• Title/Summary/Keyword: Thermal conductivity

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Predicting the Effective Thermal Conductivity of Some Sand-Water Mixtures Used for Backfilling Materials of Ground Heat Exchanger (지중열교환기 뒤채움재로 사용되는 모래-물 혼합물의 열전도도 예측)

  • Sohn, Byong-Hu
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.20 no.9
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    • pp.614-623
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    • 2008
  • This paper presents the results of a laboratory study on the thermal conductivity of and(silica, quartzite, limestone, sandstone, granite and two masonry sands)-water mixtures used for ground heat exchanger backfilling materials. Nearly 260 tests were performed in a thermal conductivity measuring system to characterize the relationships between the thermal conductivity of mixtures and the water content. The experimental results show hat the thermal conductivity of mixtures increases with increasing dry density and with increasing water content. The most widely used empirical prediction models for thermal conductivity of soils were found inappropriate to estimate the thermal conductivity of unsaturated sand-water mixtures. An improved model using an exponential relationship to compute the thermal conductivity of dry sands and empirical relationship to assess the normalized thermal conductivity of unsaturated sand-water mixtures is presented.

Predicting the Effective Thermal Conductivity of Sand-Water Mixtures Used for Grouting Materials (그라우팅 재료로 사용되는 모래-물 혼합물의 열전도도 예측)

  • Sohn, Byong-Hu;Lim, Hyo-Jae
    • Proceedings of the SAREK Conference
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    • pp.761-768
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    • 2008
  • This paper presents the results of a laboratory study on the thermal conductivity of sand(silica, quartzite, limestone, sandstone, granite and masonry sand)-water mixtures used in ground heat exchanger backfilling materials. Nearly 260 tests were performed in a thermal conductivity measuring system to characterize the relationships between the thermal conductivity of mixtures and the water content. The experimental results show that the thermal conductivity of mixtures increases with increasing dry density and with increasing water content. The most widely used empirical prediction models for thermal conductivity of soils were found inappropriate to estimate the thermal conductivity of unsaturated sand-water mixtures. An improved model using a exponential relationship to compute the thermal conductivity of dry sands and empirical relationship to assess the normalized thermal conductivity of unsaturated sand-water mixtures is presented.

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Thermal Conductivity Measurement of Grouting Materials for Ground Heat Exchanger Borehole (지중 열교환기 보어홀 그라우팅 재료의 열전도도 측정)

  • Sohn, Byong-Hu;Shin, Hyun-Joon
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.18 no.6
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    • pp.493-500
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    • 2006
  • This paper concerns the measurement of thermal conductivity of grouting materials for ground loop heat exchanger. A thermal conductivity meter, QTM-500 based on modified transient hot wire method was used to measure the thermal conductivity of neat bentonite and mixtures of bentonite and various additives. Relative to the total mixture mass, as the percent additive was increased the mixture thermal conductivity increased. For the bentonite-silica sand mixtures, the higher density of the sand particles resulted in much higher mixture thermal conductivity. The quartzite and silica sands produced the largest increases in mixture thermal conductivity, while common masonry and limestone sands produced lower thermal conductivity increases.

Thermal Conductivity Measurement of Sand-Water Mixtures Used for Backfilling Materials of Vertical Boreholes or Horizontal Trenches (지중열교환기 수직 보어홀 및 수평 트렌치 뒤채움재로서 모래-물 혼합물의 열전도도 측정)

  • Sohn, Byong-Hu
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.20 no.5
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    • pp.342-350
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    • 2008
  • This paper presents the results of a laboratory study on the thermal conductivity of sand (silica, quartzite, limestone and masonry sand)-water mixtures used in ground heat exchanger backfilling materials. Nearly 150 tests were performed in a thermal conductivity measuring system (TPSYS02) to characterize the relationships between the thermal conductivity of mixtures and the water content. The results show that the thermal conductivity of mixtures increases with increasing dry density and with increasing water content. The results also show that for constant water contents and a dry density value, the thermal conductivity of mixtures increases with increasing thermal conductivity of solid particles. The measurement results were also compared with the most widely used empirical prediction models for the thermal conductivity of soils.

Characterization of Lattice Thermal Conductivity in Semiconducting Materials (반도체 재료의 격자열전도도 분석)

  • Lim, Jong-Chan;Yang, Heesun;Kim, Hyun-Sik
    • Journal of the Microelectronics and Packaging Society
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    • v.27 no.4
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    • pp.61-65
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    • 2020
  • Suppressing lattice thermal conductivity of thermoelectric materials is one of the most popular approach to improve their thermoelectric performance. However, accurate characterization of suppressed lattice thermal conductivity is challenging as it can only be acquired by subtracting other contributions to thermal conductivity from the total thermal conductivity. Here we explain that electronic thermal conductivity (for all materials) and bipolar thermal conductivity (for narrow band gap materials) need to be determined accurately first to characterize the lattice thermal conductivity accurately. Methods to calculate Lorenz number for electronic thermal conductivity (via single parabolic model and using a simple equation) and bipolar thermal conductivity (via two-band model) are introduced. Accurate characterization of the lattice thermal conductivity provides a powerful tool to accurately evaluate effect of different defect engineering strategies.

