• Journal of Mechanical Science and Technology
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• 제15권11호
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• pp.1533-1540
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• 2001

A high-temperature sodium stainless steel heat pipe was fabricated and its performance has been investigated. The working fluid was sodium and it was sealed inside a straight tube container made of stainless steel. The amount of sodium occupied approximately 20% of the total volume of the heat pipe and its weight was 65.7gram. The length of a stainless steel container is 1002mm and its outside diameter is 25.4mm. Performance tests were carried out in a room air condition under a free convective environment and the measured temperatures are presented. The start-up behavior of the heat pipe from a frozen state was investigated for various heat input values between 600W and 1205W. In steady state, axial temperature distributions of a heat pipe were measured and its heat transfer rates were estimated in the range of vapor temperature from 50$0^{\circ}C$ to 63$0^{\circ}C$. It is found that there are small temperature differences in the vapor core along the axial direction of a sodium heat pipe for the high operating temperatures. But for the range of low operating temperatures there are large temperature drops along the vapor core region of a sodium heat pipe, because a small vapor pressure drop makes a large temperature drop. The transition temperature was reached more rapidly in the cases of high heat input rate for the sodium heat pipe.

• 한국추진공학회지
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• 제8권4호
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• pp.16-25
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• 2004

구리분말 소결윅 히트파이프의 열수송 한계를 예측하는 이론적 해석을 수행하였다. 히트파이프의 직경은 8 mm이고 물을 작동유체로 사용하였다. 입자의 직경을 대표적인 5 가지로 분류하여 각각의 유효 모세관 반경($r_c$) 기공률($\varepsilon$), 투파율(K)을 토대로 작동온도와 윅 두에 그리고 경사각에 따른 모세관압력과 열수송 한계, 열저항을 분석하였다. 소결윅의 모세관한계는 입자 직경이 크고 윅 두께가 증가하며 작동온도가 높을수록 증가했다 기공률과 모세관 반경이 증가할수록 열수송 한계가 높아졌으며, 윅 두께가 증가함에 따라 열저항이 크게 상승하였다.

• 한국산업보건학회지
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• 제25권3호
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• pp.301-311
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• 2015

Objectives: Operators of overhead traveling crane in a ship assembly factory perform work to transmit large vessel blocks to an appropriate working process. Hazardous matters such as metal dusts, carbon monoxide, carbon dioxide, ozone, loud noise and fine particles are generated by variable working activities in the factory. The operators could be exposed to the hazardous matters during the work. In particular, welding fumes comprised of ultra fine particles and heavy metals is extremely hazardous for humans when exposing a pulmonary through respiratory pathway. Occupational lung diseases related to welding fumes are increasingly on an upward tendency. Therefore, the objective of this study is to assess properly unknown occupational exposure to the welding fumes among the operators. Methods: This study intended to clearly determine an equivalence check whether or not chemical constituents and composition of the dusts, which existed in the driver's cab, matched up with generally known welding fumes. Furthermore, computational fluid dynamics program(CFD) was used to identify a ventilation assessment in respect of a contamination distribution of welding fumes in the air. The operators were investigated to assess personal exposure levels of welding fumes and respirable particulate. Results: The dust in an operation room were the same constituents and composition as welding fumes. Welding fumes, which caused by the welding in a floor of the factory, arose with an ascending air current up to a roof and then stayed for a long time. They were considered to be exposed to the welding fumes in the operation room. The personal exposure levels of welding fumes and respirable particulate were 0.159(n=8, range=0.073-0.410) $mg/m^3$ and 0.138(n=8, range=0.087-0.178) $mg/m^3$, respectively. They were lower than a threshold limit value level($5mg/m^3$) of welding fumes. Conclusions: These findings indicate that an occupational exposure to welding fumes can exist among the operators. Consequently, we need to be keeping the operators under a constant assessment in the operator process of overhead traveling crane.

• 한국전산유체공학회지
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• 제21권2호
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• pp.54-61
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• 2016

When spent fuel assemblies from the reactor of nuclear power plants(NPPs) are transported, the assemblies are exposed to short-term operations that can affect the peak cladding temperature of spent fuel assemblies. Therefore, it needs to perform the analysis of heat transfer on spent fuel dry cask during the operation. For 3 dimensional computational fluid dynamnics(CFD) simulation, it is proposed that the short-term operation is divided into three processes: Wet, dry, and vacuum drying condition. The three processes have different heat transfer mode and medium. Metal transportation cask, which is Korea Radioactive Waste Agency(KORAD)'s developing cask, is evaluated by the methods proposed in this work. During working hours, the boiling at wet process does not occur in the cask and the peak cladding temperatures of all processes remain below $400^{\circ}C$. The maximum peak cladding temperature is $173.8^{\circ}C$ at vacuum drying process and the temperature rise of dry, and vacuum drying process occurs steeply.

