• KIEAE Journal
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• 제16권6호
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• pp.159-166
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• 2016

Purpose: The architectural structures in the engineering field include more than one material, and the heat transfer through these multiple materials becomes complicated. More or less, the analytic solutions obtained by the hand calculation can provide the limited information of heat transfer phenomena. However, the engineers have generally been forced to obtain reliable results than those of the hand calculation. The numerical calculation such as a finite volume methods with the unstructured grid system is only the suitable means of the analysis for the complex and arbitrary domains that consists of multiple materials. In this study, a new numerical code is developed to provide temperature distributions in the multiple material domains, and the results of this code are compared with the validation cases in ISO10211. Method: Finite volume methods with an unstructured grid is employed. In terms of numerical methods, the heat transfer conduction coefficient is not defined on the surface of the cell between different material cells. The heat transfer coefficient is properly defined to accurately mimic the heat transfer through the surface. The boundary conditions of heat flux considering radiation or heat convection are also developed. Result: The comparison between numerical results and ISO 10211 cases. We are confirmed that the numerical method provides the proper temperature distributions, and the heat transfer equation and its boundary conditions are developed properly.

• Journal of Advanced Marine Engineering and Technology
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• 제28권3호
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• pp.500-508
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• 2004

The heat transfer coefficients during gas cooling process of carbon dioxide in a horizontal tube were investigated. The experiments are conducted without oil in the refrigerant loop. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater, and a gas cooler(test section). The water loop consists of a variable-speed pump, an isothermal tank, and a flow meter. The gas cooler is a counterflow heat exchanger by cooled water flowing in the annulus. The $CO_2$ flows in the horizontal stainless steel tube. which is 9.53mm in O.D. and 7.75mm in I.D. The gas cooler is 6 [m] in length. which is divided into 12 subsections, respectively. The experimental conditions considered in the study are following range of variables : refrigerant temperature is between 20 and $100^{\circ}C$. mass fluxes ranged from 200 to 400kg/($m^2$.s), average pressure varied from 7.5 to 10.0MPa. The main results were summarized as follows : The friction factors of $CO_2$ in the gas cooler show a relatively good agreement with those predicted by Blasius' correlation. The local heat transfer coefficient in the gas cooler has compared with most of correlations, which are the famous ones for forced convection heat transfer of turbulent flow. The results show that the local heat transfer coefficient of gas cooler agrees well with the correlation by Bringer-Smith except that at the region near pseudo critical temperature. while that at the near pseudo critical temperature is higher than the correlation.

• 대한기계학회논문집B
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• 제40권2호
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• pp.119-126
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• 2016

본 연구는 실험적인 방법과 열유동 해석 방법을 사용하여 대용량 압출형 히트싱크의 방열성능에 미치는 열원 대칭배열의 영향을 고찰하고, 이를 바탕으로 제조원가가 낮은 고효율의 히트싱크를 제안하고자 한다. 실험결과를 통해서 유사한 유효 유동단면적을 가지는 경우에 히트싱크의 전열면적이 방열성능에 큰 영향을 줌을 확인할 수 있었으며, 히트싱크의 양면 모두를 이용하는 방열이 훨씬 효과적인 방열이 가능함을 알 수 있었다. 또한, 대칭으로 열원을 배치한 경우가 비대칭 배치보다 효율적으로 방열됨을 알 수 있었다. 해석연구의 결과를 통해서는 실험결과와 정성적으로는 유사한 경향을 확인할 수 있었으며, 실험연구에서 확인하지 못한 질량유량별 및 투입열량별 추이, 단면과 양면 사용의 정량적 비교 등이 가능하였다.

