• Title, Summary, Keyword: Heat Transfer Coefficient

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A Experimental Study on the Boiling Heat Transfer Characteristics of Nanofluids by the Size and Mixing Ratio of Graphene Particle (그래핀 입자의 크기와 혼합비율이 나노유체의 비등열전달에 미치는 영향에 대한 실험적 연구)

  • Park, Sung-Seek;Kim, Young Hun;Kim, Nam-Jin
    • Journal of the Korean Solar Energy Society
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    • v.35 no.2
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    • pp.53-62
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    • 2015
  • Boiling heat transfer characteristic is very important in the various industries such as solar thermal system, power generation, heat exchangers, cooling of high-power electronics components and cooling of nuclear reactors. Therefore, in this study, boiling heat transfer characteristics such as critical heat flux (CHF) and heat transfer coefficient under the pool boiling state were tested using graphene nanofluids. Graphene used in this study, which have the same thermal conductivity but with different sizes. The experimental results showed that the highest the CHF and boiling heat transfer coefficient increase ratio for graphene nanofluids was at the 0.01 vol.%. At the present juncture, the CHF and boiling heat transfer coefficient increase ratio of the small-sized graphene nanofluids was higher than the large-sized graphene nanofluids.

Heat Transfer Coefficients of Individual Rows for Fin-and-Tube Heat Exchangers (휜-관 열교환기의 열별 열전달 계수 측정)

  • Shin, T.R.;Lee, E.R.;Kim, N.H.
    • Proceedings of the KSME Conference
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    • pp.1034-1039
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    • 2004
  • The row-by-row heat transfer characteristics of fin-and-tube heat exchangers having wavy fins were experimentally investigated. Three samples having different rows (one, two and three) were tested. Results show that the heat transfer coefficient is strongly dependent on the tube row. The heat transfer coefficient of the first row is larger than those of second or third rows. However, the difference decreases as the Reynolds number increases. The heat transfer coefficients of the second and the third row are approximately the same, probably due to increased mixing of bulk flow by wavy channels. Although samples have different tube row, the heat transfer coefficients of same row are approximately the same.

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Measurement of The Thermal Transfer Coefficient Predicting Efficiency of The Heat Pipe (히트파이프 성능예측 열전달계수 측정)

  • Lim, Soo-Jung;Moon, Jong-Min;Rhee, Gwang-Hoon
    • Proceedings of the KSME Conference
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    • pp.2039-2042
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    • 2008
  • Recently, Electronic & Electrical Products have problems how to reduce heat in trend reducing size and increasing speed. heat pipes worked by latent heats can solve problems for effective and quiet electronic applications. Heat Pipes have to be suitably designed for the external conditions due to showing optimum performance. it has influence on efficiency of heat pipes to the exterior structure changed by length, bending angle, diameter. Designing heat pipes has depended on experience from trial and error. this method wasted too many resources, but can't guarantee efficiency. to prevent those wastes, this study aims at making the thermal transfer coefficient predicting efficiency. In this study, the thermal transfer coefficient has been made from experimental results that used variables - lengths between heat source and radiation, bending angles, diameters of heat pipes. variables become non-dimensional in modeling process for making the coefficient.

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Flow Boiling Heat Transfer of R-410A in 0.5mm & 3.0mm Diameter Horizontal Tube (R-410A 비등열전달에 미치는 미세관경 0.5mm와 3.0mm의 영향)

  • Pamitran, A.S.;Choi, Kwang-Il;Oh, Jong-Taek;Hrnjak, Pega
    • Proceedings of the SAREK Conference
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    • pp.154-159
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    • 2008
  • Two-phase flow boiling heat transfer of R-410A in horizontal small tubes was reported in the present experimental study. The local heat transfer coefficients were obtained over a heat flux range of 5 to 40 kW/$m^2$, a mass flux range of 170 to 600 kg/$m^2s$, a saturation temperature range of 3 to $10^{\circ}C$, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 0.5 and 3.0 mm, and lengths of 330 and 3000 mm, respectively. The section was heated uniformly by applying a direct electric current to the tubes. The effects on heat transfer of mass flux, heat flux, inner tube diameter, and saturation temperature were presented. The experimental heat transfer coefficient is compared with six existing heat transfer coefficient correlations. A new boiling heat transfer coefficient correlation based on the superposition model for R-410A in small tubes was developed with mean deviation of 10.13%.

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A Study on Improvement of Engine Cooling System (엔진 냉각 시스템 개선에 관한 연구)

  • Kim, M.H.;Oh, B.W.
    • Transactions of the Korean Society of Automotive Engineers
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    • v.2 no.2
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    • pp.103-116
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    • 1994
  • In this study the behavior of engine cooling loss and overall heat transfer coefficient were studied experimentally using naturally aspirated engine and turbo charged engine. Using turbo charging, heat dissipation was increased because of the density of the mixture was increased with increment of inlet air flow rate. Therefore, cooling loss of turbo charged engine is larger than naturally aspirated engine. As taking the measurement of surface temperature of combustion chamber, gas heat transfer coefficient was calculated and found that it has greatly affected to overall heat transfer coefficient. The empirical formula of overall heat transfer coefficient established in order to predict of engine cooling loss and express only as a function of mean piston velocity.

