• Journal of the Korean Geotechnical Society
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• v.26 no.2
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• pp.45-54
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• 2010

The SCW numerical model described in the companion paper was used to carry out a comprehensive parametric study to evaluate the performance of the SCW. The five ground related parameters, which are porosity, hydraulic conductivity, thermal conductivity, specific heat, geothermal gradient, and five SCW design parameters, which are pumping rate, well depth, well diameter, dip tube diameter, bleeding rate, were used in the study. Two types of numerical simulations were performed. The first type was used to perform short-term (24-hour) simulation, while the second type 14 day simulation. The study results indicate that the parameters that have important influence on the performance of SCW were hydraulic conductivity, thermal conductivity, geothermal gradient, pumping rate, and bleeding rate. The thermal conductivity had the most important influence on the performance of the SCW. With the increase in the geothermal gradient, the performance increased in the heat mode, but decreased in the cooling mode. The hydraulic conductivity influenced the performance when the value was larger than $10^{-4}m/s$. The depth of the well increased the performance, but at the cost of increased cost of boring. The bleeding had an important influence on SCW, greatly enhancing the performance at a limited increased cost of operation. Overall, this study showed that various factors had a cumulative influence on the performance of the SCW, and a numerical simulation can be used to accurately predict the performance of the SCW.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.2
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• pp.119-125
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• 2017

Ablative material in a rocket nozzle is exposed to high temperature combustion gas, thus undergoes complicated thermal/chemical change in terms of chemical destruction of surface and thermal decomposition of inner material. Therefore, method for conjugate analysis of thermal response inside carbon/phenolic material including rocket nozzle flow, surface chemical reaction and thermal decomposition is developed in this research. CFD is used to simulate flow field inside nozzle and conduction in the ablative material. A change in material density and a heat absorption caused by the thermal decomposition is considered in solid energy equation. And algebraic equation under boundary layer assumption is used to deduce reaction rate on the surface and resulting destruction of the surface. In order to test the developed method, small rocket nozzle is solved numerically. Although the ablation of nozzle throat is deduced to be higher than the experiment, shape change and temperature distribution inside material is well predicted. Error in temperature with experimental results in rapid heating region is found to be within 100 K.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.78-78
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• 2003

레이져 플래시법은 고온에서 열물성을 측정하는 수단으로 가장 많이 사용되고 있는 방법으로 알려져 있다. 각종재료의 열전도도를 측정하는 방법들이 많으나 열평형 유지, 고온, 측정시간등의 제약으로 열확산도측정이 간편하고 고온까지 가능하므로 이에 대한 측정법이 일반화되어 있다. 레이져 플레시법은 열확산도를 1초이내 측정가능하고 200$0^{\circ}C$까지 장치구현이 가능하므로 가장 많이 이용되고 있다. 그러나 장치의 검증을 위한 열확산도 표준물질이 필요로 하나 현재 열전도도 기준물질을 이용하여 검증하고 있으나 향후 열확산도 기준물질의 개발이 현재 시급하다. 현재까지 그라파이트를 중심으로한 고열전도도 연구가 진행되고 있으며, 현재 국제기관에 의해 인증된 기준물질이 부족한 실정이다. 본 연구에서는 기준물질로서 가능성을 탐색하고자 이용이 가장 많은 금속을 택하였다. 현재 텅스텐 및 몰리브덴이 고온까지 안정적이므로 두가지 재료를 택하여 실험을 수행하였다. 먼저 상온~1000K온도영역에서 열확산도 측정연구를 수행하였다. 측정된 데이터 값은 TPRC값과 비교하여 10%이내의 오차를 보였으며 고온에서 높은 안정성을 나타냄을 확인할 수 있었다. 아울러 계측시스템의 자동화 및 개량화를 통하여 실험과정에서 발생할 수 있는 오차를 줄였다. 열확산도 해석은 대수법(logarithmic법)과 Parker법을 이용하여 분석하였으며, 레이져에너지 및 시료크기에 따른 영향을 고려하여 여러가지 크기의 시편을 가지고 실험하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.10
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• pp.4392-4397
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• 2012

In this study, we used the commercial package (Unigraphics) to construct a junction box cable car when laser plastic parts have been processed using urethane resin(TSR-755) as a starting mold material. After construction, we carried out the filing, packing, cooling, and deforming analyzation using Injection Molding Analysis (Simpoe-Mold) to determine the gate positioning and automatic cooling cycle through the examination. The results show that inserting into the injection mold after processing ceramic has reduced the time of thermal conductivity of molding and cooling; and quick selection of gates and cooling lines could possibly cause an improvement of productivity.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.40-40
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• 2003

일반적으로 액티브 매트릭스 구동용 스위칭 소자의 경우 Turn-on 시간은 프레임 주파수와 게이트 라인의 수에 반비례하므로 LCD의 화면이 대면적으로 갈수록 스위칭 주파수는 증가하고 이는 채널에서의 열적 효과(thermal effect)를 유도하게 된다. 그러므로 전도성 유기물이 LCD용 유기박막트랜지스터(Thin Film Transistor) 등의 부품으로서의 적절성을 판단하기 위하여는 이에 대한 열적 특성에 대한 검증이 필요하게 된다. 따라서 본 연구에서는 유기 TFT의 열설계에 있어서 필수적인 물질변수로 인식되는 열적 특성들을 측정 계산하였으며 이를 소자의 열적 모델링에 적용하였다. 실험물질로는 pentacene을 사용하였으며 열확산도는 레이저 플레쉬법을 이용하여 측정하였다. 별도로 측정된 비열ㆍ밀도 등의 물성특성을 이용하여 상온에서 200 C의 온도범위에서 pentacene의 열전도도를 계산하여 그 결과를 열적으로 해석하였다. 계산결과, pentacene의 열전도도는 상온에서 약 0.0024 W/cm K의 값을 나타내었고, 70 C 까지 증가하여 약 0.0035 W/cm K의 정점을 보인 후에 200 C 에서 약 0.0022 W/cm K의 낮은 값을 나타낼 때까지 계속 감소하였다 아울러 본 연구에서는 실제 소자응용 시 박막으로서의 pentacene의 응용을 고려하여 실제 박막형태에 대한 열전도를 측정하였으며 이를 레이저 플레쉬법으로 측정한 값과 비교ㆍ분석하였다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.3
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• pp.241-249
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• 1984

