• Corrosion Science and Technology
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• 제19권3호
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• pp.122-130
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• 2020

In this study, a corrosion failure analysis of a heat transport pipe was conducted, as the result of a pinhole leak. Interestingly, the corrosion damage occurred externally in the pipeline, resulting in severe thickness reduction near the seam line. Also, while a stable magnetite protective film formed on the inner surface, the manganese oxide formation occurred only on the outer surface. The interior and exterior of the pipe were composed of ferrite and pearlite. The large manganese sulfide and alumina inclusions were found near the seam line. In addition, the manganese sulfide inclusions resulted in grooving corrosion, which progressed in the seam line leading to the reduction in the thickness, followed by the exposure of the alumina in the matrix to the outer surface. To note, the corrosion was accelerated by pits generated from the boundaries separating the inclusions from the matrix, which resulted in pinhole leaks and water loss.

• Corrosion Science and Technology
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• 제19권4호
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• pp.189-195
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• 2020

Two air vents situated on a heat transport pipe in district heating system were exposed to the same environment for 10 years. However, one air vent was more corroded than the other. It also had a hole on the top of the front-end pipe. Comparative analysis was performed for these air vents to identify the cause of corrosion and establish countermeasures. Through experimental observation of the damaged part and analyses of powders sampled from air vents, it was found that corrosion was initiated at the top of the front-end pipe. It then spread to the bottom. Energy dispersive X-ray spectroscopy results showed that potassium and chlorine were measured from the corroded product in the damaged air vent derived from rainwater and insulation, respectively. The temperature of the damaged air vent was maintained at 75 ~ 120 ℃ by heating water. Rainwater-soaked insulation around the front-end pipe had been hydrolyzed. Therefore, the damaged air vent was exposed to an environment in which corrosion under insulation could be facilitated. In addition, ion chromatography and inductively coupled plasma measurements indicated that the matrix of the damaged front-end pipe contained a higher manganese content which might have promoted corrosion under insulation.

• 한국해안해양공학회지
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• 제6권3호
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• pp.245-259
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• 1994

연직 확산계수의 산정에 k-I 난류방정식을 도입하여 예측성을 향상시킨 치안 해수유동 및 온배수 확산에 관한 3차원 수치모형을 개발하였다. 모형은 1차원 수로에서 취송류의 연직분포, 정지수역으로의 온배수 젯트에 대하여 수리실험자료와의 비교검증을 실시하고 고리해역에서 조류 및 온배수 확산을 해석하여 현장 적용성을 검토하였다. 계산결과는 검증에 사용된 자료와 대체로 일치하는 양호한 결과를 보였으며, 취송류, 밀도류, 조류에 대하여 동일한 모형상수를 사용하여 연직 확산계수를 계산할 수 있어 난류모형의 상수가 보편성이 있음을 확인하였다. 따라서, 본 연구에서 $textsc{k}$-ι 난류방정식을 도입하여 개발된 수치모형은 연안 해수유동을 대표하는 취송류, 밀도류, 조류에 대하여 난류상수의 보편성과 모형의 예측성을 갖고 있어 연안 해수유동 및 확산을 연구하는 데 효율적으로 활용될 수 있을 것으로 사료된다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
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• pp.178-181
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• 2008

Cylindrical stainless-steel/sodium heat pipe for a high-temperature application was manufactured and tested for transient and steady-state operations. The container material was made of stainless-steel 316, and the working fluid was sodium. Stainless-steel 316 mesh screen was inserted as a capillary structure. The working fluid fill charge ratio was approximately 64 $\sim$ 181% based on the pore space of the wick. The outer diameter of the heat pipe was 12.7 mm and the total length was 250 mm. The evaporator part was 150 mm and the condenser 80 mm. The performance test of the heat pipe has been conducted in the furnace with up to 800 W. The variation of the average heat transfer coefficient was investigated as a function of heat flux and vapor temperature. As input thermal load increased, it was showed that difference of temperatures in evaporator and condenser decreased and that operating section and heat transfer characteristics at the heat pipe increased.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.315-316
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• 2006

