• 대한설비공학회지:설비저널
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• 제14권2호
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• pp.108-117
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• 1985

In this study, a numerical analysis was performed for the natural convection heat transfer in a vertical channel which was consisted of two finite-thickness vertical walls with heat source. The ratio of the thermal conductivity of wall to air played an important role in the analysis. The case for which one side wall has protrusion resistances was also examined. The governing equations for the system was discretized by control volume formulation and solved by SIMPLE method. As the result of this study, it was found that the uniform heat flux boundary condition could be applied when the conductivity ratio was below approximately 50 and the uniform temperature boundary condition could be used when the conductivity rat io was over approximately 15,000. However, when the conductivity ratio was between 50 and 15,000, the thermal conductivity ratio value should be considered for the analysis. It was also found that the existence of protrusion resistance influenced the thermal field up to the distance of 3-4 times of the protrusion length.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.1478-1486
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• 2009

As a conventional line-fitting method, the Bouwer and Rice method has been popularly adopted to estimate the hydraulic conductivity of an aquifer through a slug test. Because a ventical cutoff wall is usually very compressible and features a small wall thickness, the Bouwer and Rice method should be carefully used for the vertical cutoff wall. In addition, a relatively impermeable layer, called a filter cake, formed at the interface between the cutoff wall and the natural soil formation makes it difficult to use the Bouwer and Rice method directly. In order to overcome such limitations, the original Bouwer and Rice method is modified by incorporating the concept of the flow net method. In this modification, the geometry condition of cutoff walls including the filter cake is effectively considered in evaluating the hydraulic conductivity of a vertical cutoff wall.

• Nuclear Engineering and Technology
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• 제49권3호
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• pp.459-465
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• 2017

The goal of this study is to evaluate the effective thermal conductivity and diffusivity of containment walls as heat sinks or passive cooling systems during nuclear power plant (NPP) accidents. Containment walls consist of steel reinforced concrete, steel liners, and tendons, and provide the main thermal resistance of the heat sinks, which varies with the volume fraction and geometric alignment of the rebar and tendons, as well as the temperature and chemical composition. The target geometry for the containment walls of this work is the standard Korean NPP OPR1000. Sample tests and numerical simulations are conducted to verify the correlations for models with different densities of concrete, volume fractions, and alignments of steel. Estimation of the effective thermal conductivity and diffusivity of the containment wall models is proposed. The Maxwell model and modified Rayleigh volume fraction model employed in the present work predict the experiment and finite volume method (FVM) results well. The effective thermal conductivity and diffusivity of the containment walls are summarized as functions of density, temperature, and the volume fraction of steel for the analysis of the NPP accidents.

• 대한기계학회논문집B
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• 제39권5호
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• pp.425-433
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• 2015

본 논문에서는 외부에서 균일한 직류전기장이 인가될 때 점성유체에 자유롭게 잠겨있는 단일 입자가 근처의 비전도성 평면 벽과의 상호작용 때문에 유발되는 2차원 유전영동 운동에 대하여 수치연구를 수행하였다. 특히 입자-유체 경계면에서 불연속적으로 급격히 변화하는 전기전도도를 가진 Maxwell 방정식을 해석하고 전기장을 구한 후 Maxwell 응력텐서를 적분하여 입자에 작용하는 유전영동 힘을 계산하였다. 해석 결과 전기장이 벽과 평행하게 인가될 때 입자는 항상 반발력이 유도되어 벽으로부터 멀어지는 방향으로 유전영동 운동이 발생하였으며, 그 운동특성은 입자와 벽 사이 간격과 입자의 전도도에 따라 크게 달라졌다. 운동 강도는 입자와 유체의 전도도가 서로 같으면 사라지나, 전도도가 서로 다르면 그 차이가 클수록 강도는 증가하였다.

• 한국지반공학회논문집
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• 제25권12호
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• pp.47-55
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• 2009

순간변위시험(Slug test)을 통해 대수층의 투수계수를 구할 때, 시험결과 해석에 적용하는 line-fitting법 중 가장 일반적인 방법이 Bouwer and Rice법이다. Bouwer and Rice법을 적용하여 압축성이 크고 벽체의 두께가 얇은 연직차수벽의 투수계수를 산정할 때는 세심한 주의가 필요하다. 그리고 연직 차수벽과 주변 지반 사이에 형성된 상대적으로 투수성이 낮은 영역, 즉 필터케이크(Filter cake)는 Bouwer and Rice법을 연직차수벽의 투수계수 산정시, 이 방법을 직접적용하기 어렵게 만든다. 본 논문에서는 기존의 Bouwer and Rice법의 한계를 극복하기 위해서 유선망 개념을 도입한 수정 Bouwer and Rice법을 제안하였다. 수정된 Bouwer and Rice법은 연직차수벽의 투수계수를 산정할 때 필터케이크를 포함한 연직차수벽의 기하학적 조건을 효율적으로 반영할 수 있도록 한다. 또한, 수정 Bouwer and Rice법의 적용성을 검증하기 위한 사례 연구가 본 논문에서 수행되었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회
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• pp.1264-1273
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• 2010

