• 제목/요약/키워드: Tube conductivity

검색결과 161건 처리시간 0.021초

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

  • 이강선;정은수;최헌오
    • 설비공학논문집
    • /
    • 제6권3호
    • /
    • pp.282-290
    • /
    • 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.

  • PDF

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

  • 이상호
    • 설비공학논문집
    • /
    • 제15권9호
    • /
    • pp.768-778
    • /
    • 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.

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

  • 강대진;김국원;송창섭
    • 전자공학회논문지C
    • /
    • 제34C권1호
    • /
    • pp.12-20
    • /
    • 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.

  • PDF

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
    • /
    • 제13권4호
    • /
    • pp.206-216
    • /
    • 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.

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

  • 정동일;장민;김용찬
    • 설비공학논문집
    • /
    • 제28권1호
    • /
    • pp.15-20
    • /
    • 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.

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

  • 김영일;이덕출;정연택
    • 대한방사선기술학회지:방사선기술과학
    • /
    • 제9권1호
    • /
    • pp.73-81
    • /
    • 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.

  • PDF

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

  • 이종표;최희주;최종원;이민수
    • 방사성폐기물학회지
    • /
    • 제11권1호
    • /
    • pp.11-21
    • /
    • 2013
  • 현재 고준위 방사성 폐기물 심층 처분 시스템에서 기본 완충재 물질로서 건조밀도 1.6 g/$cm^3$의 경주산 칼슘 벤토나이트를 사용하고 있으나, 열전도도가 낮은 단점이 있다. 따라서 본 연구에서는 기준 완충재의 열전도율을 0.8 W/mK에서 1.0 W/mK로 향상시키기 위한 목적으로 다양한 첨가제를 다양한 혼합 방법을 통해 배합하고 열전도도를 측정하였다. 첨가제는 CNT(Cabon Nano Tube), Graphite, Alumina, CuO 및 $Fe_2O_3$ 등을 사용하였다. 혼합 방법의 경우, 핸드 믹서기를 통한 건식혼합, 습식 Milling 혼합, 건식 Ball Mill 혼합 등을 실시하였다. Ball Mill 혼합의 경우가 가장 균일하게 혼합되었기 때문에, 값의 편차가 가장 적었고 열전도도 증가율이 가장 좋았다. 지금까지 수행된 시험에서 소량의 고열전도 물질의 첨가로 경주산 칼슘 벤토나이트의 열전도도를 1.0 W/mK 수준으로 용이하게 증가시킬 수 있음을 실험적으로 확인할 수 있었다. 결론적으로, 본 연구에서 제시된 열전도 향상 방법은, 첨가제 혼합이 벤토나이트의 기본 성질인 팽윤압과 수리전도도에 미치는 영향까지 제시된다면, 국내 고준위폐기물 처분장의 개념 설계에 유용하게 활용될 수 있을 것으로 기대된다.

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
    • /
    • 제25권
    • /
    • pp.55-59
    • /
    • 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.

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

  • 정민호;장기창;나호상;백영진;박성룡;유성연
    • 대한기계학회:학술대회논문집
    • /
    • 대한기계학회 2007년도 춘계학술대회B
    • /
    • pp.2102-2107
    • /
    • 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.

  • PDF

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

  • 장기창;정민호;윤형기;나호상;유성연
    • 한국신재생에너지학회:학술대회논문집
    • /
    • 한국신재생에너지학회 2007년도 춘계학술대회
    • /
    • pp.466-469
    • /
    • 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.

  • PDF