• Journal of the Korean Society of Visualization
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• v.17 no.1
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• pp.60-68
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• 2019

Flow visualizations have been carried out to analyze the characteristics of bubby flows exhausted from a venturi-type bubble generator with an air vent. For various design parameters and operating conditions of the bubble generator, the images of bubbly flows was recorded using a high-speed camera and a microscope. Then the amount and size distribution of bubble was evaluated by an image processing technique. The results show that for increasing the amount of bubble, it is more effective to reduce the venturi throat than to enlarge the air vent diameter. If the water flow rate increases, the bubble generation rate increases but reaches a status of saturation, whose condition depends on Reynolds number at a given air vent diameter. The bubble size increases as the diameter of venturi throat decreases and Reynolds number increases. However, the air vent diameter is not a significant factor on bubble size.

• Journal of the Korea Institute of Building Construction
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• v.15 no.4
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• pp.383-389
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• 2015

The objective of this study is to develop mixture proportioning approach of crack controlled lightweight foamed concrete without using high-pressure steam curing processes, as an alternative to autoclaved lightweight concrete blocks (class 0.6 specified in KS). To control thermal cracks owing to hydration heat of cementitious materials, 30% ground granulated blast-furnace slag (GGBS) was used as a partial replacement of ordinary portland cement (OPC). Furthermore, polyvinyl alcohol (PVA) and polyamid (PA) fibers were added to improve the crack resistance of foamed concrete. The use of 30% GGBS reduced the peak value of hydration production rate measured from isothermal tests by 28% and the peak temperature of foamed concrete measured from semi-adiabatic hydration tests by 9%. Considering the compressive strength development, internal void structure, and flexural strength of the lightweight foamed concrete, the optimum addition amount of PVA or PA fibers could be recommended to be $0.6kg/m^3$, although PA fiber slightly preferred to PVA fiber in enhancing the flexural strength of foamed concrete.

• The Journal of the Acoustical Society of Korea
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• v.28 no.1
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• pp.10-18
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• 2009

A moving surface vessel generates a ship wake which contains a cloud of micro-bubbles with radii ranging between $8{\sim}200{\mu}m$. Such micro-bubbles can be detected by active sonar system for more than ten minutes depending on the size and speed of the surface vessel. In this paper, a reverberation model for the ship wake is presented. The developed model consists of the acoustic scattering model due to the distribution of the micro-bubbles and the kinematic model for the moving active sonar. The acoustic scattering model is based on the volume integration, where the volume scattering strengths are obtained from the spatial distribution of micro-bubbles. Since the directivity and look-direction of active sonar are important factors for moving active sonar, the kinematic model utilizes the Euler transformation to obtain the relative motion between the global and local coordinates. In order to verify the developed model, a series of sea experiment was executed in September 2007 to obtain the spatial-temporal distribution of a bubble cloud, and analyzed to be compared with the simulation results.

• Journal of Korea Water Resources Association
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• v.41 no.7
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• pp.669-679
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• 2008

The present study examines similarity of behavior between an overtopping wave generated by a plunging wave and a dam-break flow through hydraulic model tests. The dam-break flow has been employed to estimate the overtopping effect on the basis of the dam-break flow's behavior similar to the overtopping. In this study, the overtopping velocity was measured by a modified image technique using bubble and bubble texture images called bubble image velocitmetry. From the measurements, the vertical profiles of horizontal overtopping velocity at cross-sections along the deck were presented and discussed. Maximum velocity and depth-averaged velocity at each cross-section were compared with an analytical solution solving the dam-break flow, Ritter's solution. The initial water depth of importance for the solution was determined from the tested wave condition and the overtopping measurements. The comparison shows that the solution with the initial water depth estimated using the front velocity of the overtopping wave is in good agreements with the measurements.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2008.04a
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• pp.69-75
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• 2008

