• Title/Summary/Keyword: Tube conductivity

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Thermal Performance of the Bubble Jet Loop Heat Pipe Using Eccentric Heater in Evaporating Section (증발부에 편심 가열부를 사용한 버블젯 루프 히트파이프의 열성능)

  • Kim, Jong-Soo;Kim, Sung-Bok
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.27 no.12
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    • pp.652-658
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    • 2015
  • The Bubble Jet Loop Heat Pipe (BJLHP) is designed to operate in the horizontal orientation. The motion of the bubble generated by boiling working fluid on a heater surface in the evaporating section of the BJLHP helps the working fluid transfer heat to the condensing portion. In this study, we changed the position of the heater in the evaporating section from concentric to eccentric. The concentric heater is located at the center of the tube in the evaporating part, and the eccentric heater is located at the bottom of the inner surface of the same tube. We used R-134a as the working fluid, and the charging ratio was 50%vol. We measured the temperatures of the evaporating and condensing sections by changing the input electric power from 50 W to 200 W, measuring every 50 W. The results of the experiment show that the effective thermal conductivity of BJLHP using an eccentric heater is four times higher than the BJLHP obtained using a concentric heater. Additionally, we conducted a visualization experiment on the evaporating portion of BJLHP to determine why the effective thermal conductivity was higher. The working fluid was water, and we took pictures of the flow visualization for BJLHP. Nucleate boiling with the eccentric heater was more intense and generated more bubbles. Therefore, the eccentric heater was more saturated by the liquefied working fluid.

Modification of Hydrogen Determinator for Total Hydrogen Analysis in Irradiated Zircaloy Cladding Tube (수소분석기 개조 및 조사후 지르칼로이 피복관의 총수소분석)

  • Park, Soon-Dal;Choi, Kwang-Soon;Kim, Jong-Goo;Joe, Kih-Soo;Kim, Won-Ho
    • Analytical Science and Technology
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    • v.12 no.6
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    • pp.490-497
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    • 1999
  • A hydrogen determinator was modified and installed in the glove box to analyse total hydrogen content in irradiated zircaloy tube. The analysis method of hydrogen is Inert Gas Fusion(IGF)-Thermal Conductivity Detection(TCD). The hydrogen recoveries of no tin method using Ti and Zr matrix standards, respectively, were available within $3{\mu}g$ of hydrogen. Also the smaller size of sample showed the better hydrogen recovery. It was found that the hydrogen standard of Ti matrix is avaliable to hydrogen analysis in zircaloy sample. The mean radioactivity of irradiated zircaloy sample was 10 mR/hr and hydrogen concentration was 130 ppm.

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Sensitivity Analysis on Design Factor of Ground Heat Exchanger for Optimum Design of Vertical Ground Source Heat Pump System (수직밀폐형 지중열교환기의 최적설계를 위한 설계인자 영향도 분석)

  • Bae, Sangmu;Kim, Hongkyo;Nam, Yujin
    • Journal of the Architectural Institute of Korea Structure & Construction
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    • v.34 no.3
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    • pp.87-93
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    • 2018
  • Ground source heat pump(GSHP) system is one of the high efficiency heat source systems which utilizes the constant geothermal energy of a underground water or soil. However, the design of conventional GSHP system in the domestic market is dependent on the experience of the designer and the installer, and it causes increase of initial installation cost or degradation of system performance. Therefore, it is necessary to develop a guideline and the optimal design method to maintain stable performance of the system and reduce installation cost. In this study, in order to optimize the GSHP system, design factors according to ground heat exchanger(GHX) type have been examine by simulation tool. Furthermore, the design factors and the correlation of a single U-tube and a double U-tube were analyzed quantitatively through sensitivity analysis. Results indicated that, the length of the ground heat exchanger was greatly influenced by grout thermal conductivity for single U-tube and pipe spacing for double U-tube.

