• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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• pp.550-554
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• 2007

A one-dimensional heat transfer model coupled with parameter estimation is developed in this study to predict the effective thermal conductivities of soil formation and borehole resistances from in situ field test data. In this application a new method of using initial ignoring time(IIT) obtained from error estimation is tried and turned out to be successful in determining soil thermal conductivities. The validity of this model is accomplished through comparison of the predicted temperature profiles of the model with the data from laboratory scale experimental setting. Eleven test boreholes were constructed in Ochang, Chungcheong Buk Do, and thermal response test was carried out with each borehole. The results of the in situ tests were analyzed with our 1-D numerical model and compared with the results of line source method. The comparison shows that the thermal properties from line source method is a little lower (${\sim}95%$)than those from numerical method. The reason of such result seems to be the lower thermal conductivity of grout material, which is not counted in line source method.

• Journal of Advanced Marine Engineering and Technology
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• 제38권10호
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• pp.1200-1205
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• 2014

The effect of nanofluids on the heat transfer performance of a pulsating heat pipe has been experimentally investigated. Water-based diamond nanofluid and aluminium oxide ($Al_2O_3$) nanofluid were tested in the concentration range of 0.5-5%. The pulsating heat pipe was constructed using clear Pyrex tubes of 1.85 mm in inner diameter in order to visualize the pulsating action. The total number of turns was eight each for heated and cooled parts. The supply temperatures of heating water and cooling water were fixed at $80^{\circ}C$ and $25^{\circ}C$ respectively. The liquid charging ratio of the nanofluid was 50-70%. The test results showed that the case of 5% concentration of diamond nanofluid showed 18% increase in heat transfer rate compared to pure water. The case of 0.5% concentration of $Al_2O_3$ nanofluid showed 24% increase in heat transfer rate compared to pure water. But the increase of $Al_2O_3$ nanofluid concentration up to 3% did not show further enhancement in heat transfer. It is also observed that the deposited nanoparticles on the tube wall played a major role in enhanced evaporation of working fluid and this could be the reason for the enhancement of heat transfer by a nanofluid, not the enhanced thermal conductivity of the nanofluid.

• Journal of Advanced Marine Engineering and Technology
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• 제39권8호
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• pp.801-806
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• 2015

The experimental analysis of a crevice-type vapor chamber heat pipe (CVCHP) is investigated. The heat source of the CVCHP is a high-power light-emitting diode (LED). The CVCHP, which exhibits a bubble pumping effect, is used for heat dissipation in a high-heat-flux system. The working fluid is R-141b, and its charging ratio was set at 60 vol.% of the vapor chamber in a heat pipe. The total thermal conductivity of the falling-liquid-film-type model, which was a modified model, was 24% larger than that of the conventional model in the LED package. Flow visualization results indicated that bubbles grew larger as they combined. These combined bubbles pushed the working fluid to the top, partially wetting the heat-transfer area. The thermal resistance between the vapor chamber and tube in the modified design decreased by approximately 32%. The overall results demonstrated the better heat dissipation upon cooling of the high-power LED package.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.148-148
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• 2017

Surface modification is a type of mechanical manipulation skills to achieve extensive aims including corrosion control, exterior appearance, abrasion resistance, electrical insulation and electrical conductivity of substrate materials by generating a protective surface using electrical, physical and chemical treatment on the surface of parts made from metallic materials. Such surface modification includes plating, anodizing, chemical conversion treatment, painting, lining, coating and surface hardening; this study conducted cavitation experiment to assess improvement of durability using anodizing. In order to observe surface characteristics with applied current density, the electrolyte temperature, concentration was maintained at constant condition. To prevent hindrance of stable growth of oxide layer due to local temperature increase during the experiment, stirring was maintained at constant speed. In addition, using galvanostatic method, it was maintained at processing time of 40minutes for 10 to $30mA/cm^2$. The cavitation experiment was carried out with an ultra sonic vibratory apparatus using piezo-electric effect with modified ASTM-G32. The peak-to-peak amplitude was $30{\mu}m$ and the distance between the horn tip and specimen was 1mm. The specimen after the experiment was cleaned in an ultrasonic bath, dried in a vacuum oven for more than 24 hours, and weighed with an electric balance. The surface damage morphology was observed with 3D analysis microscope. As a result of the study, differences were observed surface hardness and anti-cavitation characteristics depending on the development of oxide film with the anodizing process time.

• 한국정밀공학회지
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• 제34권4호
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• pp.247-251
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• 2017

Titanium alloy has been widely used in the aerospace industry because of its high strength and good corrosion resistance. During cutting, the low thermal conductivity and high chemical reactivity of titanium generate a high cutting temperature and accelerates tool wear. To improve cutting tool life, cryogenic machining by using a liquid nitrogen (LN2) jet is suggested. In cryogenic jet cooling, evaporation of LN2 in the tank and transfer tube could cause pressure fluctuation and change the cooling rate. In this work, cooling uniformity is investigated in terms of liquid nitrogen jet pressure in cryogenic jet cooling during titanium alloy turning. Fluctuation of jet spraying pressure causes tool temperature to fluctuate. It is possible to suppress the fluctuation of the jet pressure and improve cooling by using a phase separator. Measuring tool temperature shows that consistent LN2 jet pressure improves cryogenic cooling uniformity.