기포반응도는 월성발전소를 비롯한 CANDU형 원자로의 주된 안전성 쟁점사안으로 끊임없이 논의되어 왔다. 이는 설계기준사고가 노심에서 열에너지 불균형이 원인이 되어 기준이상의 핵연료 파손과 방사성물질 누출로 발전할 위험이 있는 사건들로 정의될 때, 사건 진행 과정에 기포반응도 증가는 조기에 운전중단을 실패할 경우 출력폭주로 이어지므로 사건의 결말이 중대사고로 전환될 위험이 크기 때문이다. 본 연구는 공개된 최신 핵자료인 ENDF/B-VII.0를 NJOY.99로 처리한 연속에너지 반응단면적 라이브러리를 구축하고 MCNP-4C에 접속하여 37봉 천연우라늄 핵연료다발의 표준노심격자에 대한 기포반응도를 시뮬레이션하여, 지금까지 각종문헌에 제시된 값들과 비교, 종합하므로 내제된 불확실성을 추정하는 내용이다. ENDF/B-VII.0 기반 MCNP-4C의 CANDU 노심격자 모델은 동일한 핵자료와 핵종농도를 사용한 WIMS-IAEA 모델과 비교할 때, 초기 노심의 임계도 오차 약 3.51mk가 연소 진행에 따라 $7.5\times10^{-4}mk$/MWD/teU의 비율로 감소하는 것으로 나타났다. 또한 MCNP-4C 예측기포반응도는 초기노심에서 기포율 50% 및 100%에 대해 각각 8.38 및 15.96mk, 평형노심에서 7.68 및 14.72mk로 계산된다. 이는 월성 2, 3, 4 FSAR의 초기노심 및 평형노심에서 100% 기포상태에 대한 값, 약15.0 및 10.6mk와 비교할 때, 초기노심은 약 1.0mk 평형노심은 약4, 1mk 보수적이지만, 다른 연구결과들과는 최대오차 ${\pm}1{\sim}2mk$ 이내에서 잘 일치하는 것으로 평가되었다. 본 연구는 CANDU 노심의 기포반응도 불확실성 요인의 규명 및 영향평가를 위한 노력의 일부로서 앞으로 감속재의 붕산농도 변화, 감속재 및 냉각재의 중수 순도 변화, 기기노화에 의한 격자 구조 및 물성 변화, 중성자속 및 출력 분포 불균형, 반응도조절장치의 위치, 등 주요 설계변수의 변화에 대한 반응도영향 분석연구를 계속할 계획이다.

• Journal of IKEEE
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• v.16 no.3
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• pp.211-216
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• 2012

In the phase boundary estimation problem, the estimation performance depends on the initial guess. However, there is no information on the number of bubbles and those positions for the initial guess in real flows. Therefore, it is very important to set appropriate initial guesses from prior information. In this paper, in order to set initial guesses for estimating the phase boundaries in two-phase flows, first, unknown resistivity distribution was estimated using the difference reconstruction method. After that, an adaptive threshold value was automatically computed using intermodes method. Based on this value, the number of bubbles and the initial position were determined. The numerical experiments have been performed to evaluate the estimation performance of the proposed method.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.197-197
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• 2003

현재 PDP(Plasma Display Panel) 투명유전체층은 PbO 계열을 사용하고 있으나 제조공정 시 다량의 중금속 페기물이 방출됨에 따라 환경오염을 야기시킴으로 무연조성이며 저온소성이 가능한 저융점유리인 인산염계 유리에 대한 열적, 화학적, 광학적 특성에 대해 체계적인 연구가 진행되었다. 광학적 특성을 위 한 승온속도, 소성온도, 유지시간의 변화 그리고, 프릿 입도에 따른 광 투광성, 기포의 형성, 그리고 기포의 분포특성을 연구하였다. 열적특성은 DTA와 TMA를 이용하여 유리전이점(Tg) 및 선팽창계수(CTE)와 Littleton softning point (Ts)가 측정되었다. 광학적특성은 스크린프린팅법으로 후막 제조 후 소성하여 UV-visible spectrometer을 이용하여 300~800nm영역에서 투광성을 측정하였으며, FEG-SEM, AFM을 이용해 표면을 관찰하였다. 결과로써, Tg는 440-46$0^{\circ}C$ 와 CTE는 7~8.5$\times$$10^{-6}$K값을 보였고 높은 화학적 내구성과 60-80%의 광투과율을 나타내었다. 프릿의 미세화, 숭온속도의 감소는 기포의 생성을 줄이는데 효과를 보였으며, 그 결과 양호한 광투과율을 얻을 수 있었다. 이러한 결과에 따르면, P$_2$O$_{5}$-ZnO-RO 조성은 PDP용 투명유전체 조성으로써 기존의 PbO계열을 대체할만한 새로운 조성으로 고려된다.