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Heat Transfer Characteristics of Individual Rows for Fin-and-Tube Heat Exchangers (핀-관 열교환기의 열별 열전달 특성)

  • Kim, Nae-Hyun;Shin, Tae-Ryong;Han, Sung-Pil
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.19 no.2
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    • pp.149-155
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    • 2007
  • The row-by-row heat transfer characteristics of fin-and-tube heat exchangers were experimentally investigated. Three wavy fin samples having different rows (one, two and three) and one plain fin sample (three row) were tested for $600{\leq}Re_{D}{\leq}4,000$. The heat transfer data were obtained for individual rows, and the corresponding heat transfer coefficients were reduced from the data. Results showed that the heat transfer coefficients were strongly dependent on the tube row. The heat transfer coefficient decreased as the tube row increased. However, the row effect was different depending on the fin shape. For the wavy fin, the row effect significantly decreased as the Reynolds number increased, yielding approximately the same heat transfer coefficients at $Re_{D}{\approx}2,500$. For the plain fin, however, the row effect lasted for the whole Reynolds number range. The increased mixing of bulk flow by wavy channels appears to induce high heat transfer coefficient (accordingly diminishing row effect) at downstream rows. The heat transfer coefficients of individual rows were higher for heat exchangers having larger tube rows.

Analysis of Heat Transfer Characteristics in Response to Water Flow Rate and Temperature in Greenhouses with Water Curtain System (수막하우스의 유량 및 수온에 따른 열전달 특성 분석)

  • Kim, Hyung-Kweon;Kim, Seoung-Hee;Kwon, Jin-Kyeong
    • Protected Horticulture and Plant Factory
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    • v.25 no.4
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    • pp.270-276
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    • 2016
  • This study analysed overall heat transfer coefficient, heat transmission, and rate of indoor air heating provided by water curtain in order to determine the heat transfer characteristic of double-layered greenhouse equipped with a water curtain system. The air temperatures between the inner and outer layers were determined by the water flow rate and inlet water temperature. Higher water flow rate and inlet water temperature resulted in the increased overall heat transfer coefficient between indoor greenhouse air and water curtain. However, it was found that with higher levels of water flow rate and inlet water temperature, indoor overall heat transfer coefficient was converged about $10W{\cdot}m^{-2}{\cdot}^oC^{-1}$. The low correlation of overall heat transfer coefficient between water curtain and air within double layers was likely because the combination of greenhouse shape, wind speed and outdoor air temperature as well as water curtain affected the heat transfer characteristics. As water flow rate and inlet water temperature increased, the heat transferred into the greenhouse by water curtain also tend to rise. However it was demonstrated that the rate of heat transmission from water curtain into greenhouse with water curtain system using underground water was accounted for 22% to 28% for total heat lost by water curtain. The results of this study which quantify heat transfer coefficient and net heat transfer from water curtain may be a good reference for economical design of water curtain system.

Experimental Investigation of the Thermal Hydraulics in Lead Bismuth Eutectic-Helium Experimental Loop of an Accelerator-Driven System

  • Xi, Wenxuan;Wang, Yongwei;Li, Xunfeng;Huai, Xiulan;Cai, Jun
    • Nuclear Engineering and Technology
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    • v.48 no.5
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    • pp.1154-1161
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    • 2016
  • The heat transfer characteristics between liquid lead bismuth eutectic (LBE) and helium are of great significance for the two-loop cooling system based on an accelerator-driven system (ADS). This paper presents an experimental study on the resistance characteristics and heat transfer performance in a LBE-helium experimental loop of ADS. Pressure drops in the LBE loop, the main heat transfer, and the coupled heat transfer characteristics between LBE and helium are investigated experimentally. The temperature of LBE has a significant effect on the LBE thermo-physical properties, and is therefore considered in the prediction of pressure drops. The results show that the overall heat transfer coefficient increases with the increasing helium flow rate and the decreasing inlet temperature of helium. Increasing the LBE Reynolds number and LBE inlet temperature promotes the heat transfer performance of main heat transfer and thus the overall heat transfer coefficient. The experimental results give an insight into the flow and heat transfer properties in a LBE-helium heat exchanger and are helpful for the optimization of an ADS system design.

Heat Transfer Analysis of Coupled Electromagnetic-Thermal Field for Power Transformer (전자계-열계 결합해석에 의한 전력용 변압기의 열전달 해석)

  • Ahn, Hyun-Mo;Oh, Yeon-Ho;Hahn, Sung-Chin
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.58 no.11
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    • pp.2155-2161
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    • 2009
  • In this paper, we dealt with the electro-thermal coupling analysis for temperature prediction of power transformer. Heat transfer coefficient are calculated using Nusselt number in accordance with heat source generated from transformer windings and core materials. The calculated temperatures in power transformer were compared to those of measured ones and showed good agreement. This coupling method using heat transfer coefficient can be used at the design stage of power transformer efficiently.

Heat Transfer Characteristics of a Horizontal Fin Tube in a Fluidized Bed Combustor (유동층 연소로 내에서 수평전열관의 열전달 특성에 관한 연구)

  • 맹민재;정준기;정태용
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.9
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    • pp.2365-2372
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    • 1995
  • The objective of this study is to get the basic data for the development of fluidized bed combustor. For this purpose, various rake angles(.theta.=20.deg., 25.deg., 30.deg., 35.deg.) of finned tubes and a smooth tube were installed horizontally in the fluidized bed combustor of 410*250mm. The effect of fluidized bed temperature, superficial velocity in bed, size of bed materials, rake angle of finned tubes on the heat transfer coefficient was experimentally investigated. The following results were obtained. (1) Under the fluidized bed temperature(750.deg. C-900.deg. C), and the gas velocity in bed(1.1-2.8m/sec), The highest heat transfer coefficient was measured with the rake angle of finned tubes was .theta.=25.deg. and .theta.=35.deg. for the average fluidized material particle size of 1.22mm and 1.54mm, respectively. Generally, the heat transfer coefficient of finned tubes is 1.4 to 2.4 times larger than that of smooth tubes. (2) The size of bed materials influences the rake angle of finned tubes which can have the highest heat transfer coefficient. As the temperature in bed gets higher, the effect of the rake angle of finned tubes on the heat transfer coefficient becomes greater.