두 개의 긴 수직평판핀을 가진 등온수평원통으로 부터의 자연대류 열전달을 2차원 유한차분법에 의한 수치해석으로 연구하였다. 축방향의 두 수직평판핀을 가진 수평원통으로 부터의 열전달은 Ra=$10^{6}$, Pr=5 및 무차원 $K_{f}$t/KD=0.5인 경우에 보통 원통에서의 열전도보다 5.32% 증가되었다. Ra와 Pr가 증가하면 국소핀 누셀트수는 증가하고 무차원핀 온도는 감소된다. 그 러나 무차원핀 변수가 증가하면 국소핀 누셀트수와 무차원핀 온도분포는 증가된다. 최대국소핀 누셀트수는 Ra=$10^{6}$인 경우에 상향핀과 하향핀의 (r-r$_{0}$)=0.1-0.2에서 존재한다. 수 직핀을 가진 원통주위에서 부력 유도된 유동은 보통 원통에서 보다 더욱 활발하였다. 따라서 Ra=$10^{6}$ , Pr=5인 경우에 핀 근방에서의 무차원 무차원반경 방향 속도는 보통원통의 경 우보다 큰 값을 가진다.다.다.

• Composites Research
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• v.37 no.3
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• pp.170-178
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• 2024

This study proposes a hybrid composite where a thin copper film (Cu film) is embedded in carbon fiber reinforced plastic (CFRP), and quantum annealing is applied to derive the combination of Cu film placement that maximizes the through-thickness thermal conductivity. The correlation between each ply of CFRP and the Cu film is analyzed through finite element analysis, and based on the results, a combination optimization problem is formulated. A formalization process is conducted to embed the defined problem into quantum annealing, resulting in the formulation of objective functions and constraints regarding the quantity of Cu films that can be inserted into each ply of CFRP. The formulated equations are programmed using Ocean SDK (Software Development Kit) and Leap to be embedded into D-Wave quantum annealer. Through the quantum annealing process, the optimal arrangement of Cu films that satisfies the maximum through-thickness thermal conductivity is determined. The resulting arrangements exhibit simpler patterns as the quantity of insertable Cu films decreases, while more intricate arrangements are observed as the quantity increases. The optimal combinations generated according to the quantity of Cu film placement illustrate the inherent thermal conductivity pathways in the thickness direction, indicating that the transverse placement freedom of the Cu film can significantly affect the results of through-thickness thermal conductivity.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.6
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• pp.779-787
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• 2007

This paper presents a highly efficient moving least squares finite difference method (MLS FDM) for a heat transfer problem of bi-material with interfacial boundary. The MLS FDM directly discretizes governing differential equations based on a node set without a grid structure. In the method, difference equations are constructed by the Taylor polynomial expanded by moving least squares method. The wedge function is designed on the concept of hyperplane function and is embedded in the derivative approximation formula on the moving least squares sense. Thus interfacial singular behavior like normal derivative jump is naturally modeled and the merit of MLS FDM in fast derivative computation is assured. Numerical experiments for heat transfer problem of bi-material with different heat conductivities show that the developed method achieves high efficiency as well as good accuracy in interface problems.

• Journal of Energy Engineering
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• v.10 no.4
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• pp.349-356
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• 2001

Phenomenon of direct contact condensation (DCC) heat transfer between steam and water is characterized by the transport of heat and mass through a moving steam/water interface. Since the DCC heat transfer provides some advantageous features in the viewpoint of enhanced heat transfer, it is widely applied to the diversified industries. This study proposes a simple condensation model on the stable steam jets discharging into a quenching tank with subcooled water from a single horizontal pipe for the prediction of the steam jet shapes. The model was derived from the mass, momentum and energy equations as well as thermal balance equation with condensing characteristics at the steam/water interface for the axi-symmetric coordinates. The extremely large heat transfer rate at the steam/water interface was reflected in the effective thermal conductivity estimated from the previous experimental results. The results were compared with the experimental ones. The predicted steam jet shape(i. e. radius and length) by the model was increasing as the steam mass flux and the pool temperature were increasing, which was similar to the trend observed in the experiment.

• Journal of Bio-Environment Control
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• v.18 no.4
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• pp.341-347
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• 2009

Experiments and computations were conducted to investigate the heat insulation characteristics of multi layer materials for cultivation greenhouse. In case of the experiments, measurements of temperature were carried out with a K-type thermocouples and data logger to research the heat transfer in the experimental module generated by the heat source. A thermal conductivity meter, QTM-500 based on modified transient hot wire method was used to measure the thermal conductivity of multi layer materials. The numerical analyses were performed by commercial code CFX-11 according to the variation of multi layer materials without air layer. The experimental results showed that the heat insulation of multi layer materials was higher than single layer materials by 50~90%. It was found that the effect of heat insulation was raised by the combination of multi layer materials.