• 설비공학논문집
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• 제6권4호
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• pp.365-379
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• 1994

Pool boiling experiments were carried out to study the effect of electric field on nucleate boiling heat transfer. CFC-11 and its alternative HCFC-123 were used as working fluids. Boiling on both single tube and a bundle of five tubes was investigated. Heat flux varied from 5 to $25kW/m^2$ while the applied voltage changed from 0 to 1kV. The results showed that at low heat flux where boiling was not present or very weak, electric field-induced forced convection helped increase the heat transfer coefficients of CFC-11 and HCFC-123 significantly(4-15 times increase). However, at higher heat flux, nucleate boiling of CFC-11 which is a highly dielectric fluid, was not affected significantly by the application of electric field. In contrast to CFC-11, even at high heat flux, nucleate boiling of CFC-11 which has a relatively larger electric conductivity than CFC-11, was vigorously increased up to 2-4 times. The additional power required to apply the electric field was 1-2% of the total power consumption by the heater. The increase in overall heat transfer coefficient of evaporators with HCFC -123 was about 40%, suggesting a considerable reduction in evaporator size with EHD technique.

• 한국수소및신에너지학회논문집
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• 제24권2호
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• pp.128-135
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• 2013

The nuclear fuel cycle plant is composed of various subsystems such as a fuel storage and delivery system (SDS), a tokamak exhaust processing system, a hydrogen isotope separation system, and a tritium plant analytical system. Korea is sharing in the construction of the International Thermonuclear Experimental Reactor (ITER) fuel cycle plant with the EU, Japan, and the US, and is responsible for the development and supply of the SDS. Hydrogen isotopes are the main fuel for nuclear fusion reactors. Metal hydrides offer a safe and convenient method for hydrogen isotope storage. The storage of hydrogen isotopes is carried out by absorption and desorption in a metal hydride bed. These reactions require heat removal and supply respectively. Accordingly, the rapid storage and delivery of hydrogen isotopes are enabled by a rapid cooling and heating of the metal hydride bed. In this study, we designed and manufactured a vertical-type hydrogen isotope storage bed, which is used to enhance the cooling performance. We present the experimental details of the cooling performances of the bed using various cooling parameters. We also present the modeling results to estimate the heat transport phenomena. We compared the cooling performance of the bed by testing different cooling modes, such as an isolation mode, a natural convection mode, and an outer jacket helium circulation mode. We found that helium circulation mode is the most effective which was confirmed in our model calculations. Thus we can expect a more efficient bed design by employing a forced helium circulation method for new beds.

• 한국산학기술학회논문지
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• 제15권3호
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• pp.1247-1252
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• 2014

본 연구에서는 온도조건에 따른 MR 유체의 물리적 특성을 연구하고자 침전 및 전단응력실험을 수행하였다. MR 댐퍼에 사용되는 MR 유체는 자성 파우더를 포함하고 있어 침전현상이 발생하므로 침강성과 인가전류에 의한 전단응력 변화를 상온과 고온조건에서 실험하였다. 침강특성을 조사하기 위하여 강제 대류형 오븐을 인가전류에 의한 전단응력을 측정하기 위하여 점도계를 사용하였다. 실험결과로부터 MR 유체는 시간과 온도에 따른 침강 특성이 다름을 그리고 교반시간이 큰 경우에 MR 유체의 분산성이 2배 이상 우수하였다. 전단률이 증가할수록 전단응력은 로그함수의 증가분포를 인가전류를 증가할수록 2차 함수의 증가분포를 그리고 MR 유체의 전단응력은 상온보다 고온에서 6-18% 낮은 분포를 보였다.

• 한국산학기술학회논문지
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• 제15권8호
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• pp.4749-4755
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• 2014

본 연구는 고용량 인버터 등의 열 발생 환경에서 히트싱크의 방열성능을 극대화하기 위한 파라미터 연구의 일환으로 히트싱크 베이스 두께 변화에 대한 방열성능 변화를 조사하였다. 베이스 두께가 각각 5, 9.5 및 14 mm인 히트싱크의 방열성능을 히트싱크 베이스의 윗면 중앙 온도, 히트싱크를 통한 방열량 및 열원부의 온도 등의 세 가지 지표의 비교를 통하여 고찰하였다. 실험연구와 전산유체역학 프로그램을 이용한 해석연구를 병행하여 베이스 두께 변화에 따른 각 방열 성능 지표에 변화가 있음을 확인하였다. 베이스의 윗면 중앙 온도와 방열율은 베이스의 두께가 얇을수록 향상되는 효과를 보였고, 베이스 열원부의 온도는 베이스의 두께가 두꺼울수록 낮아지는 경향을 보였다. 성능 지표의 비교 고찰을 통해 연구에 사용된 세 히트싱크 내에서는 베이스의 두께가 9.5 mm인 히트싱크에서 최적점이 나타났다. 따라서 제한적이지만 본 연구결과 내에서는 9.5 mm 두께의 베이스를 가지는 히트싱크가 최적의 방열 성능을 보이는 것으로 판단되었다.

