• Title, Summary, Keyword: Characteristics of Heat Transfer

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A Study on the Heat Transfer Characteristics of a Self-Oscillating Heat Pipe

  • Yoon, Seok-Hun;Cheol Oh;Park, Jae-Hyuk
    • Journal of Mechanical Science and Technology
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    • v.16 no.3
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    • pp.354-362
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    • 2002
  • In this paper, the heat transfer characteristics of a self-oscillating heat pipe are experimentally investigated for the effect of various working fluid fill charge ratios and heat loads. The characteristics of temperature oscillations of the working fluid are also analysed based on chaotic dynamics. The heat pipe is composed of a heating section, a cooling section and an adiabatic section, and has a 0.002m internal diameter, a 0.34m length in each turn and consists of 19 turns. The heating and the cooling portion of each turn has a length of 70mm. A series of experiments was carried out to measure the temperature distributions and the pressure variations of the heat pipe. Furthermore, heat transfer performance, effective thermal conductivity, boiling heat transfer and condensation heat transfer coefficients are calculated for various operating conditions. Experimental results show the efficacy of this type of heat pipe.

Experimental study on the characteristics of heat transfer for new type aluminum tube (신형 알루미늄관의 열전달 특성에 관한 실험적 연구)

  • 문춘근;윤정인;김재돌
    • Journal of the Korean Society of Marine Engineering
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    • v.24 no.2
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    • pp.31-37
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    • 2000
  • This study investigated heat transfer characteristics of refrigeration system using new type aluminium heat transfer tube for evaporator of refrigeration and air-conditioning comparing with bare tube. From the result of heat transfer experiment form one phase flow using cooled and hot water, about 20% heat transfer performance is superior in case of same quantity of flow and about 4% heat transfer performance if superior in case of same velocity comparing with bare tube. Casing of two phase flow, heat transfer performance of new type aluminum heat transfer tube shows about 50% superior heat transfer performance comparing with bare tube in the same evaporating pressure when using heat transfer tube as evaporator and shows about 47% increase when expressing performance coefficient as the rate of refrigerating capacity and compressing work. However, it can be known that pressure drop in the heat transfer tube is taken higher value of about 18% in case of new type aluminum heat transfer tube. From the above result, new type aluminum heat transfer tube is excellent comparing with bare heat transfer tube using the existing heat exchanger for refrigerator.

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An Experimental Study on the Heat Transfer Characteristics of Corrugated Impinging Jets (파형 충돌분류의 열전달 특성에 관한 실험적 연구)

  • Kim, Ye Yong;Kim, Kui Soon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.3
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    • pp.320-329
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    • 1999
  • An experimental study has been performed to investigate the heat transfer characteristics of impinging jets with corrugated nozzle and wake generation plate. Three different shapes of corrugated nozzle and five different shapes of wake generation plate were tested to improve the heat transfer characteristics of impinging jet. Heat transfer coefficients were obtained by using transient method based on the liquid crystal thermography. The effects of corrugated nozzle and wake generation plate on the heat transfer characteristics of impinging jets were discussed in detail. The results showed that both the corrugated nozzle and the wake generation plate improved the heat transfer characteristics of impinging jet. Especially, heat transfer coefficients around stagnation region of impinging jets were highly increased.

Conjugate Heat Transfer Characteristics in a Ribbed Channel:Effect of Reynolds Number and Heat Capacity Ratio (요철이 설치된 채널 내에서 레이놀즈수와 열용량비에 따른 복합열전달 특성)

  • Song, Jeong-Chul;Ahn, Joon;Lee, Joon-Sik
    • Proceedings of the KSME Conference
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    • pp.2297-2302
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    • 2007
  • Numerical simulations are conducted to analyze conjugate heat transfer characteristics in a ribbed channel. In this simulation, the effects of Reynolds number and heat capacity of the solid channel wall on convective heat transfer are observed in the turbulent flow regime. In the case of the conducting wall against isothermal wall, the relative ratio of the thermal resistance between the solid wall and the flow field varies with Reynolds number. Thus the characteristics of the conjugate heat transfer are changed with the Reynolds number. Heat capacity ratio affects the temperature fluctuation inside solid wall. The temperature fluctuation inside the solid wall decreases with increasing the heat capacity of the solid wall so that the convective heat transfer increases. When the thermal conductivity ratio is smaller than 10, the effects of flow characteristics on heat transfer are changed.