• 대한기계학회논문집B
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• 제36권9호
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• pp.953-960
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• 2012

AMTEC기술은 열을 직접 전기로 변환시키는 기술로서 소디움을 작동유체로 사용하고 있으며, 작동유체의 순환은 모세관윅을 사용한다. 순환계통에는 증발부윅, 순환윅 및 응축부윅으로 구성되고, 각각의 윅은 소디움의 액체 또는 증기가 순환하면서 압력손실이 발생하므로 소디움의 순환을 위해서는 증발부윅의 모세관압력이 윅내의 총압력손실보다 커야만 한다. 본 연구에서는 100 watt급의 AMTEC시제품설계을 위해 소디움의 순환계통으로 구성되는 증발부윅, 순환윅 및 응축부윅에서의 압력손실과 증발부에서 응축부로의 열손실을 순환윅의 직경과 길이에 대해 분석하여 증발부윅의 소결입자 직경과 순환윅의 설계에 활용하코저 하였으며, 분석결과에서 순환계통의 총압력손실보다 큰 모세관압력을 위해서는 증발부윅의 소결입자크기는 10 ${\mu}m$이 적합한 결과를 얻었다.

• 항공우주기술
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• 제12권2호
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• pp.108-117
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• 2013

가스발생기용 산화제 개폐밸브는 파일롯 공압으로 포핏을 열고 스프링 힘에 의해 닫음으로써 로켓엔진의 추진제 유량을 제어한다. 현재 개발 중인 산화제 개폐밸브는 액추에이터에서 압력을 제거하면 닫히도록 설계되어 있다. 그러므로 밸브의 성능을 평가하기 위해 밸브가 열리고 닫히는 특성에 따라 힘 평형 상태를 분석할 필요가 있다. 밸브가 닫히기 시작하는 시점의 작동 유체의 압력을 결정하고, 포핏이 열리는 시점의 압력을 결정되어 힘평형이 설계되어 있다. 인증시험 수준에서의 극저온 유동 시험 하에서 채터링 현상은 금속 기밀부에서 다량의 누설이 발생했다. 힘평형 계산을 이용한 산화제 밸브의 채터링이 발생된 시점의 압력은 약 11 bar로 예측 된다.

• 한국산업보건학회지
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• 제15권3호
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• pp.166-175
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• 2005

Health effects associated with metal working fluid (MWF) exposures include dermatitis, respiratory disease, hypersensitive pneumonitis, and asthma. Frequently, occupational exposures to MWFs are controlled by ventilating an enclosure with an air cleaning unit that includes a fan preceded by various kinds of filtration. There are several kinds of air cleaning units used in machining centers. But the associated troubles have hindered from efficiently using these devices. The main problem is the relatively short period of filter replacement. The reason is that the air cleaning units usually do not have the de-oiling systems, thus leading the earlier clogging of filters and reducing the flow rate of hood. Thus, the first stage of study was conducted to overcome this problem by developing the new oil mist collector equipped with the easy de-oiling system. The principle of de-oiling is that the centrifugal force generated by spinning the drum covered by filter fabric separates oils from the filter fabric. It would be very similar to the spin-dry laundry. By adopting this de-oiling technique, the problems associated with the conventional oil mist collectors could be solved. Several tests/analyses were performed to make the lab-scale oil mist collector. The collection efficiencies and the de-oiling efficiencies of commercially available filter fabrics were tested. Subsequently, the endurance test were conducted by observing SEM photos of filter fabrics and measuring tensile strength/expansion coefficient after spinning the filter drum for 20 minutes at the different rotation speeds. By doing these experiments, the most appropriate filter fabric and rotation speed/duration were selected. Finally, the new oil mist collector was designed. In the near future, this device must be tested in the real machining center.

• 한국산학기술학회논문지
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• 제18권3호
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• pp.724-729
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• 2017

회전익항공기용 연료탱크의 중요한 성능 중의 하나인 내충격성능은 충돌충격시험을 통해 검증된다. 충돌충격시험은 작용하는 하중이 매우 높기 때문에 실패 위험이 큰 시험인데, 만약, 연료탱크가 내충격 요구조건을 불만족하게 되면 항공기 전체 개발 일정에 심각한 차질을 줄 수 있다. 따라서, 초기 설계단계부터 연료탱크 충돌충격시험에 대한 수치해석을 수행하여 실물시험에서의 실패 가능성을 최소화 하려는 노력이 수행되어 왔다. 최근, 국내개발 회전익항공기의 항속거리를 증가시키기 위한 목적으로 외부 보조연료탱크 개발이 진행되고 있다. 본 연구에서는 해당 외부 보조연료탱크의 내충격 성능의 검토를 위해 현재까지 진행되어 온 충돌충격시험에 대한 수치해석 결과를 제시하였다. 수치해석 방법으로는 유체-구조 연성해석 방법인 입자법을 적용하였고, 미군사규격에서 규정하고 있는 시험조건을 해석조건으로 반영하였다. 또한, 실물 연료탱크 소재의 시편시험을 통해 기 확보된 바 있는 물성데이타를 수치해석에 적용하였다. 그 결과로 연료탱크 외피 및 피팅 부위의 등가응력을 계산하고 내부 장착품의 거동과 작용 하중을 분석함으로써 외부 보조연료탱크의 내충격성 설계를 위한 데이터 확보 가능성을 확인하였다.