• Title/Summary/Keyword: Convective heat transfer coefficients

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Forced convective boiling heat transfer for a ternary refrigerant mixture inside a horizontal tube (수평관내 3성분 혼합냉매의 강제대류비등 열전달)

  • 오종택
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.11 no.6
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    • pp.912-920
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    • 1999
  • The forced convective boiling heat transfer coefficients of R-407C were measured inside a horizontal tube 6.0mm I.D. and 4.0m long. The heat transfer coefficients increased according to an increase in heat flux at constant mass flux. Because nucleation was completely suppressed in the two-phase flow region with high quality, heat transfer coefficients in forced convective evaporation were higher than those in nucleate boiling region. Average heat transfer coefficients of R-407C were about 30 percent lower than the pure refrigerant correlation, due to mass transfer resistance at the gas-liquid interface. However, the total experimental data shows an agreement with the predicted data for ternary refrigerant mixtures with a mean deviation of 30%.

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Heat Transfer Coefficients of Concentric Annuli for Testing Heat Transfer Characteristics of Alternative Refrigerants in Tubes (대체냉매 관내 열전달특성 시험을 위한 동심이중원관의 환상유로의 열전달계수)

  • KIM, MAN-HOE
    • Transactions of the Korean hydrogen and new energy society
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    • v.32 no.1
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    • pp.63-67
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    • 2021
  • Accurate measurements of the heat transfer coefficients of concentric annular space for the test section is important to measure the tube-side heat transfer coefficients of working fluids. This paper presents the annular side heat transfer coefficients of concentric annuli with variation of tube diameter ratios using Wilson plot method. The test facility has a straight, horizontal test section with an active length of 3.0 m. Inner/outer diameters of test tubes are 7.0/7.5 and 8.0/8.56 mm, respectively. An outer diameter of annulus side is 16.0 mm. The test results show that convective heat transfer coefficients in annuli increase with annular diameter ratio. The correlations for convective heat transfer coefficients in annuli are also developed.

Two phase convective heat transfer augmentation in swirl flow with non-boiling (비비등 선회유동에서의 2상 대류열전달 증가)

  • ;;Kim, J. G.
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.10
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    • pp.2586-2594
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    • 1995
  • Two phase flow phenomena are observed in many industrial facilities and make much importance of optimum design for nuclear power plant and various heat exchangers. This experimental study has been investigated the classification of the flow pattern, the local void distribution and convective heat transfer in swirl and non-swirl two phase flow under the isothermal and nonisothermal conditions. The convective heat transfer coefficients in the single phase water flow were measured and compared with the calculated results from the Sieder-Tate correlation. These coefficients were used for comparisons with the two-phase heat transfer coefficients in the flow orientations. The experimental results indicate, that the void probe signal and probability density function of void distribution can used into classify the flow patterns, no significant difference in voidage distribution was observed between isothermal and non-isothermal condition in non-swirl flow, the values of two phase heat transfer coefficients increase when superficial air velocities increase, and the enhancement of the values is observed to be most pronounced at the highest superficial water velocity in non-swirl flow. Also two phase heat transfer coefficients in swirl flow are increased when the twist ratios are decreased.

A Study on the Effect of Fin Pitch of Offsets Strip Fin on Heat Transfer of High Prandtl Fluid (옵셋 스트립 휜의 휜피치가 고 Prandtl 유체 열전달 특성에 미치는 영향)

  • 강덕종;양대일;전승환;정형호
    • Journal of Advanced Marine Engineering and Technology
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    • v.26 no.1
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    • pp.83-89
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    • 2002
  • In the present study, heat transfer characteristics of oil flow over offset strip fins were predicted by the numerical methods. Oil flow in the plate-fin passage was idealized by 2 dimensions. The flow patterns and heat transfer characteristics were predicted in details. Numerical results shows that the average convective heat transfer coefficients are almost independent on the raws of fins and affected by fin pitches. At the rear face of fin, there exists minimum point of heat transfer coefficients where stream are separated from the fin surfaces. The convective heat transfer coefficients were effected by separation bubbies which appeared at the wake region of offset strip fins.

Measuring Convective Heat Transfer Coefficient of Nanofluids Considering Effect of Film Temperature Change over Heated Fine Wire (막온도 변화를 고려한 가는 열선주위 나노유체의 대류열전달계수 측정 실험)

  • Lee, Shinpyo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.37 no.8
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    • pp.725-732
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    • 2013
  • This study examined the convective heat transfer characteristics of nanofluids flowing over a heated fine wire. Convective heat transfer coefficients were measured for four different nano-engine-oil samples under three different temperature boundary conditions, i.e., both or either variation of wire and fluid temperature and constant film temperature. Experimental investigations that the increase in the convective heat transfer coefficients of nanofluids in the internal pipe flow often exceeded the increase in thermal conductivity were recently published; however, the current study did not confirm these results. Analyzing the behavior of the convective heat transfer coefficient under various temperature conditions was a useful tool to explain the relation between the thermal conductivity and the boundary layer thickness of nanofluids.