• 한국자동차공학회논문집
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• 제19권5호
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• pp.134-142
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• 2011

Although combustion is essential in most energy generation processes, it is one of the major causes of air pollution. Exhaust pipes with circular fin were designed to study the effect of cooling the recirculated exhaust gases (EGR) of Diesel engines on the chemical composition of the exhaust gases and the reduction in the percentages of pollutant emissions. The gases examined in this study were oxides of nitrogen (NOx), carbon dioxide ($CO_2$) and carbon monoxide (CO). In addition, $O_2$ concentration in the exhaust was measured. The designs adopted in this study were about exhaust pipes with solid and hollow fins around them direct surface force measurement in water using a nano size colloidal probe technique. The direct force measurement between colloidal surfaces has been an essential topic in both theories and applications of surface chemistry. As particle size is decreased from micron size down to true Carbon nano Colloid size (<10 nm), surface forces are increasingly important. Nano particles at close proximity or high solids loading are expected to show a different behavior than what can be estimated from continuum and mean field theories. The current tools for directly measuring interaction forces such as a surface force apparatus or atomic force microscopy (AFM) are limited to particles much larger than nano size. This paper use Water and CNC fluid at normal cooling system of EGR. Experimental result showed all good agreement at Re=$2.54{\times}10^4$ by free convection and Re=$3.36{\times}10^4$ by forced air furnace.

• 전기화학회지
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• 제17권3호
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• pp.193-200
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• 2014

고분자 분리막 연료전지의 성능향상을 위해 분리판 유로설계연구는 필요하다. PEMFC의 성능향상에 대한, 강제대류를 이용한 interdigitated 유로가 최근에 많이 연구되고 있다. 이 논문에서는 interdigitated 유로를 배플들이 있는 평행류 채널에 비슷하게 적용하였다. 상용 multiphysics program인 COMSOL을 이용하여 완전차단배플인 FBB가 있는 평행류 채널에 관해 전산해석을 수행하였고 3가지 변인들(배플 위치, 유체 방향, 유체 속도)이 사용 되었다. 각각 변인들의 출력은 최대출력의 80%를 고려한 0.5V에서의 결과이다. 최종적으로, 실험설계법 중 완전요인실험법을 바탕으로 여러 수준을 갖는 각 실험인자로부터 결론을 도출하였다. 실험인자들의 주효과와 상호작용 분석은 출력을 향상시키는데 가장 영향을 주는 인자를 찾는데 유용하였다.

• 대한조선학회논문집
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• 제46권1호
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• pp.1-9
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• 2009

Three-dimensional characteristics of fluid flow and heat transfer around a wavy circular cylinder having sinusoidal variation in cross sectional area along the spanwise direction are numerically investigated using the immersed boundary method. The three different wavelengths of ${\pi}4$, ${\pi}3$ and ${\pi}2$ at the fixed wavy amplitude of 0.1 have been considered to investigate the effects of waviness especially on the forced convection heat transfer around a wavy cylinder when the Reynolds and Prandtl numbers are 300 and 0.71, respectively. The present computational results for a wavy cylinder are compared with those for a smooth cylinder. The time- and total surface-averaged Nusselt number for a wavy cylinder with ${\lambda}={\pi}/2$ is larger than that for a smooth cylinder, whereas that with ${\lambda}={\pi}/4$ and ${\pi}/3$ is smaller than that for a smooth cylinder. However, because the surface area exposed to heat transfer for a wavy cylinder is larger than that for a smooth cylinder, the total heat transfer rate for a wavy cylinder with different wavelengths of ${\lambda}={\pi}/4$, ${\pi}/3$ and ${\pi}/2$ is larger than that for a smooth cylinder.