Experimental investigation on the variation of thermal conductivity of soils with effective stress, porosity, and water saturation

  • Lee, So-Jung;Kim, Kyoung-Yul;Choi, Jung-Chan;Kwon, Tae-Hyuk
    • Geomechanics and Engineering
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    • v.11 no.6
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    • pp.771-785
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    • 2016
  • The thermal conductivity of soils is an important property in energy-related geotechnical structures, such as underground heat pumps and underground electric power cable tunnels. This study explores the effects of geotechnical engineering properties on the thermal conductivity of soils. The thermal conductivities of quartz sands and Korean weathered silty sands were documented via a series of laboratory experiments, and its variations with effective stress, porosity, and water saturation were examined. While thermal conductivity was found to increase with an increase in the effective stress and water saturation and with a decrease in porosity, replacing air by water in pores the most predominantly enhanced the thermal conductivity by almost one order of magnitude. In addition, we have suggested an improved model for thermal conductivity prediction, based on water saturation, dry thermal conductivity, saturated thermal conductivity, and a fitting parameter that represents the curvature of the thermal conductivity-water saturation relation.

Thermal conductivity of rocks for geothermal energy utilization (지열에너지 활용을 위한 암석의 열전도도 고찰)

  • Lee, Young-Min
    • Journal of the Korean Society for Geothermal and Hydrothermal Energy
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    • v.3 no.2
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    • pp.9-15
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    • 2007
  • Thermal conductivity of rocks is one of the most important parameters in designing a geothermal heat pump system, because heat exchange rate depends primarily on thermal conductivity of rocks. In this paper, the measurement methods of thermal conductivity, thermal conductivity of rocks, and heat exchange rate are discussed.

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Thermal transport study in actinide oxides with point defects

  • Resnick, Alex;Mitchell, Katherine;Park, Jungkyu;Farfan, Eduardo B.;Yee, Tien
    • Nuclear Engineering and Technology
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    • v.51 no.5
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    • pp.1398-1405
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    • 2019
  • We use a molecular dynamics simulation to explore thermal transport in oxide nuclear fuels with point defects. The effect of vacancy and substitutional defects on the thermal conductivity of plutonium dioxide and uranium dioxide is investigated. It is found that the thermal conductivities of these fuels are reduced significantly by the presence of small amount of vacancy defects; 0.1% oxygen vacancy reduces the thermal conductivity of plutonium dioxide by more than 10%. The missing of larger atoms has a more detrimental impact on the thermal conductivity of actinide oxides. In uranium dioxide, for example, 0.1% uranium vacancies decrease the thermal conductivity by 24.6% while the same concentration of oxygen vacancies decreases the thermal conductivity by 19.4%. However, uranium substitution has a minimal effect on the thermal conductivity; 1.0% uranium substitution decreases the thermal conductivity of plutonium dioxide only by 1.5%.

Modeling on thermal conductivity of MOX fuel considering its microstructural heterogeneity

  • Lee, Byung-Ho;Koo, Yang-Hyun;Sohn, Dong-Seong
    • Proceedings of the Korean Nuclear Society Conference
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    • pp.247-247
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    • 1999
  • This paper describes a new mechanistic thermal conductivity model considering the heterogeneous microstructure of MOX fuel. Even though the thermal conductivities of MOX have been investigated numerously by experimental measurements and theoretical analyses, they show the large scattering making the performance analysis of MOX fuel difficult. Therefore, a thermal conductivity model that depends on the heterogeneous microstructure of MOX fuel has been developed by using a general two-phase thermal conductivity model. In order to apply this model for developing the thermal conductivity for heterogeneous MOX fuel, the fuel is assumed to consist of Purich particles and U02 matrix including Pu02 in solid solution. Since little relevant data on Purich particles is available, FIGARO and SiemensKWU results are only used to characterize the microstructure of unirradiated and irradiated fuel. Philliponneaus and HALDEN models are selected for the local thermal conductivities for Purich particles and matrix, respectively. Then by combining the two models, overall thermal conductivity of MOX fuel is obtained. The new proposed model estimates the MOX thermal conductivity about 10% less than the value of U02 fuel, which is in the range of MOX thermal conductivity from HALDEN. The developed thermal conductivity model has been incorporated into KAERIs fuel performance code, COSMOS, and then verified using the measured data in the FIGARO program. Comparison of predicted and measured temperatures shows the reasonable agreement within acceptable error bounds together with satisfactory results for the fission gas release and gap pressure.essure.

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An Analytical Model for Predicting the Effective Thermal Conductivity of Woven Wire Wick Structure

  • Lee, Jin-Sung;Kim, Chul-Ju
    • International Journal of Air-Conditioning and Refrigeration
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    • v.10 no.2
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    • pp.72-78
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    • 2002
  • Woven wire wick is a very effective structure because of its easiness to insert inside of pipe for a miniature heat pipe. The present study was conducted to predict the porosity and the effective thermal conductivity of liquid-saturated woven wire wick. The porosity and the effective thermal conductivity of the evaporator region indicate different values from those of the condenser region due to the existence of non-flow region. The minimum value of the effective thermal conductivity indicates on condition of the $\theta$=$45^{Wcirc}$ and the values of the effective thermal conductivity increases symmetrically centering around the minimum value. The values of the effective thermal conductivity in the evaporator region at the angle of $45^{Wcirc}$ indicate about 60~80% higher than those in the condenser region for various combinations of copper, and stainless with water and ethanol.