• Title/Summary/Keyword: Mass Transfer Resistance

검색결과 133건 처리시간 0.02초

External Condensation Heat Transfer Coefficients of Refrigerant Mixtures on a Smooth Tube

  • An, Kwang-Yong;Cho, Young-Mok;Seo, Kang-Tae;Jung, Dong-Soo
    • International Journal of Air-Conditioning and Refrigeration
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    • 제9권3호
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    • pp.1-9
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    • 2001
  • In this study, condensation heat transfer coefficients (HTCs) of nonazeotropic refrigerant mixtures of HFC32/HFC 134a and HCFC123 at various compositions were measured on a horizontal smooth tube. All data were taken at the vapor temperature of 39$^{\circ}C$ with a wall subcooling of 3~8K. Test results showed that HTCs of tested mixtures were 11.0~85.0% lowed than the ideal values calculated by the mass fraction weighting of the HTCs of the pure components. Thermal resistance due to the diffusion vapor film was partly responsible for the significant reduction of HTCs with these nonazeotropic mixtures. The measured data were compared against thc predicted ones by Colburn and Drew's film model and a good agreement was observed within a deviation of 15%.

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수평관에서 이원 혼합냉매의 응축 열전달계수 (Condensation Heat Transfer Coefficients of Binary Refrigerant Mixtures on a Horizontal Smooth Tube)

  • 김경기;서강태;정동수
    • 설비공학논문집
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    • 제12권12호
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    • pp.1049-1056
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    • 2000
  • In this study, condensation heat transfer coefficients(HTCs) of 2 nonazeotropic refrigerant mixtures of HFC32/HFC134a and HFC134a/HCFC123 at various compositions were measured on a horizontal smooth tube. All data were taken at the vapor temperature of 39$^{\circ}C$ with a wall subcooling of 3~8K. Test results showed that HTCs of tested mixtures were 11.0~85.0% lower than the ideal values calculated by the mass fraction weighting of the pure components HTCs. Thermal resistance due to the diffusion vapor film was partly responsible for the significant reduction of HTCs with these nonazeotropic mixtures. The measured data were compared against the predicted ones by Colburn and Drew\`s film model and a good agreement was observed.

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건조 조건하에서 TEDA주입 탄소층에 의한 Methyliodide 제거 효율에 관한 연구 (Study on the Removal Efficiency of a TEDA Impregnated Charcoal Bed for Methyliodide under Dry Condition)

  • Won Jim Cho;Soon Heung Chang
    • Nuclear Engineering and Technology
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    • 제16권2호
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    • pp.80-88
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    • 1984
  • Thriethylenediamine(TEDA)주입 활성탄층에 의한 공기중의 methyliodide 제거 메카니즘이 조사되었다. 실험 결과, 공기 유속이 20cm/sec 이상일 때는 기공확산이 율속 단계였으며, 10cm/sec 일때는 기공확산 저항과 외부 물질 전달 저항이 모두 총괄 물질 전달 저항에 기여하였다. 공기중 수증기가 존재하지 않는 건조 조건하에서의 TEDA 함침 탄소층의 성능을 묘사하기 위한 흡착 모델이 제안되었다. 계산된 값은 실험 결과와 잘 일치하였다.

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벼의 열전도계수와 열확산계수에 관한 기초연구 (Fundamental Studies on the Thermal conductivity and Thermal Diffusivity of Rough rice)

  • 김만수;고학균
    • Journal of Biosystems Engineering
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    • 제4권2호
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    • pp.53-63
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    • 1979
  • The knowlege of thermal properties of rough rice has become of greate importance to the analysis of heat and mass transfer phenomenon in rice drying and storage process. Some information is available on the thermal properties of rough rice in foreign countries but is not available for these properties in Korea. A fundamental study was made to determine the thermal conductivity and thermal diffusivity of rough rice with line source method and to select current and resistance suitable for these properties from investigating the effect of current and resistance of heating wire on the temperature rise. The result of this study may be summarized as follows ; 1. Even through the power per unit length of heating wires is about the same, the tendency of temperature rise showed a little difference among them , and the suitable range of it for thermal properties was found to be 3.56-5.37w/m. 2. the most desirable resistance and current of heating wire was 18.40 ohm/m, 0.44 amperes among three kinds of heating wires and currents, respectively. because it took 13 minutes or so for the heating wire to reach equilibrium temperature. 3. The thermal conductivity of rough rice was 0.120-0.130 w/m$ ^\circ C$. and thermal diffusivity of it was $5.8210 $\times10^{-8} -9.7529 $\times10^{-8} m^2 /s.$ 4.The thermal conductivity showed a little difference in variation with resistance of heating wire but the variation of current of heating wire at the same resistance did not affect the thermal conductivity , and the thermal diffusivity was not affected by the variation of resistance and current.

