• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.3142-3147
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• 2008

A simple transient simulation of ground source heat pump system was carried out to investigate the effects of ground thermal conductivity on its performance. The TRNSYS code with a simple water to water heat pump model was used to compare the COP variation of the system. A new ground heat exchanger called by semi-closed loop was proposed and constructed in the real site. The effective thermal conductivity was measured using the test equipment developed by according to the line source model. The simulation results showed that highly efficient thermal conductivity of the grout material could increase the performance of the heat pump system very well. And the new ground heat exchanger showed the increased effective thermal conductivity as the penetration water flow rate(PWFR) was increased. Therefore, the performance improvement of the heat pump system using the proposed ground heat exchanger can be expected.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1997년도 추계학술대회 논문집
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• pp.447-450
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• 1997

Temperature distribution measurements in the mockup apparatus of reactor vessel were performed to determine the effective thermal conductivity of Al powder porous media where stainless steel tubes were installed with different geometry. The temperature distributions at four separated sections with different arrangements of porous media have different slopes according to the geometrical configuration. From the measured temperature distribution, effective thermal conductivity have been derived using the least square fitting method.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 춘계학술대회
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• pp.33-36
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• 2006

The effective thermal conductivities of $Mm\;(La_{0.6-0.8})\;Ni_{4.0}Co_{0.6}Mn_{0.2}Al_{0.2}$ (TL-492) with hydrogen and helium have been examined. Experiment results show that pressure has great influence on effective thermal conductivity in Low pressure range (below 0.5 MPa). And that influence decreases rapidly with increase of gas pressure. The reason is at low pressure, the mean free path of gas becomes greater than effective thickness of gas film which is important to the heat transfer mechanism in this research. And, carbon fibers have been used to try to enhance the poor thermal conductivity of TL-492. Three types of carbon fibers and three mass fractions have been examined and compared. Naturally, the highest effective thermal conductivity has been reached with carbon fiber which has highest thermal conductivity, and highest mass fraction. This method has acquired 4.33 times higher thermal conductivity than pure metal hydrides with quite low quantity of additives, only 0.99wt% of carbon fiber. This is a good result comparing to other method which can reach higher effect ive thermal conductivity but needs much higher mass fraction of additives too.

• 한국지반공학회논문집
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• 제39권9호
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• pp.5-11
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• 2023

지반구조물의 해석에 있어서 해석의 고려 대상과 분야가 점점 다변화되고 있으며, 특히 지반동결과 관련된 분야에서 지반재료의 열적거동 특성에 대한 예측의 필요성이 중요해지고 있다. 신뢰성 있는 지반의 동결거동 평가를 위해서는 다양한 조건에서의 시료의 유효 열전도도 변화에 대한 고려가 필요하다. 본 논문에서는 시료의 간극률, 초기 포화도, Read time 설정을 달리하여 탐침 실험을 수행하였고, 이를 통해 동결 사질토의 유효 열전도도에 영향을 미치는 인자들을 평가하였다. 서로 다른 간극률 조건에서 실험을 수행한 결과, 시료의 간극률이 작을수록 동결토의 유효 열전도도는 증가하는 경향이 나타났다. 반면, 시료의 포화도가 증가할수록 동결토의 유효 열전도도는 증가하였다. 유효 열전도도 측정에 대한 계측기 Read time 설정의 민감도가 존재하였는데, Read time을 1분으로 설정하여 측정하였을 때 측정값의 범위가 국내의 선행연구결과와 유사하게 나타났다.

• 설비공학논문집
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• 제13권1호
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• pp.18-24
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• 2001

Woven wire wick is very effective structure because of its easiness to insert inside of pipe for a miniature heat pipe. The present study was conducted to investigate the effect of the effective flow passage with respect to wire helix angle. Also effective thermal conductivity were examined by defining mean porosity considering effective liquid flow passages. Effective heat transfer area is varied with respect to wire helix angle, and in the range of $\thet=60~65^{\circ}C$, heat transfer area is decreased about 15~20%. Permeability of woven wire wick shows similar value of 200 mesh screen wick. And comparison of experimental results on effective thermal conductivity shows a fairly good agreement with the analytical results.

• 한국전자파학회논문지
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• 제20권4호
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• pp.406-412
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• 2009

본 연구에서는 주변 환경이 복잡하고 토양의 특성이 잘 알려지지 않은 지역에서는 적용이 가능한 중파대역 유효 대지 도전율 계산법을 제안하였다. 제안된 방법은 해안 기지국에서 측정된 전계 강도와 일반적인 중파대역 감쇠 모델을 이용하여 유효 대지 도전율을 계산하며, 오차를 최소화하기 위해 통계적인 방법을 이용하였다. 다음으로, 제안된 방법을 이용하여 국내의 중파대역 유효 대지 도전율을 얻었으며, 전계 강도 비교 및 오차 분석을 통해 제안된 방법의 정확도와 유용성을 확인하였다.