Prediction of Forced Convective Boiling Heat Transfer Coefficient of Pure Refrigerants and Binary Refrigerant Mixtures Inside a Horizontal Tube

  • Kim, Min-Soo;Hong, Eul-Cheong;Shin, Jee-Young;Kyungdoug Min;Ro, Sung-Tack
    • Journal of Mechanical Science and Technology
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    • v.17 no.6
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    • pp.935-944
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    • 2003
  • Forced convective boiling heat transfer coefficients were predicted for an annular flow inside a horizontal tube for pure refrigerants and nonazeotropic binary refrigerant mixtures. The heat transfer coefficients were calculated based on the turbulent temperature profile in liquid film and vapor core considering the composition difference in vapor and liquid phases, and the nonlinearity in mixing rules for the calculation of mixture properties. The heat transfer coefficients of pure refrigerants were estimated within a standard deviation of 14% compared with available experimental data. For nonazeotropic binary refrigerant mixtures, prediction of the heat transfer coefficients was made with a standard deviation of 18%. The heat transfer coefficients of refrigerant mixtures were lower than linearly interpolated values calculated from the heat transfer coefficients of pure refrigerants. This degradation was represented by several factors such as the difference between the liquid and the overall compositions, the conductivity ratio and the viscosity ratio of both components in refrigerant mixtures. The temperature change due to the concentration gradient was a major factor for the heat transfer degradation and the mass flux itself at the interface had a minor effect.

Correlation of Convective Boiling Heat Transfer in a Horizontal Tube for Pure Refrigerants and Refrigerant Mixtures (순수 및 혼합냉매의 유동증발 열전달 상관식)

  • Shin, J.Y.;Kim, M.S.;Ro, S.T.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.8 no.2
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    • pp.254-266
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    • 1996
  • Boiling heat transfer coefficients of pure refrigerants(R22, R32, R125, R134a, R290, and R600a) and refrigerant mixtures(R32/R134a and R290/R600a) are measured experimentally and compared with several correlations. Convective boiling term of Chen's correlation predicts experimental data for pure refrigerants fairly well(root-mean-square error of 12.1% for the quality range over 0.2). An analysis of convective boiling heat transfer of refrigerant mixtures is performed for an annular flow to study degradation of heat transfer. Annular flow is the subject of this analysis because a great portion of the evaporator in refrigeration or air conditioning system is known to be in the annular flow regime. Mass transfer effect due to composition difference between liquid and vapor phases, which is considered as a driving force for mass transfer at interface, is included in this analysis. Correction factor $C_F$ is introduced to the correlation for the pure substances through annular flow analysis to apply the correlation to the mixtures. The flow boiling heat transfer coefficients are calculated using the correlation considering nucleate boilling effect in the low quality region and mass transfer effect for nonzazeotropic refrigerant mixtures.

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Comparative Investigation of Convective Heat Transfer Coefficients for Analyzing Compressed Hydrogen Fueling Process (압축 수소 충전 공정 해석을 위한 대류 열전달 계수 비교 분석)

  • Hyo Min Seo;Byung Heung Park
    • Journal of the Korean Institute of Gas
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    • v.27 no.3
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    • pp.123-133
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    • 2023
  • Commercial hydrogen fuel cell vehicles are charged by compressing gaseous hydrogen to high pressure and storing it in a storage tank in the vehicle. This process causes the temperature of the gas to rise, to ensure the safety to storage tanks, the temperature is limited. Therefore, a heat transfer model is needed to explain this temperature rise. The heat transfer model includes the convective heat transfer phenomenon, and accurate estimation is required. In this study, the convective heat transfer coefficient in the hydrogen fueling process was calculated and compared using various correlation equations considering physical phenomena. The hydrogen fueling process was classified into the fueling line from the dispenser to the tank inlet and the storage tank in the vehicle, and the convective heat transfer coefficients were estimated according to process parameters such as mass flow rate, diameter, temperature and pressure. As a result, in the case of the inside of the filling line, the convective heat transfer coefficient was about 1000 times larger than that of the inside of the storage tank, and in the case of the outside of the filling line, the convective heat transfer coefficient was about 3 times larger than that of the outside of the storage tank. Finally, as a result of a comprehensive analysis of convective heat transfer coefficients in each process, it was found that outside the storage tank was lowest in the entire hydrogen fueling process, thus dominated the heat transfer phenomenon.

A Study on the Heat Transfer Characteristics of Oil Flow over Offset Strip Fins (옵셋 스트립 휜에서 오일유동의 열전달 특성에 관한 연구)

  • 양대일;정형호
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.11
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    • pp.1134-1140
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    • 2001
  • In the present study, heat transfer characteristics of oil flow over offset strip fins were predicted by the numerical methods. Oil flow in the plate-fin passage was idealized by 2 dimension. Power law scheme and SIMPLE algorithm were used for convective diffusion formulation and pressure term respectively. Governing equations were discretized by control volume formulation. The flow patterns and heat transfer were predicted in details. The convective heat transfer coefficients were affected by separation bubbles which appeared at the wake region of offset strip fins.

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Effects of the Inlet Boundary Layer Thickness and the Boundary Layer Fence on the Heat Transfer Chracteristics in a Turbine Cascade (입구경계층 두께와 경계층 펜스가 터빈 캐스케이드내 열전달 특서에 미치는 영향)

  • Jeong, J.S.;Chung, J.T.
    • Proceedings of the KSME Conference
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    • 2001.06d
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    • pp.765-770
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    • 2001
  • The objective of the present study is to investigate the effects of the various inlet boundary layer thickness on convective heat transfer distribution in a turbine cascade endwall and blade suction surface. In addition, the proper height of the boundary layer fences for various inlet boundary layer thickness were applied to turbine cascade endwall in order to reduce the secondary flow, and to verify its influence on the heat transfer process within the turbine cascade. Convective heat transfer distributions on the experimental regions were measured by the image processing system. The results show that heat transfer coefficients on the blade suction surface were increased with an augmentation of inlet boundary layer thickness. However, in a turbine cascade endwall, magnitude of heat transfer coefficients did not change with variation of inlet boundary layer thickness. The results also present that the boundary layer fence is effective in reducing heat transfer on the suction surface. On the other hand, in the endwall region, boundary layer fence brought about the subsidiary heat transfer increment.

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