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열전달 촉진관에서 신냉매의 풀비등 열전달계수 (Pool Boiling Heat Transfer Coefficients of New Refrigerants on Various Enhanced Tubes)

  • 박진석;김종곤;정동수;김영일
    • 설비공학논문집
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    • 제13권8호
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    • pp.710-719
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    • 2001
  • Pool boiling heat transfer coefficients (HTCs) of HCFC123, HFC134a, HCFC22, HFC407C, HFC410A and HFC32 wre measured on a horizontal smooth tube, 26 fpi low fin tube, Turbo-B and Thermoexcel-E enhanced tubes. AN experimental apparatus was designed such that all tubes heated by cartridge heaters could be installed at the same time to save the refrigerant. Data were taken in the pool of $7^{\circ}C$ with the heat flux decreasing from 80 kW/$m^2\;to\;5kW/m^2$. Test results showed that HTCs of pure refrigerants and those of a azeotrope were greatly influenced by reduced pressure. HTCs of HFC407C were 21~25% lower than those of HCFC22 due to mass transfer resistance. For all refrigerants, enhanced tubes with sub-surface and sub-tunnels showed the largest heat transfer enhancement. Especially the largest heat enhancement was obtained for HCFC123 whose reduced pressure is the lowest among al the refrigerants tested. This indicates that either Turbo-B or Thermoexcel-E enhanced tube would be the best choice when used with a low vapor pressure refrigerant.

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평판 표면에서 HFC32/HFC152a 혼합냉매의 풀 비등 열전달계수 (Pool Boiling Heat Transfer Coefficient of HFC32/HFC152a on a Plain Surface)

  • 강동규;이요한;정동수
    • 설비공학논문집
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    • 제25권9호
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    • pp.484-492
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    • 2013
  • Nucleate pool boiling heat transfer coefficients (HTCs) are measured with HFC32/HFC152a mixture at several compositions. All data are taken at the liquid pool temperature of $7^{\circ}C$, on a horizontal plain square surface of $9.53{\times}9.53$ mm, with heat fluxes of 10 $kW/m^2$ to 100 $kW/m^2$ with an interval of 10 $kW/m^2$, in the increasing order of heat flux. Test results show that the HTCs of these mixtures are up to 45% lower than those of the ideal HTCs calculated by a linear mixing rule with pure fluids' HTCs, due to the mass transfer resistance associated with non-azeotropic refrigerant mixtures. Pool boiling data show the deduction in HTCs with an increase in GTD of the mixture. The present mixture data agree well with five well known correlations, within 20% deviation.

착상을 고려한 극저온 질소-대기 열교환기의 해석 (Analysis of a Cryogenic Nitrogen-Ambient Air Heat Exchanger Including Frost Formation)

  • 최권일;장호명
    • 설비공학논문집
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    • 제12권9호
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    • pp.825-834
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    • 2000
  • A heat exchanger analysis is performed to investigate the heating characteristics of cryogenic nitrogen by ambient air for the purpose of cryogenic automotive propulsion. The heat exchanger is a concentric triple-passage for supercritical nitrogen, and the radial fins are attached on the outermost tube for the crossflow of ambient air. The temperature distribution is calculated for the nitrogen along the passage, including the real gas properties of nitrogen, the fluid convections and the conductions through the tube walls and the fins. Since the wall temperature of the outer (ambient side) tube is very low in most cases, a heavy frost can be formed on the surface, affecting the heat exchange performance. By the method of the similarity between the heat and the mass transfer of moist air, the frost growth and the time-dependent effectiveness of the heat exchanger are calculated for various operating conditions. It is concluded that the frost formation can augment the heating of nitrogen during the initial period because of the latent heat, then gradually degrades the heat exchange because of the increased thermal resistance. Practical design issues are discussed for the flow rate of nitrogen, the velocity and humidity of ambient air, and the sizes of the fin.

