• Journal of Advanced Marine Engineering and Technology
• /
• v.39 no.4
• /
• pp.363-367
• /
• 2015

In this study, a high performance Bubble Jet Loop Heat Pipe (BJLHP) was developed using the enhanced nucleate boiling surfaces in an evaporating section. A sintered tube and GEWA-T(Wieland) tube were used enhance nucleate boiling. The thermal performance of these BJLHP was compared with the conventional smooth tube BJLHP with an effective thermal conductivity. This experiment was conducted under the following conditions : working fluid, charging ratio and input power of R-141b, 50%vol., 75W and 100W, respectively. As a result, the effective thermal conductivity of BJLHP with a sintered tube in the evaporating section was 300% higher than the smooth tube BJLHP.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.25 no.4
• /
• pp.315-321
• /
• 2012

In this study, a sequential multiscale homogenization method to characterize the effective thermal conductivity of nano particulate polymer nanocomposites is proposed through a molecular dynamics(MD) simulations and a finite element-based homogenization method. The thermal conductivity of the nanocomposites embedding different-sized nanoparticles at a fixed volume fraction of 5.8% are obtained from MD simulations. Due to the Kapitza thermal resistance, the thermal conductivity of the nanocomposites decreases as the size of the embedded nanoparticle decreases. In order to describe the nanoparticle size effect using the homogenization method with accuracy, the Kapitza interface in which the temperature discontinuity condition appears and the effective interphase zone formed by highly densified matrix polymer are modeled as independent phases that constitutes the nanocomposites microstructure, thus, the overall nanocomposites domain is modeled as a four-phase structure consists of the nanoparticle, Kapitza interface, effective interphase, and polymer matrix. The thermal conductivity of the effective interphase is inversely predicted from the thermal conductivity of the nanocomposites through the multiscale homogenization method, then, exponentially fitted to a function of the particle radius. Using the multiscale homogenization method, the thermal conductivities of the nanocomposites at various particle radii and volume fractions are obtained, and parametric studies are conducted to examine the effect of the effective interphase on the overall thermal conductivity of the nanocomposites.

• The Journal of Engineering Geology
• /
• v.13 no.4
• /
• pp.419-428
• /
• 2003

In order to evaluate groundwater movement and the infiltration of contaminants, such as petroleum products, the determination of porosity and effective porosity is very important. Porosity and effective porosity are important physical parameters that determine the transfer and movement of water and solutes in porous media. Various methods of determining these parameters have been developed, with varying degrees of accuracy and applicability. Most of the existing methods produce static results. They do not produce instantaneous and real time of porosity and effective porosity in a porous media. In this study, we used a new permittivity method called Frequency Domain Reflectometry with Vector analyzer (FDR-V) to determine the porosity and effective porosity of some sand samples in the laboratory. The advantage of the FDR-V method is that it instantaneously determines the temporal variation of dielectric constants of porous media. Then, the porosity and the effective porosity of porous media are computed using well established empirical equations. Results obtained from the FDR-V method compared favorably with results from other permittivity methods such as gravimetric, injection and replacement tests. The ratio of effective porosity to porosity was 85 - 92 %, when FDR-V was used. This value compared favourably with 90 %, which has been usually quoted in previous studies. Considering the convenience and its applicability, the EDR-V permittivity holds a great potential in porous media and contaminant transport studies.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.32 no.4C
• /
• pp.169-175
• /
• 2012

Soil water retention characteristics are influenced by factors of the confining stress and hysteresis in the variably saturated soil. In the description of effective stress based on hydraulic characteristics, the contribution of a matric suction to effective stress then varies with depth or is different between the processes of infiltration and evaporation. Unsaturated effective stress can be described based on suction stress characteristic curve, in which a representative soil water retention curve is required to evaluate. Pressure palate extractor tests under various confining stresses were performed and the hysteresis of drying and wetting process was also acquired. In the process of drying or wetting, a unique relationship has been estimated on the effective volumetric water content and the matric suction, which defines suction stress characteristic curve. In the unsaturated shear strength from triaxial tests, the suction stress and the effective stress were evaluated by matric suctions. The failure envelop by effective stress based on soil water retention characteristics was unique and the same as the saturated one. The measured suction stress from triaxial tests was similar to that from the soil water retention curve. Therefore it is verified that a representative soil water retention curve can be defined which is independent of the confining effect under wetting or drying process of the hysteresis.

• Geophysics and Geophysical Exploration
• /
• v.13 no.1
• /
• pp.80-87
• /
• 2010