• Nuclear Engineering and Technology
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• 제31권1호
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• pp.29-48
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• 1999

Local two-phase flow parameters of subcooled flow boiling in inclined annulus were measured to investigate the effect of inclination on the internal flow structure. Two-conductivity probe technique was applied to measure local gas phasic parameters, including void fraction, vapor bubble frequency, chord length, vapor bubble velocity and interfacial area concentration. Local liquid velocity was measured by Pilot tube. Experiments were conducted for three angles of inclination; 0$^{\circ}$(vertical), 30$^{\circ}$, 60$^{\circ}$. The system pressure was maintained at atmospheric pressure. The range of average void fraction was up to 10% and the average liquid superficial velocities were less than 1.3 m/sec. The results of experiments showed that the distributions of two-phase How parameters were influenced by the angle of channel inclination. Especially, the void fraction and chord length distributions were strongly affected by the increase of inclination angle, and flow pattern transition to slug flow was observed depending on the How conditions. The profiles of vapor velocity, liquid velocity and interfacial area concentration were found to be affected by the non-symmetric bubble size distribution in inclined channel. Using the measured distributions of local phasic parameters, an analysis for predicting average void fraction was performed based on the drift flux model and flowing volumetric concentration. And it was demonstrated that the average void fraction can be more appropriately presented in terms of flowing volumetric concentration.

• Journal of Advanced Marine Engineering and Technology
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• 제31권4호
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• pp.363-369
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• 2007

Probably the most significant heat transfer in the cryogenic liquid hydrogen storage tank from the atmosphere may occur through its support system. In this paper the efficient support system for the cryogenic storage vessel was newly developed and analysed. The support system was composed of a spherical ball as a supporter to reduce the contact area. which is located between two supporting SUS tubes inserted SUS and PTFE blocks. Numerical analyses for temperature distribution, and the thermal stress and strain of the support system were performed by the commercial codes FLUENT and ANSYS. The heat transfer rate of the supporter was evaluated by the thermal boundary potential method which can consider the variation of thermal conductivity with temperature. The results showed that the heat transfer rate through the developed supporter compared with the common SUS tube supporter was significantly reduced. The thermal stress and strain were obtained well below the limited values. It was found that the developed supporter can be one of the most efficient support systems for cryogenic liquid storage vessel.

• 설비공학논문집
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• 제24권7호
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• pp.545-552
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• 2012

The objective of this study is to analyze the effect on the energy consumption of an instant cooling type water purifier by the design parameters of the cooling tank. Initially, the simulation program was developed and verified. The simulation results showed that the energy consumption was reduced by replacing the shape of the cooling tank from a rectangular to a cube, increasing the evaporator length, decreasing the volume of the cooling tank, and increasing the performance of the insulator. The order of the effect magnitude on the energy consumption was as follows; volume of the cooling tank, conductivity and thickness of the insulator, shape of the cooling tank, length of the evaporator, and length of the water tube.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.517-520
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• 2004

Concrete Filled steel Tube pipe structure is a rational type of structure that maximizes performance by combining the strong points of steel frame and concrete. In the structure, the confining effect of steel pipes increases the bearing power of infilled concrete and the strengthening of local bucking of steel pipes by infilled concrete increases the bearing power of members. and these result in the reduction of cross-sectional area and high transformation capacity. Moreover. the structure is economically efficient and widely applicable that it is used from super-high buildings to residential, business and apartment buildings. It enables the construction of multi-story buildings with long spans using columns of small cross-sectional area. In case of diaphragm, however, it is difficult to confirm the compactness of the closed inside of steel pipes. The present study examined the properties of super-high strength concrete over 80MPa by comparing it with 40MPa concrete through heat conductivity and length change tests based on a mixture ratio satisfying the mixture goal presented in the guideline for the design and construction of concrete-filled steel pipe structure. and evaluated the performance of super-high strength concrete according to the shape and size of the aperture ratio of diaphragm.

• 산업융합연구
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• 제20권10호
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• pp.33-38
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• 2022

본 논문에서는 용액 기반의 탄소나노튜브(CNT: Carbon Nano-tube)를 전자기기의 전도성 소재로 사용하기 위하여 쉽고 빠르게 형성하는 방법에 대해 연구하였다. 이를 위해 스핀 코팅 방법 및 아르곤 상압플라즈마 공정을 적용하여 글라스 위에 CNT 박막 코팅을 진행하였다. 코팅 횟수에 따른 전기적, 물리적 특성 변화를 관찰하기 위하여 1회부터 5회까지 동일한 방법으로 형성된 샘플을 제작하였고, 각 샘플에 대해 표면 형상, 반사도, 투과도, 흡수율 및 표면 저항을 측정하였다. 현미경을 이용하여 관찰했을 때 횟수가 늘어날 때 글라스 상에 검은 형상이 더 잘 관찰되며, 특히 스핀코팅에 의해 가운데 영역이 더 검게 관찰되는 것을 알 수 있다. 코팅 수가 증가함에 따라 측정 파장의 전 영역에서 투과도는 감소, 반사도 및 흡수율은 증가하였다. 또한, 파장이 감소함에 따라 투과율은 감소, 반사도 및 흡수율은 증가한다. 전기적인 특성의 경우, 2번 코팅했을 때 전도도가 상당히 향상됨을 확인할 수 있었으며, 추가 코팅에 의해서 전도도 감소가 관찰되지만, 큰 변화를 보이지는 않았다. 결론적으로 CNT를 투명전극으로 대체하기 위해서는 반사도 및 전기전도도를 함께 고려하여 코팅 횟수를 고려해야 하며, 2회가 최적임을 알 수 있다.