Effect of Multi-wall Carbon Nanotube Surface Treatment on the Interface and Thermal Conductivity of Carbon Nanotube-based Composites (다중벽탄소나노튜브 복합재료의 계면 및 열전도도에 표면처리 방법이 미치는 영향)

  • Yoo, Gi-Moon;Lee, Sung-Goo;Kim, Sung-Ryong
    • Journal of Adhesion and Interface
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    • v.11 no.4
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    • pp.174-180
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    • 2010
  • The effect of carbon nanotube surface treatment on the interface and thermal conductivity of carbon nanotube-based poly(methylmethacrylate) (PMMA) composites was investigated. Coagulation and atomic-transfer radical polymerization (ATRP) was applied to modify the surface of multi-wall carbon nano-tube. The composite of ATRP method used carbon nanotube showed the higher transparency and thermal conductivities than that of the coagulation method used. In comparison to the thermal conductivity of pure PMMA, 0.21 W/mK, the ATRP carbon nanotube used PMMA/MWNT composite showed a thermal conductivity of 0.38 W/mK. The interface between carbon nanotube and PMMA was observed by scanning electron microscope and uniform dispersion of carbon nanotube was observed without any void in the PMMA matrix. It may be beneficial to transport the phonon without any scattering and it may result in a higher thermal conductivity.

Natural Convection in the Annulus between a Horizontal Conducting Tube and a Cylinder with Spacers (수평전도관(水平傳導管)과 원통(圓筒)사이에 격판(隔板)을 가진 환상공간(環狀空間)에서의 자연대류(自然對流))

  • Lee, Sang-Hoon;Lee, Bum-Chul;Kwon, Sun-Sok
    • Solar Energy
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    • v.7 no.2
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    • pp.86-97
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    • 1987
  • Natural convection in the annulus between a horizontal conducting tube and a cylinder with spacers has been studied by 2-dimensional numerical method with finite difference techniques. The effects of Rayleigh number, conductivities of conducting tube and spacer, and position of spacers were studied analytically. In case of vertical spacers, the maximum local Nusselt number appears at ${\theta}{\approx}50^{\circ}$ in a conducting tube and ${\theta}{\approx}30^{\circ}$ in an outer cylinder, The local Nusselt numbers show positive values on the lower spacer, but negative values on the surface of the upper spacer. In case of horizontal spacers, the flow over the spacer is more active than that of under the spacer as the Rayleigh number increases. The maximum local Nusselt appeares at ${\theta}=180^{\circ}$ in a conducting tube and at ${\theta}=0^{\circ}$ in an outer cylinder. The local Nusselt numbers show positive values on the upward surface, but negative values on the downward surface of spacer. As the dimensionless conductivity increases, the mean Nusselt number remarkably increases at $K_w/K_f<48$ and show almost even at $K_w/K_f{\ge}48$. The mean Nusselt number of a conducting tube with vertical spacers is 5.12 percent less and with horizontal spacers is 11.33 percent less than that of a conducting tube without spacer at $Ra=10^4$, Pr = 0.7 and $K_w/K_f=48$.

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Characterization of Microstructure and Thermal property of Ash Deposits on Fire-side Boiler Tube

  • Bang, Jung Won;Lee, Yoon-Joo;Shin, Dong-Geun;Kim, Younghee;Kim, Soo-Ryong;Baek, Chul-Seoung;Kwon, Woo-Teck
    • Journal of the Korean Ceramic Society
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    • v.53 no.6
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    • pp.659-664
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    • 2016
  • Ash deposition of heat exchange boiler, caused mainly by accumulation of particulate matter, reduces heat transfer of the boiler system. Heat and mass transfer through porous media such as ash deposits mainly depend on the microstructure of deposited ash. Therefore, in this study, we investigated microstructural and thermal properties of the ash deposited on the boiler tube. Samples for this research were obtained from the fuel economizer tube in an industrial waste incinerator. To characterize microstructures of the ash deposit samples, scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD) and BET analysis were employed. The results revealed that it had a porous structure with small particles mostly of less than a few micrometers; the contents of Ca and S were 19.3, 22.6% and 18.5, 18.7%, respectively. Also, the results showed that it consisted mainly of anhydrite ($CaSO_4$) crystals. - The thermal conductivities of the ash deposit sample obtained from the economizer tube in industrial waste incinerator were measured to be 0.63 and 0.54 W/mK at $200^{\circ}C$, which were about 100 times less than the thermal conductivity (61.32 W/mK) of the boiler tube itself, indicating that ash deposition on the boiler tube was closely related to a decrease in boiler heat transfer.

