• Title/Summary/Keyword: Effective thermal conductivity

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A Model for Predicting Effective Thermal Conductivity of 2- or 3- Component Sand System (모래의 2 또는 3성분계의 유효열전도도 예측 모델)

  • Park, Sang Il;Hartley, James G.
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.7
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    • pp.811-819
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    • 1999
  • A theoretical model to predict the effective thermal conductivity of sands Is developed by considering the participating heat transfer mechanisms and their relationship to the model geometry. Comparison between the calculations and the measurements indicates that the assumptions to introduce two model constants (${\phi}_{af}$ and ${\delta}$) for model development were justified. As a results, the model was proved to predict the effective thermal conductivities of 2- and 3-component systems of two silica sands saturated with fluids or bonded with liquid binders in a reasonable accuracy.

Measurement of the Shear Rate-Dependent Thermal Conductivity for Suspension with Microparticles (미립자를 포함한 현탁액의 전단율에 의존적인 열전도율 측정)

  • Lee, Sung-Hyuk;Shin, Sehyun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.22 no.8
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    • pp.1141-1151
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    • 1998
  • An effective thermal conductivity measurement for suspensions of microparticles in oil mixture is conducted in order to evaluate the shear rate-dependence of the thermal conductivity of suspensions. Measurements are made for rotating Couette flows between two concentric cylinders. The rotating outer cylinder is immersed into a constant temperature water bath while the stationary inner cylinder is subject to a uniform heat fluff. Test fluids are made to be homogeneous suspensions, in which neutrally buoyant microparticles ($d=25{\sim}300{\mu}m$) are uniformly dispersed. The present measurements show strong shear-rate dependent thermal conductivities for the suspensions, which are higher than those at zero shear rate. The shear rate dependent thermal conductivity increases with the particle size and volume concentration.4 new model for shear rate-dependent thermal conductivity of microparticle suspensions is proposed; the correlation covers from zero shear rate value to asymptotic plateau value at moderately high shear rates.

An Experimental Study on the Performance of Semi-Closed Loop Ground Heat Exchanger (반밀폐형 지중열교환기 성능에 관한 실험적 연구)

  • Kim, Ook-Joong;Yeom, Han-Kil;Lee, Chun-Woo
    • 한국신재생에너지학회:학술대회논문집
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    • 2007.11a
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    • pp.542-545
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    • 2007
  • A semi-closed loop ground heat exchanger is proposed and its performance is compared through the measuring the effective thermal conductivity of the ground. In-situ tests based on the line source model are carried out to evaluate the thermal characteristics of each ground heat exchanger which has different penetration water flow rate. The test results show the increasing effective thermal conductivity of ground as the penetration water flow rate(PWFR) is increased. Therefore, the higher thermal performance of the proposed semi-closed ground heat exchanger can be expected.

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Thermophysical Properties of the Soybean Curd and Prediction of its Thermal Conductivity 2. The 'intrinsic' thermal conductivity of soybean protein and prediction of the thermal conductivity of soybean curd (두부의 전열물성 및 유효열전도도의 추정 2. 대두단상질의 고유열전도도 측정과 두부의 유효열전도도의 추정)

  • KONG Jai-Yul
    • Korean Journal of Fisheries and Aquatic Sciences
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    • v.15 no.3
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    • pp.219-225
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    • 1982
  • Four heat conduction models were examined for defatted soy-protein curds in order to get the 'intrinsic' thermal conductivity of soy-protein. As the result of examination, the 'intrinsic', thermal conductivities of soy-protein, frozen and unfrozen states, were determined on the basis of series model to be 0.488 W/m.K and 0.300 W/m.K, respectively. By using the 'intrinsic' thermal conductivity values of soybean protein and the series model, the effective thermal conductivity of soybean curds, with and without fat, at frozen and unfrozen states, was predicted satisfactorily, The temperature dependency of the effective thermal conductivity of soybean curd was mostly observed to correlate with the thermal conductivity of water and ice.