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EXPERIMENTAL INVESTIGATION OF CONVECTIVE HEAT TRANSFER IN A NARROW RECTANGULAR CHANNEL FOR UPWARD AND DOWNWARD FLOWS

  • Jo, Daeseong;Al-Yahia, Omar S.;Altamimi, Raga'i M.;Park, Jonghark;Chae, Heetaek
    • Nuclear Engineering and Technology
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    • v.46 no.2
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    • pp.195-206
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    • 2014
  • Heat transfer characteristics in a narrow rectangular channel are experimentally investigated for upward and downward flows. The experimental data obtained are compared with existing data and predictions by many correlations. Based on the observations, there are differences from others: (1) there are no different heat transfer characteristics between upward and downward flows, (2) most of the existing correlations under-estimate heat transfer characteristics, and (3) existing correlations do not predict the high heat transfer in the entrance region for a wide range of Re. In addition, there are a few heat transfer correlations applicable to narrow rectangular channels. Therefore, a new set of correlations is proposed with and without consideration of the entrance region. Without consideration of the entrance region, heat transfer characteristics are expressed as a function of Re and Pr for turbulent flows, and as a function of Gz for laminar flows. The correlation proposed for turbulent and laminar flows has errors of ${\pm}18.25$ and ${\pm}13.62%$, respectively. With consideration of the entrance region, the heat transfer characteristics are expressed as a function of Re, Pr, and $z^*$ for both laminar and turbulent flows. The correlation for turbulent and laminar flows has errors of ${\pm}19.5$ and ${\pm}22.0%$, respectively.

An experimental study on the heat transfer augmentation by using the multiple orifice nozzle (다중 오리피스 노즐을 이용한 충돌분류의 열전달 향상에 관한 실험적 연구)

  • 김예용;정기호;김귀순;서태범
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.11 no.5
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    • pp.647-657
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    • 1999
  • An experimental study has been peformed to investigate the heat transfer characteristics of impinging jets with multiple orifice nozzles. Four different shapes of multiple orifice nozzle were tested to improve the heat transfer characteristics of impinging jet. Heat transfer coefficients were obtained by using transient and steady method based on the liquid crystal thermography, and both methods showed very similar results. The effects of multiple orifice nozzles on the heat transfer characteristics of impinging jets were discussed in detail. The results showed that multiple orifice nozzles improved the heat transfer characteristics of impinging jet. Especially, heat transfer coefficients around stagnation region of impinging jets were highly increased.

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Heat Transfer Characteristics on Design Conditions of Finned-Tube Evaporators (설계조건에 따른 핀-튜브 증발기의 열전달 특성)

  • 강희정;이윤수;권영철;장근선;김영재
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.1
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    • pp.46-54
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    • 2002
  • To investigate the design effects of a heat exchanger on a tube type, a tube circuit and a fin pitch, an experimental study on the heat transfer characteristics of finned- tube evaporators was performed. The refrigerant was R-22. A refrigerant loop was established to measure the heat transfer rate, the air heat transfer coefficient. The experimental results showed that the heat transfer characteristics of the evaporators were affected by the design parameters. And the heat transfer rate of the slit fin was better about 25%, compared to those of the louver fin. In the present experimental range, the heat transfer performance with the straight tube circuit was more remarkable than that of the zigzag tube circuit, as seen from temperature variations of the evaporator exit. $\jmath$-factor on the tube type, the tube circuit and the fin pinch decreased, as increasing Reynolds number.

A Study on the Heat Transfer Characteristics of Loop Type Capillary Heat Pipe (루프형 세관 히트 파이프의 열전달특성에 관한 연구)

  • Yoon, Suck-Hun;Choi, Jae-Hyuck
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.3
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    • pp.346-353
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    • 2000
  • In this paper, heat transfer characteristics of a loop type capillary heat pipe were experimentally investigated for the effect of several fill charge ratios of working fluid and heat loads. This type of heat pipe consists of a heating section, a cooling section and an adiabatic section. The heat pipe used has a 0.002m internal diameter, a 0.34m length in one turn and consists of 19 turns. Heating and cooling sections each have a length of 70mm. Experiments were performed to measure the temperature distributions and the pressure variation of the heat pipe. Heat transfer performance, effective thermal conductivity, boiling heat transfer and condensation heat transfer coefficients were calculated for various operating conditions of heat pipe and it was found that heat transfer characteristics of this type heat pipe were very excellent. As shown by this experimental study, this type of heat pipe operates by oscillatory flow caused by pressure and temperature oscillations.

Heat/Mass Transfer Characteristics on Shroud with Turbine Blade Tip Clearances (터빈 블레이드 말단과 슈라우드 사이의 간극변화에 따른 슈라우드에서의 열/물질전달 특성)

  • Lee, Dong-Ho;Choe, Jong-Hyeon;Jo, Hyeong-Hui
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.3
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    • pp.414-421
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    • 2001
  • The present study is conducted to investigate the local heat/mass transfer characteristics on the shroud with blade tip clearances. The relative motion between blade and shroud has little influence on the overall heat transfer characteristics, except some local effects. Therefore, the relative motion between the blade and shroud is neglected in this study. A naphthalene sublimation method is employed to determine the detailed local heat/mass transfer coefficients on the surface of the shroud. The tip clearance is changed from 0.66% to 2.85% of the blade chord length. The flow enters the gap between the blade tip and shroud at the pressure side due to the pressure difference. Therefore, the heat/mass transfer characteristics on the shroud are changed significantly from those with endwall. At first, high heat/mass transfer occurs along the profile of blade at the pressure side due to the entrance effect and acceleration of the gap flow. Then, the heat/mass transfer coefficients on the shroud increase along the suction side of the blade because tip leakage vortices are generated and interact with the main flow. The results show that the heat/mass transfer characteristics are changed largely with the gap distance between the tip of turbine blade and the shroud.

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.