A study on the heat recovery Characteristics of double tube type heat recovery ventilation system by double pipe material (이중관 재질에 따른 이중관형 열회수 환기장치의 열회수 특성 연구)

  • Kim, Eun-Young;Cho, Jin-Pyo
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.18 no.4
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    • pp.21-26
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    • 2017
  • In this study, performance tests were conducted to investigate the applicability of a double-tube heat recovery ventilation system. Paper, aluminum, polymer, were investigated as materials for the inner tube using the same exhaust-air volume. In all cases, the temperature exchange efficiency of the aluminum tube was the highest, while the paper tube showed similar results to those of the polymer tube. This probably resulted from the differences in thermal conductivity and thicknesses of the materials. The humidity exchange efficiency was the highest for the paper tubes in all cases, while the aluminum tubes and polymer tubes showed similar results. The total heat exchange efficiency, which includes the values of humidity exchange and temperature exchange, was highest in the case of the paper tube, and the aluminum tube and the polymer tube showed similar results. In the case of the paper tube, sensible heat and latent heat exchange occur at the same time, and the coefficient of energy of the aluminum tube and polymer tube are large values, when to be compared with only applicably sensible heat exchange coefficient of the aluminum tube and the polymer tube of total heat exchange efficiency value. The results of this study could be applied to the design of a ventilation system.

Graphitic Mesostructured Carbon from an Aliphatic Hydrocarbon Precursor

  • Kim, Chy-Hyung;Oh, Teresa
    • Bulletin of the Korean Chemical Society
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    • v.30 no.9
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    • pp.1978-1980
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    • 2009
  • A mesostructured form of carbon was fabricated from a template of mesostructured silica by using pentane, an aliphatic hydrocarbon precursor. To synthesize the mesostructured silica, a buffered (pH of 6.5) mixture of nonionic Pluronic P123 surfactant, sodium silicate, and acetic acid were used. The impregnated silica with Fe$(CO)_5$ (wt 5%) and pentane was placed in a quartz tube, treated with pentane vapor at 800 ${^{\circ}C}$ for two hours to synthesize the mesostructured carbon. The XRD patterns of the carbon replica in the low/wide angle regions, its TEM images, and nitrogen adsorption-desorption isotherm revealed that the long-range framework order of mesostructure with the pore size centered on 2.8 nm was maintained to some extent mainly due to some portions of mesophase carbon that work as a support to fix the hexagonal frameworks by anchoring on the pore surface with an improved graphitic character. The dc conductivity of the mesostructured carbon in pressed powder form at 6.0 MPa was 2.08 S/cm.

Effects of Soil and Air Flow Characteristics on the Soil-Air Heat Exchanger Performances (토양과 공기유동특성이 토양-공기 열교환기 성능에 미치는 영향)

  • 김영복;김기영
    • Journal of Biosystems Engineering
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    • v.23 no.1
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    • pp.21-30
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    • 1998
  • A theoretical model was developed to evaluate the effects of soil and airflow characteristics on the soil-air heat exchanger performances. The model, which includes three-dimensional transient energy and mass equilibrium-equation, was solved by using a computer program that uses Finite Difference Methods and Gauss-Seidel iteration computation. Energy gains, heat exchange efficiencies, and outlet air temperature are presented including the effects of soil moisture content, soil conductivity, soil thermal diffusivity, and soil initial temperature. Also, data related to the effects of airflow rate and inlet air temperature on the thermal performance of the system are presented. The results indicated that energy gains depend on soil conductivity, soil thermal diffusivity, and soil initial temperature. Heat exchange efficiencies relied on air mass flow rate and soil moisture content.

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Study on Characteristics of Plasma in Hollow Cathode Discharge (Hollow Cathode Discharge에서 플라즈마 특성에 관한 연구)

  • Yoon, Man-Young;Shin, Jong-Soon
    • Journal of the Korean Graphic Arts Communication Society
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    • v.23 no.2
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    • pp.93-101
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    • 2005
  • The measured plasma temperature of Ar hollow cathode discharge for several metal cathodes are about $620\;{\sim}\;780K$ at discharge current of $7\;{\sim}\;10mA$. The optogalvanic signals were measured using hollow cathode discharge tube with argon as buffer gas at change of discharge currents. A change of ionization rate due to electron collision causes an increase or decrease of the electric conductivity. This change in electric conductivity generates the optogalvanic signal. We conclude that optogalvanic signal has close relation with the lowest metastable atoms density at low current.

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