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STUDY ON A EFFECTIVE THERMAL CONDUCTIVITY OF THE CFRP COMPOSITE STRUCTURE BY A SIMPLIFIED MODEL (모델 단순화에 의한 CFRP 복합 구조물의 유효 열전도율 추출 방법 연구)

  • Kim, D.G.;Han, K.I.;Choi, J.H.;Lee, J.J.;Kim, T.K.
    • Journal of computational fluids engineering
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    • v.20 no.4
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    • pp.63-69
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    • 2015
  • The thermal balance test in vacuum chamber for satellite structures is an essential step in the process of satellite development. However, it is technically and economically difficult to fully replicate the space environment by using the vacuum chamber. To overcome these limitations, the thermal analysis through a computer simulation technique has been conducted. The CFRP composite material has attracted attention as satellite structures since it has advantages of excellent mechanical properties and light weight. However, the nonuniform nature of the thermal conductivity of the CFRP structure should be noted at the step of thermal analysis of the satellite. Two different approaches are studied for the thermal analyses; a detailed numerical modeling and a simplified model expressed by an effective thermal conductivity. In this paper, the effective thermal conductivities of the CFRP composite structures are extracted from the detailed numerical results to provide a practical thermal design data for the satellite fabricated with the CFRP composite structure. Calculation results of the surface temperature and the thermal conductivities along x, y, z directions show fairly good agreements between the detailed modeling and the simplified model for all the cases studied here.

Measuring Thermal Conductivity of Nanofluids and Heat Transfer Enhancement (나노유체의 열전도율 측정과 열전달 향상)

  • Lee, Shin-Pyo;Choi, Cheol;Oh, Je-Myung
    • 유체기계공업학회:학술대회논문집
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    • 2006.08a
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    • pp.147-150
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    • 2006
  • A new class of heat transfer fluid with higher thermal conductivity, called nanofluids has been developed by Dr. S. Choi about decade ago. Many exciting experimental and theoretical results have been reported worldwide to predict the thermal conductivity enhancement of nanofluids, however, they sometimes show excessive large discrepancies between each other. This kind of disagreements in thermal conductivity data is partly ascribable to the accuracy of the measuring apparatus, that is, mostly used THM(transient hot-wire method). New thermal conductivity measuring method whose principle is different from that of conventional THM is proposed in this article and measurements and uncertainty analysis were made for the three nanofluid samples with different particle concentration of pure, 2% and 4% of AlN nanofluids.

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An Experimental Study on the Thermal Performance Measurement of Standing Column Well type Borehole Heat Exchanger (스탠딩컬럼웰형(SCW) 지중열교환기의 열성능 측정에 관한 실험적 연구)

  • Lee, Sanghoon;Choe, Yongseok;An, Kunmuk
    • 한국신재생에너지학회:학술대회논문집
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    • 2010.11a
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    • pp.122.2-122.2
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    • 2010
  • Knowledge of ground thermal properties is most important for the proper design of BHE(borehole heat exchanger) systems. The configure type, pipe size and thermal performance of the BHE is highly dependent on the ground source heatpump system-efficiency and instruction cost. Thermal response tests with mobile measurement devices were developed primarily for in-situ determination of design data for Standing Column Well apply. The main purpose has been to determine in-situ values of effective ground thermal conductivity and thermal resistance, including the effect of ground-water flow and natural convection in the boreholes. The test rig is set up on a some trailer, and contains a sub-circulation pump, a boiler, temperature sensors, flow meter and a data logger for recording the temperature and circulation fluid flow data. A constant heating power is injected into the SCW through the test rig and the resulting temperature change in the SCW is recorded. The recorded temperature data are analysed with a line-source model, which gives the effective in-situ values of rock thermal conductivity and thermal resistance of SCW.

