• Title/Summary/Keyword: Tube conductivity

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Numerical Analysis of an Orifice Pulse Tube Refrigerator (오리피스 맥동관 냉동기의 수치적 해석)

  • Lee, K.S.;Jeong, E.S.;Choi, H.O.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.6 no.3
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    • pp.282-290
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    • 1994
  • A numerical model for the analysis and design of orifice pulse tube refrigerators has been developed. Heat transfer coefficient and friction factors in the model vary with time, and the real physical properties such as thermal conductivity and viscosity were used to improve the accuracy of the model. Thermodynamic behavior of the working fluid within pulse tube refrigerators was investigated and the effect of design parameters, such as reservoir volume, orifice diameter, and NTU of regenerator, on the cooling load and COP was shown.

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A Study on the Laminar Flow Field and Heat Transfer Coefficient Distribution for Supercritical Water in a Tube (초임계상태의 물에 대한 관 내 층류유동장 및 열전달계수 분포특성에 관한 연구)

  • 이상호
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.15 no.9
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    • pp.768-778
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    • 2003
  • Numerical analysis has been carried out to investigate laminar convective heat transfer in a tube for supercritical water near the thermodynamic critical point. Fluid flow and heat transfer are strongly coupled due to large variations of thermodynamic and transport properties such as density, specific heat, viscosity, and thermal conductivity near the critical point. Heat transfer characteristics in the developing region of the tube show transition behavior between liquid-like and gas-like phases with a peak in heat transfer coefficient distribution near the pseudocritical point. The peak of the heat transfer coefficient depends on pressure and wall heat flux rather than inlet temperature and Reynolds number, Results of the modeling provide convective heat transfer characteristics including velocity vectors, temperature, and the properties as well as the heat transfer coefficient. The effect of proximity to the critical point is considered and a heat transfer correlation is suggested for the peak of Nusselt number in the tube.

Analysis of electron beam landing shift of CRT by thermal radiative effect and thermal deformation (열 복사 효과와 열 변형을 고려한 CRT전자빔 오착 해석)

  • 강대진;김국원;송창섭
    • Journal of the Korean Institute of Telematics and Electronics C
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    • v.34C no.1
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    • pp.12-20
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    • 1997
  • In this paper, we analyze the thermal deformation of mask frame assembly using finite element method(FEM) and predict the beam landing shift during tube operation. For realistic analysis, the apparent thermal conductivity and the apparent elastic modulus are calculated and the shadow mask is modeled as shell without aperatures. Also, all parts inside the tube are modeled and the each radiative effect is considered. Then the finite element analysis is performed for transient thermo-elastic deformation of the mask frame assembly and the beam landing shift is calculated. Experiments are eprformed for 17" cathode ray tube (CRT) to validate the FEM analysis. The temperatures of all parts inside the tube and beam landing shift on the panel are measured and the results are discussed in comparison with the results of the FEM analysis.ysis.

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A Numerical Study on the Laminar Flow Field and Heat Transfer Coefficient Distribution for Supercritical Water in a Tube

  • Lee Sang-Ho
    • International Journal of Air-Conditioning and Refrigeration
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    • v.13 no.4
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    • pp.206-216
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    • 2005
  • Numerical analysis has been carried out to investigate laminar convective heat transfer at zero gravity in a tube for supercritical water near the thermodynamic critical point. Fluid flow and heat transfer are strongly coupled due to large variation of thermodynamic and transport properties such as density, specific heat, viscosity, and thermal conductivity near the critical point. Heat transfer characteristics in the developing region of the tube show transition behavior between liquid-like and gas-like phases with a peak in heat transfer coefficient distribution near the pseudo critical point. The peak of the heat transfer coefficient depends on pressure and wall heat flux rather than inlet temperature and Reynolds number. Results of the modeling provide convective heat transfer characteristics including velocity vectors, temperature, and the properties as well as the heat transfer coefficient. The effect of proximity on the critical point is considered and a heat transfer correlation is suggested for the peak of Nusselt number in the tube.

An Experimental Study on the Heat Transfer Characteristics of a Finned-Tube Heat Exchanger in a PCM Thermal Energy Storage System (상변화물질을 적용한 핀-관 열교환기의 열전달 성능 특성에 관한 실험적 연구)

  • Jung, Dong Il;Chang, Min;Kim, Yongchan
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.28 no.1
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    • pp.15-20
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    • 2016
  • Phase change materials (PCM) are able to store a large amount of latent heat, and can be applied to thermal energy storage systems. In a PCM, it takes a long time to store heat in the storage system because of the low thermal conductivity. In this study, a finned-tube-in-tank heat exchanger was applied to a PCM thermal energy storage system to increase heat transfer efficiency. The effects of geometric and operating parameters were investigated, and the results were compared with those of the tube-in-tank heat exchanger. The finned-tube-in-tank heat exchanger showed higher heat transfer effectiveness than the tube-in-tank heat exchanger. The heat exchange effectiveness of the storage tank was determined as a function of the average NTU.

A Study on Conductivity Characteristics of the Insulating Oil for X-ray Tube Housing (X선장치용(線裝置用) 절연유(絶緣油)의 도전특성(導電特性)에 관한 연구(硏究))

  • Kim, Young-Il;Lee, Duck-Chool;Chung, Yon-Tack
    • Journal of radiological science and technology
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    • v.9 no.1
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    • pp.73-81
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    • 1986
  • This paper carried out an experiment on the characteristics of time, temperature, electric field and the dependense of electrode materials and gap length by the conduction current of the insulating oil used for x-ray tube housing. The obtained results can be summarized as following: 1. In the x-ray tube housing insulating oil with vacuum condition, conduction current is declined more than the x-ray tube housing insultaing oil with the air, and is held stable states. 2. At the low electric field the higher temperature of the x-ray tube housing insulating oil is increased, the more conduction current. 3. The dependence of electrode material is appeared at the low electric field and the short gap length than the high and the long with Fe> Cu >Al. 4. At the I-E characteristics, the low electric field than 1000 [V/cm] is appeared Ohm's law region, and the high become saturation region. 5. At the same electric field, the longer gap length become, the more conduction current is increased, and the same applied voltage, the longer, the less conduction current is decreased, the less low than high temperature x-ray tube housing insulating oil.