• Journal of Energy Engineering
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• v.4 no.3
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• pp.420-428
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• 1995

현재 사용하고 있는 액화천연가스 기화기는 관내부로 -162$^{\circ}C$의 액화가스가 흐르고, 관외부로 발전소 증기응축기 출구에서 배출된 20~3$0^{\circ}C$의 해수를 흐르도록 하여, 두 유체사이의 온도차로 기화시키는 간접접촉방식 열교환기가 사용되고 있다. 그러나 간접접촉방식 열교환기는 두 유체사이의 큰 온도차로 인한 금속재료의 피로현상과 해수의 염분에 의한 재질의 부식 및 미생물 부착 등의 원인으로 열전달효율이 저하되고 있다. 따라서 본 연구는 관을 중간매체로 하는 간접접촉식 열교환기대신 액화천연가스와 기화용수인 물을 직접접촉시키는 방법으로 이용하여, 위와 같은 문제점들을 근본적으로 해결하려 한다. 본 실험에서는 기화기내의 수위 500 mm와 물의 유량 10 l/min을 일정하게 고정시키고, 액화천연가스의 유량 0.12 ㅣ/min, 0.36 l/min, 0.6 l/min, 기화기내의 압력을 100 kPa, 300 kPa, 500kPa로 변화시키면서 기화기내의 기포, 온도분포, 급팽창현상, 동결현상 및 기화후 수분함유량등의 비등특성을 규명하였다. 실험결과 기화기내의 압력이 증가할수록 기포는 작고 균일한 분포를 이루고, 폭발적인 급팽창현상은 일어나지 않았다. 또한 동결현상은 액화천연가스의 기화를 방지하지 못하였으며, 기화된 천연가스내의 수분함유량 몰%는 압력과 유량이 증가함에 따라 감소하는 경향을 보이고 있다.

• Journal of Chest Surgery
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• v.29 no.4
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• pp.408-413
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• 1996

In most cases of diffuse bullous emphysema and chronic obstructive lung disease, t e risk of surgical treatment is very high. But surgical treatment in selected cases of bullous emphysema with localized involvement of only one side of the lung has suggested safe and good management. So patient selection of surgical treatment Is one of the most important things in management of bullous emphysema. From 1987 to 1992, 11 patients were operated for bullous emphysema with giant bullae at the Department of Thoracic and Cardiovascular Surgery of Chonbuk National University Hospital. Author selected surgical candidates who had progressive dyspnea and symptomatic bullae occupying more than one third of the hemithorax and shifting the trachea and mediastinum to the opposite side of the lung. There were 7 males and 4 females ranged from 19 to 61 years of age. Operative procedures were bullectomy and/or wedge resection in 7 cases, segmentectomy in 2 cases and lobectomy in 2 cases. Symptoms and pulmonary function of all patients were improved six months to three years postoperat vely. There were no postoperative death. We conclude that surgical treatment of bullous emphysema with giant bullae is safe and a good treatment of modality in indicated patients.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.85-92
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• 2016

The eight mixes and artificial soil aggregates were prepared for evaluating the practical application of lightweight foamed concrete as soil aggregates. The main parameter was unit binder content ranged between from 100 to $800kg/m^3$. In lightweight foamed concrete, flow, slurry and dried density, and compressive strength at different ages were measured. In Artificial soil aggregates crushed from lightweight foamed concrete, particle size distribution, pH, coefficient of permeability, cation exchange capacity(CEC), and ratio of carbon to nitrogen(ratio of C/N), were measured. The test results showed that flow, slurry and dried density, and compressive strength at different ages of lightweight foamed concrete increased with the increasing of unit binder content. Compressive strength at age of 28, of lightweight foamed concrete with unit binder of more than $500kg/m^3$, was more than 4 MPa. The ammonium phosphate immersion time of more than age of 3, was effective to decrease pH of artificial soil aggregates. In addition, artificial soil aggregates was evaluated as high class in terms of cation exchange capacity(CEC), while satisfied with value of ratio of carbon to nitrogen(ratio of C/N) recommended by landscape specification.