Soil-bentonite cutoff walls are widely recognized to be the effective barrier for containment of wastes and groundwater. Bentonite cake is usually found remaining on the trench surface due to the use of bentonite slurry during the excavation for the cutoff wall construction. Defects also inevitably take place due to the inappropriate construction procedures or improperly mixed soil-bentonite backfill. The defects include insufficient keys and windows in the soilbentonite cutoff wall. In this study, the performance of the soil-bentonite cutoff wall is evaluated based on the flow rates through the wall. Three-dimensional numerical models were applied to simulate the groundwater flow through the soil-bentonite cutoff walls of typical geometries with consideration of the defects and bentonite cake. Results of the simulations showed that the bentonite cake has no effect in the insufficient key cases. In the keyed wall cases, the bentonite cake with very low hydraulic conductivity significantly impedes the flow of groundwater through the wall. The presence of the bentonite cake not only compromises the window defect but also renders the wall construction more effective in blocking the groundwater flow. These findings show the significance of the bentonite cake in a soil-bentonite cutoff wall construction.

• 한국가시화정보학회지
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• 제21권3호
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• pp.33-38
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• 2023

Spray cooling is a method of cooling high-temperature heating elements by spraying droplets. Recently, spray cooling has been proposed for use in next-generation nuclear reactors. When droplets are sprayed onto the outer wall of a heat exchanger tube, a film boiling occurs on the outer wall. Over time, the outer wall temperature decreases, and a liquid film forms on the outer wall, and the heat exchanger outer wall is subsequently cooled by the liquid film. In this case, the liquid film thickness has a great influence on the heat removal performance. In this study, an experimental study was conducted to measure the liquid film thickness distribution in a droplet spray environment. For this purpose, a method using the electrical conductivity of the liquid was adopted.

• 한국화재소방학회논문지
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• 제32권2호
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• pp.17-23
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• 2018

본 연구에서는 Buckingham 파이 정리를 이용하여 구획 공간에서 화재가 발생한 경우 벽면을 구성하는 재료의 열전도 계수와 내부 온도의 상관관계에 관한 연구를 수행하였다. 이를 위해서 기존 무차원 변수의 주요 인자를 고려하여 발열량, 열전도계수, 구획공간의 체적, 벽면 두께 그리고 대류 열전달 계수의 관계를 분석하였다. 또한, 발열량에 대한 화염에서의 최대 온도 그리고 벽면의 온도를 산출하기 위해서 내화보드를 사용하여 ISO 9705 룸 코너 시험기(Room Corner Tester)의 1/6 크기를 갖는 축소 규모의 구조물을 제작하였으며, 10 cm, 15 cm 그리고 20 cm인 정사각형 화원에 대해서 가솔린 화재실험을 수행하여 국부 지점의 산소 농도와 화염에서의 온도분포를 측정하였다. 그 결과 대류 열전달 계수와 열전도 계수의 변화에 따라서 외벽에서의 온도가 증가하는 조건을 제시하였으며, 발열량 변화에 대한 Buckingham 파이의 무차원 경험식을 도출하였다. 본 연구 결과는 구획 공간에서 외벽 형상 및 열전도 계수의 변화를 고려한 화재 현상을 연구하기 위한 기초 자료의 활용이 가능할 것으로 사료된다.

• 대한기계학회논문집B
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• 제21권6호
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• pp.773-778
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• 1997

The present study investigates the effect of the shear rate-dependent thermal conductivity of non-newtonian fluids on the heat transfer enhancement in a 2:1 rectangular duct flow. An axially-constant heat flux and a peripherally-constant temperature boundary conditions(H1) was adopted for a top-wall-heated configuration. The present numerical results of Nusselt numbers for SRDC(Separan) show heat transfer enhancement over those of SRIC. The Nusselt numbers increased linearly as Reynolds numbers increased. The heat transfer enhancement is due to an increased thermal conductivity near the wall, which is attributed to the shear rate-dependence.

• 한국재료학회지
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• 제31권8호
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• pp.450-457
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• 2021

From measured thermal conductivity and modeling by simulation, this study suggests that U-factors are highly related to materials used between steel and polymer. The objective and prospective point of this study are to relate the relationship between the U-factor and the thermal conductivity of the materials used. For the characterization, EDX, SEM, a thermal conductive meter, and computer simulation utility are used to analyze the elemental, surface structural properties, and U-factor with a simulation of the used material between steel and polymer. This study set out to divide the curtain wall system that makes up the envelope into an aluminum frame section and entrance frame section and interpret their thermal performance with U-factors. Based on the U-factor thermal analysis results, the target curtain wall system is divided into fix and vent types. The glass is 24 mm double glazing (6 mm common glass +12 mm Argon +6 mm Low E). The same U-factor of 1.45 W/m²·K is applied. The interpretation results show that the U-factor and total U-value of the aluminum frame section are 1.449 and 2.343 W/m²·K, respectively. Meanwhile, those of the entrance frame section are 1.449 and 2.