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Increasing of Thermal Conductivity from Mixing of Additive on a Domestic Compacted Bentonite Buffer (국산 압축벤토나이트 완충재의 첨가제 혼합을 통한 열전도도 향상)

  • Lee, Jong-Pyo;Choi, Heui-Joo;Choi, Jong-Won;Lee, Minsoo
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.11 no.1
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    • pp.11-21
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    • 2013
  • The Geyoungju Ca-bentonite with dry density of 1.6 g/$cm^3$ has been considered as a standard buffer material for the disposal of high level waste in KAERI disposal system design. But it had relatively lower thermal conductivity compared with other surrounding materials, that was one of key parameters to limit the increase of the disposal density in the disposal system. In this study, various additives were selected and mixed with the Ca-bentonite in different mixing methods in order to increase the thermal conductivity from 0.8 W/mK to 1.0 W/mK. As an additive, CNT (Cabon Nano Tube), graphite, alumina, CuO, and $Fe_2O_3$ were selected, which are chemically stable and have good thermal conductivity. As mixing methods, dry hand-mixer mixing, wet milling and dry ball mill mixing were applied for the mixing. Above all, the ball mill mixing was proved to be most effective since the produced mixture was most homogeneous and showed higher increase in the thermal conductivity. From this study, it was confirmed that the thermal conductivity for the Geyoungju Ca-bentonite could be improved by adding small amount of highly thermal conductive material to 1.0 W/mk. In conclusion, it was believed that the experimental results will be valuable in the disposal system design if the additive effects on the swelling and permeability on the compact bentonite are also approved in further studies.

Theoretical study on electrical behavior of carbon chain inserted single-walled carbon nanotubes compared with Pt doped one

  • Cui, Hao;Zhang, Xiaoxing;Xiao, Hanyan;Tang, Ju
    • Carbon letters
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    • v.25
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    • pp.55-59
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    • 2018
  • Carbon chain inserted carbon nanotubes (CNTs) have been experimentally proven having undergone pronounced property change in terms of electrical conductivity compared with pure CNTs. This paper simulates the geometry of carbon chain inserted CNTs and analyzes the mechanism for conductivity change after insertion of carbon chain. The geometric simulation of Pt doped CNT was also implemented for comparison with the inserted one. The results indicate that both modification by Pt atom on the surface of CNT and addition of carbon chain in the channel of the tube are effective methods for transforming the electrical properties of the CNT, leading to the redistribution of electron and thereby causing the conductivity change in obtained configurations. All the calculations were obtained based on density functional theory method.

A Study on Heat Transfer Performance of Vertical Ground Heat Exchanger of GSHP(Ground Source Heat Pump) (GSHP용 수직형 지중열교환기의 열전달 성능에 관한 연구)

  • Chung, Min-Ho;Chang, Ki-Chang;Ra, Ho-Sang;Baik, Young-Jin;Park, Seong-Ryong;Yoo, Seong-Yeon
    • Proceedings of the KSME Conference
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    • 2007.05b
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    • pp.2102-2107
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    • 2007
  • GSHP systems are used for air-conditioning systems in commercial buildings, schools, and factories because of low operating and maintenance costs. These systems use the earth as a heat source in heating and a heat sink in cooling mode. Ground heat exchangers are classified by a horizontal and vertical type according to the installation method. Vertical type is usually constructed by placing small diameter high density polyethylene tube in a vertical borehole. Vertical tube sizes range from 20 to 40 mm nominal diameter. Borehole depth range between 100 and 200 m depending on local drilling conditions and available equipment. In this study, to evaluate the performance of single u-tube with bentonite grouting, single u-tube with broken stone grouting and double u-tube bentonite grouting of vertical ground heat exchangers, test sections are buried on the earth and experimental apparatus is installed. Therefore the heat transfer performance and pressure loss of these are estimated.

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A Study on Performance of Vertical Ground Heat Exchanger for Heat Pump (히트펌프용 수직형 지중열교환기의 성능에 관한 연구)

  • Chang, Ki-Chang;Chung, Min-Ho;Yoon, Hyung-Kee;Ra, Ho-Sang;Yoo, Seong-Yeon
    • 한국신재생에너지학회:학술대회논문집
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    • 2007.06a
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    • pp.466-469
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    • 2007
  • Heat pumps are used for air-conditioning systems in commercial buildings, schools, and factories because of low operating and maintenance costs. These systems use the earth as a heat source in heating mode and a heat sink in cooling mode. Ground heat exchangers are classified by a horizontal type and vertical type according to the installation method. A horizontal type means that a heat exchanger is laid in the trench bored in 1.2 to 1.8 m depth. And a vertical type is usually constructed by placing small diameter high density polyethylene tube in a vertical borehole. Vertical tube sizes range from 20 to 40 mm nominal diameter. Borehole depth range between 100 and 200 m depending on local drilling conditions and available equipment. In this study, to evaluate the performance of single u-tube with bentonite grouting, single u-tube with broken stone grouting and double n-tube bentonite grouting of vertical ground heat exchangers, test sections are buried on the earth and experimental apparatus is installed. Therefore the heat transfer performance and pressure loss of these are estimated.

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