• Title/Summary/Keyword: Effective thermal conductivity

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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.

Measurement of Effective Thermal Conductivity in Silica Gel Packed Bed (실리카겔 충전층에서의 유효열전도율 측정)

  • Kwon Oh-Kyung;Yun Jae-Ho;Kim Joung-Ha
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.16 no.12
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    • pp.1126-1133
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    • 2004
  • This paper presents an experimental measurement of effective thermal conductivity in an adsorbent packed bed with silica gel A type. The effective thermal conductivity was measured under different conditions of the adsorbent bed temperature, pressure, particle size and water content by using the transient hot wire method. The measured effective thermal conductivity showed to become bigger with decreasing particle size or increasing water content, but it was a little affected with increasing bed temperature and pressure. The bed temperature was varied in the range of 1$0^{\circ}C$ (equation omitted) T (equation omitted) 5$0^{\circ}C$ and the pressure in the range of 10 kPa (equation omitted) P (equation omitted) 190 kPa. The results show that 0.10~0.18 W/mㆍK of effective thermal conductivity measured for the zero water content.

Effect of packing structure on anisotropic effective thermal conductivity of thin ceramic pebble bed

  • Wang, Shuang;Wang, Shuai;Wu, Bowen;Lu, Yuelin;Zhang, Kefan;Chen, Hongli
    • Nuclear Engineering and Technology
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    • v.53 no.7
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    • pp.2174-2183
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    • 2021
  • Helium cooled solid breeder blanket as an important blanket candidate of the Tokamak fusion reactor uses ceramic pebble bed for tritium breeding. Considering the poor effective thermal conductivity of the ceramic breeder pebble bed, thin structure of tritium breeder pebble bed is usually adopted in the blanket design. The container wall has a great influence on the thin pebble bed packing structure, especially for the assembly of mono-sized particles, and thin pebble bed will appear anisotropic effective thermal conductivity phenomenon. In this paper, thin ceramic pebble beds composed of 1 mm diameter Li4SiO4 particles are generated by the EDEM 2.7. The effective thermal conductivity of different thickness pebble beds in the three-dimensional directions are analyzed by three-dimensional thermal network method. It is observed that thin Li4SiO4 pebble bed showing anisotropic effective thermal conductivity under the practical design size. Normally, the effective thermal conductivity along the bed vertical direction is higher than the horizontal direction due to the gravity effect. As the thickness increases from 10 mm to 40 mm, the effective thermal conductivity of the pebble bed gradually increases.

The effects of particle shape on the effective thermal conductivity enhancement of nanofluids (나노유체 입자상 모양의 유효 열전도도에의 영향)

  • Koo, June-Mo;Kang, Yong-Tae
    • Proceedings of the KSME Conference
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    • pp.2106-2109
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    • 2008
  • Nanofluids have been studied as possible alternatives for heat transfer fluids to improve the efficiency of heat exchangers. There are deviations of measured effective thermal conductivities between research-groups, and the mechanisms of the effective thermal conductivity enhancement of nanofluids are not confirmed yet. In this study, the effects of particle shape on the effective thermal conductivity enhancement are discussed and presented as a possible explanation of the deviations. The particle motion effect is found to be negligible for nanofluids of high aspect ratio cylindrical particles, which is believed to be important for nanofluids of spherical particles, while the percolation network formation and contact resistance play dominant roles in determining the effective thermal conductivity.

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Effect of Some Parameters on Ground Effective Thermal Conductivity (지중열교환기 설치 조건이 지중 유효 열전도도에 미치는 영향)

  • Choi, Jae-Ho;Lim, Hyo-Jae;Kong, Hyoung-Jin;Sohn, Byong-Hu
    • Proceedings of the SAREK Conference
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    • pp.33-38
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    • 2008
  • A ground-loop heat exchanger in a ground source heat pump system is an important unit that determines the thermal performance of a system and its initial cost. The Size and performance of this heat exchanger is highly dependent on ground thermal properties. A proper design requires certain site-specific parameters, most importantly the ground effective thermal conductivity, the borehole thermal resistance and the undisturbed ground temperature. This study was performed to investigate the effect of some parameters such as borehole lengths, various grouting materials and U-tube configurations on ground effective thermal conductivity. In this study, thermal response tests were conducted using a testing device with 9-different ground-loop heat exchangers. From the experimental results, the length of ground-loop heat exchanger affects to the effective thermal conductivity. Among the various grouting materials, the bentonite-based grout with silica sand shows the largest thermal conductivity value.