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An Experimental Study on the Thermal Performance Measurement of Large Diameter Borehole Heat Exchanger(LD-BHE) for Tripe-U Pipes Spacer Apply (3중관용 스페이서를 적용한 대구경 지중열교환기의 성능측정에 관한 연구)

  • Lee, Sang-Hoon;Park, Jong-Woo;Lim, Kyoung-Bin
    • 한국신재생에너지학회:학술대회논문집
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    • 2009.11a
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    • pp.581-586
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    • 2009
  • Knowledge of ground thermal properties is most important for the proper design of large scale BHE(borehole heat exchanger) systems. The type, pipe size and thermal performance of the BHE is highly dependent on the ground source heatpump system-efficiency and instruction cost. Thermal response tests with mobile measurement devices were developed primarily for insitu determination of design data for large diameter BHE for triple-U spacer apply. The main purpose has been to determine insitu values of effective ground thermal conductivity and thermal resistance, including the effect of ground-water flow and natural convection in the boreholes. The test rig is set up on a some trailer, and contains a circulation pump, a inline heater, temperature sensors, flow meter, power analysis meter and a data logger for recording the temperature, fluid flow data. A constant heat power is injected into the borehole through the tripl-U pipes system of test rig and the resulting temperature change in the borehole is recorded. The recorded temperature data are analysed with a line-source model, which gives the effective insitu values of rock thermal conductivity and borehole thermal resistance of large diameter BHE for spacer apply.

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Assessment of the Models for Predicting the Thermal Conductivity of Saturated Kaolinite (포화된 카올리나이트를 이용한 열전도계수 예측모델의 신뢰성 검토)

  • Lee, Jangguen;Kim, Hakseung;Kang, Jaemo;Kim, Youngseok;Bae, Gyujin
    • Journal of the Korean GEO-environmental Society
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    • v.13 no.3
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    • pp.21-27
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    • 2012
  • Estimating the thermal conductivity of clayey soils is important for enhancing the performance of geoengineering structures in cold regions and clay barriers for nuclear waste repositories, but specimen disturbance, saturation, and heat boundary conditions of the test apparatus hinder reliable measurements of the thermal conductivity of saturated clayey soils. This paper presents the results of an experimental study carried out using modified consolidation tests with the needle probe method to measure thermal conductivity. Experimental consolidation tests with saturated kaolinite were performed to investigate the effect of effective stress and dry density on thermal conductivity for saturated kaolinite. In addition, thermal conductivity of soil particles were thoroughly investigated and experimental results were used to evaluate the accuracy of the models to predict thermal conductivity.

Limitations and improvement of the in situ measurements of ground thermal conductivity in Korea (국내 지중열전도도 측정 방법의 한계 및 개선 방향)

  • Shim, Byoung Ohan
    • 한국신재생에너지학회:학술대회논문집
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    • 2011.05a
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    • pp.195.2-195.2
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    • 2011
  • The borehole heat exchanger of Geothermal Heat Pump (GHP) system should be sustainable and cost effective for long term operation. To guaranty the performance of the system thermal Response Tests (TRTs) with simple recommended procedures have been applied in many countries. Korea government developed a standard TRT procedure in order to control the quality on GHP projects. In the TRT procedure interpretation method has a rule that data set has to be interpreted by the line source model(LSM). The LSM employes some assumptions that surrounding medium is homogeneous and the line source is infinite and constant heat flux, however real ground condition is unisotropic and heterogeneous, and showing regional or local ground water flows in many cases. We need to develope improved evaluation models to estimate accurate ground thermal conductivity with respect to geological and influence of ground water because current TRT standard test procedure has limitations to be applied for every locations and system. This study surveyed the uncertainty of the thermal parameters from the interpretation method considering different evaluation period. The interpretation of 208 TRT data sets represents limitations of LSM application that some obtained ground thermal conductivities are statistically unstable and convergence time of ground thermal conductivity over test period shows trends responding the length of test period. This evaluation study will be helpful to provide some effective procedure for the thermal parameter estimation and to complement current TRT standard procedure.

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