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Effect of Anodic Gas Compositions on the Overpotential in a Molten Carbonate Fuel Cell

  • Lee C.G.;Kim D.H.;Hong S.W.;Park S.H.;Lim H.C.
    • 전기화학회지
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    • 제9권2호
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    • pp.77-83
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    • 2006
  • Anodic overpotential has been investigated with gas composition changes in a $100cm^2$ class molten carbonate fuel cell. The overpotential was measured with steady state polarization, reactant gas addition (RA), inert gas step addition (ISA), and electrochemical impedance spectroscopy (EIS) methods at different anodic inlet gas compositions, i.e., $H_2:CO_2:H_2O=0.69:0.17:0.14\;atm\;and\;H_2:CO_2:H_2O=0.33:0.33:0.33\;atm$, at a fixed $H_2$ flow rate. The results demonstrate that the anodic overpotential decreases with increasing $CO_2\;and\;H_2O$ flow rates, indicating the anode reaction is a gas-phase mass-transfer control process of the reactant species, $H_2,\;CO_2,\;and\;H_2O$. It was also found that the mass-transfer resistance due to the $H_2$ species slightly increases at higher $CO_2\;and\;H_2O$ flow rates. EIS showed reduction of the lower frequency semi-circle with increasing $H_2O\;and\;CO_2$ flow rate without affecting the high frequency semi-circle.

암모니아-물 랭킨사이클의 증발기에서의 엑서지 및 엔트랜시 성능 특성 해석 (Performance Characteristics Analysis of Evaporator in Ammonia-Water Rankine Cycle Based on Exergy and Entransy)

  • 김경훈;정영관
    • 한국수소및신에너지학회논문집
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    • 제30권6호
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    • pp.621-628
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    • 2019
  • The use of the ammonia-water zeotropic mixture as a working fluid in the power generating system has been considered as a proven technology for efficient recovery of low-grade heat sources. This paper presents a thermodynamic performance analysis for ammonia-water evaporator using low-grade heat source, based on the exergy and entransy which has been recently introduced as a physical quantity to describe the heat transfer ability of an object. In the analysis, effects of the ammonia mass fraction and source temperature of the binary mixture are investigated on the system performance such as heat transfer, effectiveness, exergy destruction, entransy dissipation, and entransy dissipation based thermal resistance. The results show that the ammonia mass concentration and the source temperature have significant effects on the thermodynamic system performance of the ammonia-water evaporator.

고분자 전해질 연료전지내의 양극 기체확산층 물성 변화가 전지성능에 미치는 영향에 관한 전산해석 연구 (Numerical Study on the Effect of Gas Diffusion Layer (GDL) Properties in Cathode on the Performance of Polymer Electrolyte Membrane Fuel Cell (PEMFC))

  • 전정환;조동현;이지영;김성현
    • Korean Chemical Engineering Research
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    • 제50권3호
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    • pp.556-561
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    • 2012
  • 본 연구에서는 고분자형 연료전지(PEMFC) 내의 기체확산층(GDL)에서의 물질 거동 전산해석을 통하여 GDL 물성이 전지성능에 미치는 영향을 알아보았다. GDL 내에서 기상의 산소와 액상의 물의 거동을 계산하기 위하여 multi-phase mixture($M^2$) 모델을 사용하였다. GDL의 접촉각, 기공도, 기체투과도, 두께에 변화를 주며 계산을 실시하여 GDL 내에서의 물질 거동의 변화를 확인 하였고, GDL 물성이 전지성능에 미치는 영향을 파악하였다. 전산해석 결과, GDL의 접촉각과 기공도가 커지고, 두께가 얇아짐에 따라 물질전달 저항이 감소하여 GDL과 촉매층 사이의 계면에서의 물포화도가 낮아지고 산소농도는 증가하여 전지성능이 향상되는 것을 확인하였다.