• 한국도로학회:학술대회논문집
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• 한국도로학회 2010년 추계학술대회 논문집
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• pp.171-174
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• 2010

• 설비공학논문집
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• 제22권10호
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• pp.710-718
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• 2010

A numerical study was performed to predict refrigerant charge amount in a mini-channel condenser for a R410A residential air-conditioning system. Multi-channel flat tubes with 12 mini-channels of 1.17 mm average hydraulic diameter for each tube were applied to the condenser. The condenser consisted of 3 passes, and the first, second, and third pass had 44, 19, and 11 tubes, respectively. Each pass was connected by a vertical header. In this study, the condenser was divided into 410 finite volumes, and analyzed by an $\varepsilon$-NTU method. With thermophysical properties and void fraction models for each volume element, the R410A amount distribution and a total charge amount in the condenser were calculated. The predicted total charge amount was compared with the experimentally measured charge amount under a standard ARI A condition. The developed model could predict the charge amount in the mini-channel condenser within prediction errors from -23.9% to -3.0%. Air velocity distribution at the condenser face was considered as non-uniform and uniform by the simulation model, and its results showed that the air velocity distribution could significantly influence the charge amount and vapor phase distribution in the condenser.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1997년도 가을 학술발표회 논문집
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• pp.313-318
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• 1997

Air voids existed in hardened concrete have an important influence on concrete deterioration such as carbonation, freezing and thawing, and corrosion of embedded steel in concrete. Therefore it is very significant to investigate the pore structure of system (size, number and continuity of air voids) to solve the reason caused concrete deterioration. The purpose of this study is to develop th standard method of measuring air voids which affect properties in hardened concrete using image analyzing system. This paper presents the settlement of rapid and exact experimental method which extracts fine bubbles, calculates the number of air voids, and determines air-voids distributions using image analyzing system with computer.

• 콘크리트학회논문집
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• 제23권6호
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• pp.701-709
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• 2011

콘크리트의 공극구조를 평가하기 위한 대표적인 모델 중 하나가 Power가 제안한 간격계수(SF : spacing factor)인데, 이 PSF(power spacing factor)는 평균단일공극 개념을 사용하여 갇힌 공극의 존재 여부에 따라 그 결과값이 실제와 상이하게 나올 수 있는 단점이 있다. 이에 이 연구에서는 실측된 공극 간격 데이터를 이용하여 지수화한 AMSF(실측간격계수 : actual measurement spacing factor)를 개발하였으며, 콘크리트 혼합물의 화상 분석 결과를 이용하여 PSF와 AMSF를 비교 평가하였다. 이 연구 결과, PSF와 AMSF는 전반적으로 유사한 경향을 나타내고 있으나, PSF가 $400{\mu}m$ 이상일 때 전반적으로 AMSF가 좀 더 큰 값을 나타내고 있어, 공기량이 작은 콘크리트 혼합물의 경우 PSF는 실제보다 좀 더 작은 값으로 예측할 가능성이 있는 것으로 나타났다. 또한 갇힌 공극의 유무에 따른 PSF와 AMSF 각각을 분석한 결과, AMSF는 갇힌 공극을 포함하지 않고 분석한 값이 더 크게 나타났고, PSF는 실제와 다르게 갇힌 공극을 포함하지 않고 분석한 값이 더 작게 나타났다. 이와 같이 PSF가 이와 같은 경향을 나타내는 이유는 평균단일공극 개념을 사용하기 때문이며, 이 분석 결과를 통해 AMSF가 좀 더 실제에 가까운 분석기법임을 확인할 수 있었다.

• Journal of Electrical Engineering and Technology
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• 제1권4호
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• pp.528-533
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• 2006

Electrical discharges may occur in gas, liquid as well as solid insulating materials. This paper describes the investigation results on the discharges in air, silicone oil and low density polyethylene (LDPE) using needle plane electrode system under AC voltage of 50 Hz. The experimental results showed that for discharge in air (corona), discharge pulses were concentrated around the peak of applied voltage at negative half cycle. For silicone oil positive as well as negative discharges were observed which concentrated around the peak of applied voltage. The positive pulse number was smaller but the magnitude was higher than that of negative discharge. Discharges in void took place at wider range of phase of applied voltage. The unbalance in pulse number and magnitude similar to that of oil discharges were observed. For electrical treeing in LDPE, the discharges were spread before the zero cross of the applied voltage up to the peak at both positive and negative half cycles. The discharge pulse sequence analysis indicated that the PD occurrence in air, oil and void were strongly affected by the magnitude of applied voltage. However, for electrical treeing it was observed that the discharge occurrence was strongly affected by the time derivative of the applied voltage (dv/dt).

