• Title, Summary, Keyword: conductivity

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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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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.

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.

Evaluation of Hydraulic Conductivity Function in Unsaturated Soils using an Inverse Analysis (역해석기법을 이용한 불포화토 투수계수함수 산정에 관한 연구)

  • Lee, Joonyong;Han, Jin-Tae
    • Journal of The Korean Society of Agricultural Engineers
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    • v.55 no.4
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    • pp.1-11
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    • 2013
  • Unsaturated hydraulic conductivity function is one of key parameters to solve the flow phenomena in problems of landslide. Prediction models for hydraulic conductivity function related to soil-water retention curve equations in many geotechnical applications have been still used instead of direct measurement of the hydraulic conductivity function since prediction models from soil-water retention curve equations are attractive for their fast and easy use and low cost. However, many researchers found that prediction models for the hydraulic conductivity function can not predict the hydraulic conductivity exactly in comparison with experimental outputs. This research introduced an inverse analysis to evaluate the hydraulic conductivity function corresponding to experimental output from the flow pump system. Optimisation process was carried out to obtain the hydraulic conductivity function. This research showed that the inverse analysis with flow pump system was suitable to assess the hydraulic conductivity in unsaturated soil, and the prediction models for the hydraulic conductivity were led to the significant discrepancy from actual experimental outputs.

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.

Effect of Metal Powders on the Conductivity of Conductive Inks (금속입자가 전도성 잉크의 전도도에 미치는 영향)

  • Kwon, Doo-Hyo;Jeong, Tae-Eui;Kim, Nam-Soo;Han, Kenneth-N.
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.17 no.2
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    • pp.97-103
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    • 2008
  • In this investigation, conductivity of conductive inks was measured. A particular attention has been given to the effect of metal powders with various conductivity on the overall conductivity of the bulk ink. The conductivity of various solutions simulating conductive inks consisting of copper and silver was measured and the results have been discussed in relation to various applications of conductive inks in practice. A conductivity model simulating systems consisting of various materials has been introduced and the results were discussed. Materials of good conductivity are adversely affected by mixing with materials of poor conductivity simply through serial connection. However, parallel connection has rather little effect on the overall conductivity. The practical implication of various mixtures of materials on conductive inks has been discussed.

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.

Effect of W Particle Size on the Electrical and Thermal Conductivity of W-Cu Composites (W 입자크기가 W-Cu 복합재료의 전기 및 열전도도에 미치는 영향)

  • 양주환;오승탁;박상우;문인형
    • Journal of Korean Powder Metallurgy Institute
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    • v.11 no.1
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    • pp.43-49
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    • 2004
  • The electrical and thermal conductivity of W-Cu composites were investigated as a function of the W-particle size and W-W contiguity. Powder mixtures were prepared by ball milling or mechanical alloying process, and then sintered at various temperatures. The electrical conductivity of sintered composite was increased with decreasing W grain size. Dependence of electrical conductivity on the W grain size was explained by the W-W contiguity concept. The thermal conductivity was increased with increasing the temperature up to $600^{\circ}C$ but decreased at the temperature above $600^{\circ}C$ Also, thermal conductivity value was influenced by the W particle size. Change of thermal conductivity in W-Cu composites was discussed based on the observed microstructural characteristics and theoretical considerations.

Effect of open-core screw dislocation on axial conductivity in semiconductor crystals

  • Taira, Hisao;Sato, Motohiro
    • Advances in nano research
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    • v.1 no.3
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    • pp.171-182
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    • 2013
  • The alternating current (AC) conductivity in semiconductor crystals with an open-core screw dislocation is studied in the current work. The screw dislocation in crystalline media results in an effective potential field which affects the electronic transport properties of the system. Therefore, from a technological view point, it is interesting to investigate properties of AC conductivity at frequencies of a few terahertz. To quantify the screw-induced potential effect, we calculated the AC conductivity of dislocated crystals using the Kubo formula. The conductivity showed peaks within the terahertz frequency region, where the amplitude of the AC conductivity was large enough to be measured in experiments. The measurable conductivity peaks did not arise in dislocation-free crystals threaded by a magnetic flux tube. These results imply different conductivity mechanisms in crystals with a screw dislocation than those threaded by a magnetic flux tube, despite the apparent similarity in their electronic eigenstates.

Modified electrical conductivity test method for evaluation concrete permeability

  • Pilvar, Amirreza;Ramezanianpour, Ali Akbar;Rajaie, Hosein
    • Computers and Concrete
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    • v.16 no.6
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    • pp.865-880
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    • 2015
  • Standard test method for bulk electrical conductivity (ASTM C1760) provides a rapid indication of the concrete's resistance to the penetration of chloride ions by diffusion. In this paper a new approach for assessing the bulk electrical conductivity of saturated specimens of hardened concrete is presented. The test involves saturating concrete specimens with a 5 M NaCl solution before measuring the conductivity of the samples. By saturating specimens with a highly conductive solution, they showed virtually the same pore solution conductivity. Different concrete samples yield different conductivity primarily due to differences in their pore structure. The feasibility of the method has been demonstrated by testing different concrete mixtures consisting ordinary and blended cement of silica fume (SF) and calcined perlite powder (CPP). Two standard test methods of RCPT (ASTM C1202) and Bulk Conductivity (ASTM C1760) were also applied to all of the samples. The results show that for concretes containing SF and CPP, the proposed method is less sensitive towards the variations in the pore solution conductivity in comparison with RCPT and Bulk Conductivity tests. It seems that this method is suitable for the assessment of the performance and durability of different concretes containing supplementary cementitious materials.