, 5, 7, and 10 d at 2℃ or 7℃, followed by cooking to 75℃, and cooling and storage at 2℃-3℃ until further analysis. The treatment was the most effective on the pink color defect of all independent variables. The effect of storage temperature was only observed on CIE L^⁎ values and percentage myoglobin denaturation (PMD). The control was redder than the STPP treated samples and the CIE a^⁎ values increased (p<0.05) from 0 to 5 d in the control and STPP treated samples. Compared to the STPP treatment, the control exhibited increased reducing conditions (more negative oxidation reduction potential), lower undenatured myoglobin, and greater PMD. No differences in the cooking yields of the control and STPP-treated samples were observed for various storage durations. Products with STPP showed higher (p<0.05) pH values than those without STPP, but no differences (p>0.05) in PMD were observed over the storage period in the control and STPP treated samples, except for day 0. Thus, STPP is effective at reducing the pink color in cooked chicken breasts. In addition, presalting for longer than 5 d resulted in increased pink color of the cooked chicken breasts.

• 한국결정성장학회지
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• 제26권4호
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• pp.150-154
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• 2016

$K_2Ti_6O_{13}$ 휘스커를 합성하는 방법은 고상법, 수열합성법, 소성법, 융제법, 서냉법, 용융법, KDC법, 졸-겔법 등이 있다. 융제법을 이용하여 $K_2Ti_6O_{13}$을 합성하는 연구를 진행하였다. 칼륨 전구체의 종류와 반응온도와 시간을 조절하여 합성 된 $K_2Ti_6O_{13}$의 입자크기와 분포를 제어하였고, 합성된 $K_2Ti_6O_{13}$의 평균입자 크기는 $500nm{\sim}2{\mu}m$였다. KOH와 $TiO_2$의 비율, pH(KOH 첨가량), 반응온도와 반응시간 등의 공정변수에 대해 연구를 진행하였다. 합성된 $K_2Ti_6O_{13}$은 X-선 회절분석기와 전계방사 주사전자현미경을 이용하여 특성평가를 실시하였다.

• 한국지구과학회지
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• 제26권6호
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• pp.560-572
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• 2005

이 연구에서는 1979년부터 1999년까지 21년 동안에 한반도 겨울철 한파와 관련된 대기 순환 및 열원$(Q_1)$의 분포 특성을 조사하였다. 한파 발생 빈도는 1년간 약 1개로 나타났으며, 1989년을 중심으로 전반기에 전체의 $60\%$가 발생하였다. 한파 발생 동안 하층의 대기 순환 패턴은 평년에 비해 서고동저형의 기압 패턴이 더 뚜렷하며, 상층에서도 한반도에 기압골의 영향이 더 강하게 나타난다. 한파가 발생하는 동안에 한반도 부근의 기온 하강 패턴은 바이칼호 부근의 기온 패턴과 반대로 나타나며, 기온의 연직 구조에서도 400 hPa을 기준으로 하층과 상층의 기온 편차는 반대로 나타난다. 열원에 대한 분석은 한파 발생 시 한랭 이류에 의한 냉각은 하강 운동에 의한 단열 승온에 의해 균형을 이룬다는 것을 보여주는데, 이것은 한랭 핵의 이동이 열흡수원의 이동 경로와 연관되어 있음을 나타낸다. 따라서 한파의 유지 기작을 이해하고 한파를 예측하기 위해서는 열원 그리고 열흡수원의 이동 기작이 밝혀져야 할 것이다.