• Nuclear Engineering and Technology
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• 제49권3호
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• pp.459-465
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• 2017

The goal of this study is to evaluate the effective thermal conductivity and diffusivity of containment walls as heat sinks or passive cooling systems during nuclear power plant (NPP) accidents. Containment walls consist of steel reinforced concrete, steel liners, and tendons, and provide the main thermal resistance of the heat sinks, which varies with the volume fraction and geometric alignment of the rebar and tendons, as well as the temperature and chemical composition. The target geometry for the containment walls of this work is the standard Korean NPP OPR1000. Sample tests and numerical simulations are conducted to verify the correlations for models with different densities of concrete, volume fractions, and alignments of steel. Estimation of the effective thermal conductivity and diffusivity of the containment wall models is proposed. The Maxwell model and modified Rayleigh volume fraction model employed in the present work predict the experiment and finite volume method (FVM) results well. The effective thermal conductivity and diffusivity of the containment walls are summarized as functions of density, temperature, and the volume fraction of steel for the analysis of the NPP accidents.

• 한국지하수토양환경학회지:지하수토양환경
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• 제22권3호
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• pp.27-41
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• 2017

This study dealt with the characteristics and the interrelations of hydrogeological parameters such as hydraulic conductivity, dispersivity and effective porosity of unconsolidated sediments for providing the basic data necessary for the planning of the management and preservation of groundwater quality in the Nakdong River Delta of Busan City, Korea. Groundwater quality in this area has been deteriorated due to seawater intrusion, agricultural fertilizer and pesticide, industrial wastewater, and contaminated river water. The physical properties (grain size distribution, sediment type, sorting) and aquifer parameters (hydraulic conductivity, effective porosity, longitudinal dispersivity) were determined from grain size analysis, laboratory permeability test and column tracer test. Among 36 samples, there were 18 Sand (S), 7 Gravelly Sand (gS), 5 Silty Sand (zS), 5 Muddy Sand (mS), and 1 Sandy Silt (sZ). Hydraulic conductivity was determined through a falling head test, and ranged from $9.2{\times}10^{-5}$ to $2.9{\times}10^{-2}cm/sec$ (0.08 to 25.6 m/day). From breakthrough curves, dispersivity was calculated to be 0.35~3.92 cm. Also, effective porosity and average linear velocity were obtained through the column tracer test, and their values were 0.04~0.46 and 1.06E-04~6.49E-02 cm/sec, respectively. Statistical methods were used to understand the interrelations among aquifer parameters of hydraulic conductivity, effective porosity and dispersivity. The relation between dispersivity and hydraulic conductivity or effective porosity considered the sample length, because dispersivity was affected by experimental scale. The relations between dispersivity and hydraulic conductivity or effective porosity were all in inverse proportion for all long and short samples. The reason was because dispersivity was in inverse proportion to the groundwater velocity in case of steady hydrodynamic dispersion coefficient, and groundwater velocity was in proportion to the hydraulic conductivity or effective porosity. This study also elucidated that longitudinal dispersivity was dependent on the scale of column tracer test, and all hydrogeological parameters were low to high values due to the sand quantity of sediments. It is expected that the hydrogeological parameter data of sediments will be very useful for the planning of groundwater management and preservation in the Nakdong River Delta of Busan City, Korea.

• 설비공학논문집
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• 제11권2호
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• pp.185-192
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• 1999

Effective thermal conductivities and pressure-drop-related properties of aluminum foam metals have been measured. The effects of porosity and cell size in the aluminum foam metal are investigated in detail. The porosity of the foam metal, considered in the present study, varies from 0.89 to 0.96 and the cell size from 0.65㎜ to 2.5㎜. The effective thermal conductivity is evaluated by comparing the temperature gradient of the foam metal with that of the thermal conductivity-known material. The pressure drop in the foam metal is measured by a highly precise electric manometer while air is flowing through the aluminum foam metal in the channel. The results obtained indicate that the effective thermal conductivities are found to be increased with a decrease in the porosity while the effective thermal conductivities ire little affected by the cell size at a fixed porosity. However, the pressure drop is strongly affected by the cell size as well as the porosity. It is seen that the pressure drop is increased as the cell size becomes smaller, as expected. The minimum pressure drop is obtained in the porosity 0.94 at a fixed cell size. A new correlation of the pressure drop is proposed based on the permeability and Ergun's coefficient for the aluminum foam metal.

• Geomechanics and Engineering
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• 제25권2호
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• pp.159-170
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• 2021

Particle size of tailings in different areas of dams varies due to sedimentation and separation. Saturated hydraulic conductivity of high-stacked talings materials are seriously affected by void ratio and particle breakage. Conjoined consolidation permeability tests were carried out using a self-developed high-stress permeability and consolidation apparatus. The hydraulic conductivity decreases nonlinearly with the increase of consolidation pressure. The seepage pattern of coarse-particle tailings is channel flow, and the seepage pattern of fine-particle tailings is scattered flow. The change rate of hydraulic conductivity of tailings with different particle sizes under high consolidation pressure tends to be identical. A hydraulic conductivity hysteresis is found in coarse-particle tailings. The hydraulic conductivity hysteresis is more obvious when the water head is lower. A new hydraulic conductivity-void ratio equation was derived by introducing the concept of effective void ratio and breakage index. The equation integrated the hydraulic conductivity equation with different particle sizes over a wide range of consolidation pressures.