The paper presents some results regarding the obtaining of some copper heat pipes with a porous copper internal layer for electronic components cooling. The heat pipes were realized by sintering of spherical copper powders of $90{\div}125\;{\mu}m$ size directly on the internal side of a copper pipe of 18 mm in diameter. The obtained pipes were then brazed in order to obtain a heat pipe of 0.5 m in length. After that, the heat pipe was sealed and filled with a small quantity of distilled water as working fluid. To establish the total heat transport coefficient and the thermal flow transferred at the evaporator, some external devices were realized to allow the heating of the evaporator and the cooling of the condenser. Water heat pipes are explored in the intermediate temperature range of 303 up to 500 K. Test data are reported for copper water heat pipe, which was tested under different orientations. The obtained results show that the water heat pipe has a good thermal transfer performance in the temperatures range between 345 and 463 K.

• 교육녹색환경연구
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• 제4권4호
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• pp.19-24
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• 2004

The thermal effect of a transparent insulated opake wall with solar energy was investigated theoretically. The heat gain through transparent insulated opake wall was studied for relative simple conditions. The stationary heat transport effect was studied for layer which is built on the opake wall. This study shows that a relative low solar radiation intensity causes a great heat reduction through the transparent insulated opake wall. Because the transparent insulation layer is mostly transparent to solar radiation, it is opaque to heat radiation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.360-364
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• 2001

Numerical Aanlysis is made on the thermal performance of micro heat pipe in a axial flat grooved channel. The flow of liquid and vapor is investigated in trapezoidal grooves and the effect of variable shear stress along the interface of the liquid and vapor considered. The results from this study are obtained in the axial variation of pressure difference between vapor and liquid, contact angle, velocity of liquid and vapor and so forth. In addition, maximum heat transport capacity of micro-heat pipe is provided by varying the operation temperature, and compared with that from Schneider and Devos's model in which the interfacial shear stress is neglected.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.524-529
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• 2001

Because of the ozone layer depletion and global wanning, new alternative refrigerants are being developed. Among them, HFC refrigerants are thought promising, but some European countries are arguing that these refrigerants are also harmful to the global wanning. Therefore, natural refrigerants should be considered as an eventual alternative in refrigerators and heat pumps. In the present study, the supercritical gas cooling process are computationally analysed by employing various turbulence models of carbon dioxide in a trans critical refrigeration cycle. The gas cooling process near the critical point experiences a drastic change in thermodynamic and transport properties, thus the heat transfer characteristics would be different from those of two or single phases. Based on the computational results, the correlations to estimate the near-critical heat transfer characteristics will are obtained.

• 대한기계학회논문집B
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• 제30권7호
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• pp.700-706
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• 2006

This study presents a numerical procedure to optimize the shape of dimple surface to enhance turbulent heat transfer in a rectangular channel. The response surface based optimization method is used as an optimization technique with Reynolds-averaged Wavier-Stokes analysis of fluid flow and heat transfer with shear stress transport (SST) turbulence model. The dimple depth-to-dimple print diameter ratio, channel height-to-dimple print diameter ratio, and dimple print diameter-to-pitch ratio are chosen as design variables. The objective function is defined as a linear combination of heat transfer related term and friction loss related term with a weighting factor. full factorial method is used to determine the training points as a mean of design of experiment. The optimum shape shows remarkable performance in comparison with a reference shape.

• 대한기계학회논문집
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• 제6권4호
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• pp.331-340
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• 1982

Numerical analysis is made on the turbulent heat transfer with suspension of solid particles in circular tube with constant heat flux. The mean motion of suspending particles in mixture is treated as the secondary gas flow with virtual density and viscosity. Our modeling of turbulent transport phenomena of suspension flow is based on this assumption and conventional mixing length theory. This paper gives the evidence that the mixing length models can be extended to close the governing equations for two phase turbulent flow with solid boundary at a first order level. Results on Nusselt numbers obtained by analytical treatments are compared with available experimental data and discussed. They suggest that the most important parameters of two phase turbulent heat transfer phenomena are relative particle diameter to pipe diameter, gas-solid loading ratio, and specific heat of suspending material.