• KIEAE Journal
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• 제10권3호
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• pp.89-96
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• 2010

In comparison with ordinary or heavy-weight concrete, light-weight air void concrete has the good aspects in optimizing super tall structure systems for the process of design considering wind load and seismic load by lightening total dead load of buildings and reducing natural resources used. Light-weight air void concrete has excellent properties of heat and sound insulating due to its high amount porosity of air voids. So, it has been used as partition walls and the floor of Ondol which is the traditional Korean floor heating system. Under the condition of which the supply of light-weight aggregates are limited, the development of light-weight concrete using air voids is highly required in the aspects of reduced manufacturing prices and mass production. In this study, we investigated the physical properties and thermal behaviors of specimens that applied different mixing ratios of foaming agent to evaluate the possibility of use in the structural elements. We proposed the estimating equation for compressive strength of each mix having different ratio of foaming agent. We also confirmed that the density of cement matrix is decreased as the mixing amount of foaming agent increase up to 0.6% of foaming agent mixing ratio which was observed by SEM. Based on porosity and compressive strength of control mortar without foaming agent, we built the estimating equations of compressive strength for mortars with foaming agent. The upper limit of use in foaming agent is about 0.6% of the binder amount. Each air void is independent, and size of voids range from 50 to $100{\mu}m$.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.397-400
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• 2002

Vapor explosion is one of the most important problems encountered in severe accident management of nuclear power plants. In spite of many efforts, a lot of questions still remain. So, KAERI launched a real experimental program called TROI using $UO_{2}$ and $ZrO_{2}$ to investigate the vapor explosion. Besides TROI tests, a small-scale experiment with molten-tin/water system was performed to quantify the characteristics of vapor explosion and to understand the phenomenology of vapor explosion. A vapor explosion was observed while the amount of air bubble and water temperature were systematically varied The mass and temperature of tin are $50\;g\;and\;150^{\circ}C$, respectively. Water temperature is set to $24^{\circ}C\;and\;50^{\circ}C$. The void fraction of air bubble ranges from $0\;to\;10\;{\%}$. The strength of vapor explosion was measured using dynamic pressure sensors attached in reactor tube wall. as a function of void fraction. In addition, a high speed video filming up to 1,000 flame/sec was taken in order to visually investigate the behavior of the vapor explosion .

• 방사선산업학회지
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• 제8권1호
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• pp.23-27
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• 2014

Industrial single photon emission computed tomography (SPECT) is an useful technique to investigate the dynamic behavior of process flow. In the present study, to evaluate the influence of a void on the performance of industrial SPECT, industrial SPECT with various radioisotope sources and gas holdups was modeled by the Monte Carlo simulation. The results are very encouraging; that is, the void little influences the performance of industrial SPECT, which means that industrial SPECT could be a suitable tool to investigate the dynamic characteristics of the flow in a water-air phase process.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2022년도 추계학술대회
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• pp.570-573
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• 2022

본 논문에서는 신경망 모델을 적용한 몰드변압기의 보이드 결함 크기 판별에 관한 연구를 수행하였다. PCB 기반의 로고우스키 코일형 부분방전 센서를 제작하여 부분방전 신호를 측정하였고, 보이드에 의한 부분방전 결함을 모의하기 위한 PD 전극계를 제작하였다. 또한 보이드는 원통형 모양의 알루미늄 틀을 제작하여 에폭시가 경화되는 과정에서 실린지를 삽입하고 공기를 주입하여 서로다른 직경을 가지는 4개의 시편을 제작하였다. 보이드 결함 크기 판별을 위해 부분방전 전하량, 방전 펄스 수, 위상 분포의 부분방전 특성 파라미터를 추출하여 Labview 기반의 VI (Virtual Instrument)로 역전파 알고리즘을 설계하였다. 실험 결과로부터 제작된 알고리즘은 90%이상의 판별률로 결함의 직경크기를 구분할 수 있었다. 본 연구의 결과는 현장에서 PD 측정 시 몰드변압기의 유지보수 및 절연물 교체의 근거 자료로 활용될 수 있을 것으로 판단된다.

• 한국도로학회:학술대회논문집
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• 한국도로학회 2010년 추계학술대회 논문집
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• pp.221-226
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• 2010