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Construction of Ground Effective Thermal Conductivity Database for Design of Closed-Loop Ground Heat Exchangers (밀폐형 지중열교환기 설계를 위한 지중 유효열전도도 데이터베이스 구축)

  • Choi, Jae-Ho;Sohn, Byong-Hu;Lim, Hyo-Jae
    • Proceedings of the SAREK Conference
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    • pp.776-781
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    • 2008
  • A ground heat exchanger in a GSHP system is an important unit that determines the thermal performance of a system and its initial cost. The Size and performance of this heat exchanger is highly dependent on the thermal properties. A proper design requires certain site-specific parameters, most importantly the ground effective thermal conductivity, the borehole thermal resistance and the undisturbed ground temperature. This paper is part of a research project aiming at constructing a database of these site-specific properties, especially ground effective thermal conductivity. The objective was to develop and evaluation method, and to provide this knowledge to design engineers. To achieve these goals, thermal response tests were conducted using a testing device at nearly 150 locations in Korea. The in-situ thermal response is the temperature development over time when a known heating load imposed, e.g. by circulating a heat carrier fluid through the test exchangers. The line-source model was then applied to the response test data because of its simplicity. From the data analysis, the range of ground effective thermal conductivity at various sites is $1.5{\sim}4.0\;W$/mK. The results also show that the ground effective thermal conductivity varies with grouting materials as well as regional geological conditions and groundwater flow.

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A Study on the Evaluation of Pressure Resistance and Effective Thermal Conductivity of Thin Heat Pipes Using Polymer Compound Sheets for Bonding Metal Thin Plates (금속박판 접합용 고분자화합물시트를 이용한 박형 히트파이프 내압성 및 유효열전도율 평가에 관한 연구)

  • Yu, Byeong-Seok;Kim, Jeong-Hun;Kim, Dong-Gyu
    • Journal of the Korean Society of Industry Convergence
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    • v.24 no.4_2
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    • pp.509-515
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    • 2021
  • In this study, a pressure vessel for a heat pipe was fabricated by bonding a metal thin film using a polymer compound sheet. In order to confirm the applicability of the experimentally manufactured copper material thin heat pipe of 0.6 mm or less, the pressure resistance and effective thermal conductivity for pressure generated according to the type of the working fluid of the heat pipe were evaluated to suggest the commercialization potential of the thin heat pipe. As a result of evaluating the pressure resistance and effective thermal conductivity performance of the thin heat pipe, the following conclusions were drawn. 1) Using a PEEK-based polymer compound sheet, it was possible to fabricate a pressure vessel for a thin heat pipe with a pressure resistance of up to 1.0 MPa by bonding a copper thin film, and the possibility of commercialization was confirmed at a temperature below 120 ℃. 2) In the case of the effective thermal conductivity performance evaluation test, the effective thermal conductivity of ethanol was higher than that of FC72 and Novec7000, and in the case of ethanol, the maximum effective thermal conductivity was 2,851 W/mK at 3.0 W of heating.

The Effects of the Installation Conditions of Ground Loop Heat Exchanger to the Thermal Conductivity and Borehole Resistance (지중열교환기 설치 조건이 지중 유효 열전도도와 보어홀 열저항에 미치는 영향)

  • Lim, Hyo-Jae;Kong, Hyoung-Jin;Kang, Sung-Jae;Choi, Jae-Ho
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.23 no.2
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    • pp.95-102
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    • 2011
  • A ground loop heat exchanger in a ground source heat pump system is an important unit that determines the thermal performance of a system and its initial cost. A proper design requires certain site specific parameters, most importantly the ground effective thermal conductivity, the borehole thermal resistance and the undisturbed ground temperature. This study was performed to investigate the effect of some parameters such as borehole lengths, various grouting materials and U tube configurations on ground effective thermal conductivity and borehole thermal resistance. In this study, thermal response tests were conducted using a testing device to 9 different ground loop heat exchangers. From the experimental results, the length of ground loop heat exchanger affects to the effective thermal conductivity. The results of this experiment shows that higher thermal conductivity of grouting materials leads to the increase effective thermal conductivity from 22 to 32%. Also, mounting spacers have increased by 14%.

Measurement of the Effective Thermal Conductivity of Porous Media in the Mockup Apparatus of Reactor Vessel (원자로 모의 다공질 매체의 유효 열전달 계수 측정)

  • 김용균;황종선;이용범;최석기;남호윤
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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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.

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Heat transfer enhancement of metal hydride $(Mm(La_{0.6-0.8})Ni_{4.0}Co_{0.6}Mn_{0.2}Al_{0.2})$ for hydrogen storage (수소저장용 금속수소화물$(Mm(La_{0.6-0.8})Ni_{4.0}Co_{0.6}Mn_{0.2}Al_{0.2})$의 전열촉진)

  • Bae Sang-Chul;Yang Yang;Masanori Monde
    • New & Renewable Energy
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    • v.2 no.2
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    • pp.75-80
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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 0.99 wt% of carbon fiber. This is a good result comparing to other method which can reach higher effective thermal conductivity but needs much higher mass fraction of additives too.

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