This study was conducted to develop a reservoir modelling workflow to reproduce the heterogeneous distribution of effective permeability that impacts on the performance of SAGD (Steam Assisted Gravity Drainage), the in-situ bitumen recovery technique in the Athabasca Oil Sands. Lithologic facies distribution is the main cause of the heterogeneity in bitumen reservoirs in the study area. The target formation consists of sand with mudstone facies in a fluvial-to-estuary channel system, where the mudstone interrupts fluid flow and reduces effective permeability. In this study, the lithologic facies is classified into three classes having different characteristics of effective permeability, depending on the shapes of mudstones. The reservoir modelling workflow of this study consists of two main modules; facies modelling and permeability modelling. The facies modelling provides an identification of the three lithologic facies, using a stochastic approach, which mainly control the effective permeability. The permeability modelling populates mudstone volume fraction first, then transforms it into effective permeability. A series of flow simulations applied to mini-models of the lithologic facies obtains the transformation functions of the mudstone volume fraction into the effective permeability. Seismic data contribute to the facies modelling via providing prior probability of facies, which is incorporated in the facies models by geostatistical techniques. In particular, this study employs a probabilistic neural network utilising multiple seismic attributes in facies prediction that improves the prior probability of facies. The result of using the improved prior probability in facies modelling is compared to the conventional method using a single seismic attribute to demonstrate the improvement in the facies discrimination. Using P-wave velocity in combination with density in the multiple seismic attributes is the essence of the improved facies discrimination. This paper also discusses sand matrix porosity that makes P-wave velocity differ between the different facies in the study area, where the sand matrix porosity is uniquely evaluated using log-derived porosity, P-wave velocity and photographically-predicted mudstone volume.

• Proceedings of the Acoustical Society of Korea Conference
• /
• 1992.11a
• /
• pp.69-76
• /
• 1992

섬유강화 복합재료의 동탄성계수와 감쇠특성을 규명하기 위하여 랜덤하게 분포된 무한 실린더 형상의 산란체를 가진 점탄성 매질내에서 , 축방향으로 분극되어 조화 운동을 하는 탄성파의 전파에 관하여 연구하였다. 다중 산란에 관한 이론으 이용하여 매질내에서의 파동전파 특성을 내포하는 분산관계식을 얻었다. 다중산란에 의한 실린더간의 상호작용을 수식화하기위하여 필요한 실린더의 쌍분포함수는 몬테카를로 모의 실험을 이용하여 구하였다. 수치적으로 구한 감쇠계수 및 유효전단강성을 주파수와 체적율의 함수로 제시하였다. 또한 감쇠계수의 주파수에 따른 변화에 있어서, 저주파에서는 매질의 점탄성 손실이 지배적이며, 고주파수로 갈수록 다중산란에 의한 손실이 지배적인 것으로 나타났다.

• Journal of Ocean Engineering and Technology
• /
• v.11 no.2
• /
• pp.39-47
• /
• 1997

Creep rate the elevated temperature is known to be controller by the softening process of microstructure especially in the solid solution alloys such as 125 Cr rotor steel. The change of structure is a decreasing process of the free energy of the state including stress, diffusivity of the material, and tmeperature. This study shows that diffusion coefficient, D of 12% Cr rotor steel at 953K with 74.8 MPa is 1.084~3.140*$10^{15}mm^2sec^1$ compared to $1.658*10^{24}mm^2sec^1$at 963K without stress. During creep, the growth of martensite laths accelerates the diffusion coefficient under stress due to incoherency of interface between carbides and matrix.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.8 no.6
• /
• pp.599-603
• /
• 1984

Field equations describing the effective behavior of general heterogeneous media are derived from the integral balance relations through the methods of distribution and convolution.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.20 no.1
• /
• pp.60-66
• /
• 2011

In this paper, the computer simulation analyzed the effective plastic strain and temperature behaviors. The quantitative analyses which proposed the effective mold design of S/CAM shaft was executed. The parameters of forging shape that affected on the optimize conditions that was calculated with simple equation were investigated. it is expected that the developed analysis model and design technique would greatly contribute to the drum brake optimal design considering effective plastic strain and temperature affected behaviors. This development could save more than 20% of production cost and reduced failure rate to more than 30%. By improving the life span of mold from 15,000 to 25,000, financial difficulty of company imposed on a mold manufacture could be overcome.

• Journal of Global Scholars of Marketing Science
• /
• v.3
• /
• pp.1-21
• /
• 1999

국내의 지역간 격차에 주목하는 과거의 지역발전전략은 더 이상 유효성을 확보할 수 없게 되었다. 왜 이러한 변화가 나타나고 있으며, 새로운 전략 컨셉트는 무엇인가? 어떤 전략대안이 개발될 수 있으며, 그것을 실천할 수 있는 방법은 무엇인가? 이것이 본 연구가 제기하는 기본적 질문이다. 새로운 패러다임의 핵심은 인간의 내적 지식만이 우리의 미래상을 제시하고 환경변화에 대응할 수 있는 방향을 제시해 줄 수 있다는 것이다. 따라서 지역발전을 어떻게 인식하느냐에 따라 지역발전의 방향은 바뀌게 되어 있다. 세계적 네트워크시스템 하에서 한 지역의 의미는 집합체적 학습과 혁신이 가속화될 수 있는 공간이라는 측면에서 그 중요성이 부각되고 있는 현실을 직시해야 한다. 그래야 차별화에 의한 동태적 경쟁우위를 확보하면서 성장과 발전을 지속할 수 있게 된다. 지역발전 전략 컨셉트의 변화는 새로운 전략대안의 개발을 강요하고 있으며, 지역특화산업집락(RC)의 개발과 육성으로 구체화되고 있다. 본 연구에서는 "입체다이아몬드모형" 을 개발하여 각 지역의 RC개발전략 수집과 실천의 방향을 제시하고 있다.