• Title/Summary/Keyword: Nusselt수

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A Study on the Heat Transfer Characteristics of Surface Radiation-Natural Convection Interactions in an Enclosure for Various Adiabatic Wall Thicknesses (단열벽체두께가 변화되는 밀폐공간에서 복사-자연대류열전달특성에 관한 연구)

  • Kwon, Y.I.;Yoo, J.O.;Kwon, S.S.
    • Solar Energy
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    • v.15 no.3
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    • pp.39-52
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    • 1995
  • This study is investigated numerically on the heat transfer characteristics of surface radiation-natural convection interactions in a two dimensional enclosure assumed Ondol cavity. Mean Nusselt number of the bottom surface with surface radiation is increased by increasing wall emissivity and by decreasing dimensionless thickness of adiabatic wall. and is greater than that without radiation. Mean Nusselt number of the bottom surface for convection only with surface radiation is slightly smaller than that without surface radiation with decrease dimensionless thickness of adiabatic wall.

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내부열원을 갖는 Top-vented 원통형 밀폐공간에서의 자연대류 연구

  • Kang, Kwon-Ho;Shin, Hyun-Gyu;Shin, Chi-Beom;Yoo, Jae-Seok;Kim, Chul;Park, Young-Mu
    • Proceedings of the Korea Society for Energy Engineering kosee Conference
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    • 1996.10b
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    • pp.176-180
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    • 1996
  • 본 연구에서는 감손우라늄 폐기물칩의 처리 장치인 공기조절식 산화장치의 열전달 특성을 실험적으로 해석하였다. 감손우라늄칩의 산화처리시 발생되는 산화열에 의한 장치 내부의 온도상승 및 외부로의 열전달을 해석하기 위해 산화장치 내부에 히터를 설치하여 실험을 수행하였으며, 히터의 발생열량을 시간에 따른 열전달 특성을 알아보기 위하여 Nusselt수, Grahsof수와 Rayleigh수를 구하고, Nusselt수와 Rayleigh수의 관계를 구하였다.

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Pressure Loss and Forced Convective Heat Transfer in an Annulus Filled with Aluminum Foam (발포 알루미늄이 삽입된 환형관에서의 압력손실 및 강제대류 열전달)

  • Noh Joo-Suk;Lee Kye-Bock;Lee Chung-Gu
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.17 no.9
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    • pp.855-862
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    • 2005
  • An experimental investigation has been carried out for aluminum foam heat sink inserted into the annulus to examine the feasibility as a heat sink for high performance forced water cooling in the annulus. The local wall temperature distribution, inlet and outlet pressures and temperatures, and heat transfer coefficients were measured for heat flux of 13.6, 18.9, 25.1, 31.4 $kw/m^2$ and Reynolds number ranged from 120 to 2000. Experimental results show that the friction factor is higher than clear annulus without aluminum foam, while the significant augmentation in Nu is obtained. This technique can be used for the compactness of the heat exchanger.

Natural Free Convection of Air in a Vertical Open Tube With Uniform Heat Flux and Temperature (일정 열류속 및 온도조건하의 수직관내에서 공기의 자연대류 열전달 연구)

  • Son, Byung-Jin;Kang, Hee-Yung
    • The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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    • v.12 no.4
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    • pp.234-239
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    • 1983
  • The natural free convection in a vertical tube with uniform heat flux and temperature has been studied by the theoretical analysis is of governing equations and experimental measurements. In order to determine the Characteristics of Convective heat transfer in the tube, a dimensionless Rayleigh number is introduced. The relationship between Nusselt and Rayleigh number is compared with the numerical analysis of finite difference method and experiment. Nusselt number obtained from the experimental measurements are in a good agreement with the calculated values, and the relationship equations between Nusselt and Rayleigh number are obtained.

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Heat Transfer by an Oscillating Flow in a Circular Pipe with Sinusoidal Wall Temperature Distributions (벽온도분포가 정현파인 원관에서 왕복유동에 의한 열전달 해석)

  • 이대영;박상진;노승탁
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.12
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    • pp.3208-3216
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    • 1993
  • Heat transfer characteristics of the laminar oscillating flow in a circular pipe have been studied under the condition that the wall temperature of the pipe is distributed sinusoidally with the axial direction. The axial velocity was assumed to be uniform in radial direction and the temperature field was analyzed by means of the perturbation method. The results show that the difference between wall and section-time-averaged fluid temperature increases as the oscillating frequency increases and eventually converges to a constant value which is determined by the ratio of swept distance to the characteristic length of wall temperature distribution. Also it is shown that the dominant variable in the heat transfer process when swept distance ratio is greater than 1 is not thermal Womersley number(F) but thermal Womersley number multiplied by the square root of swept distance ratio. The variation of the time-averaged Nusselt number is obtained as a function of F. The results indicate that Nusselt number is proportional to $F_{\epsilon}^{1/2}$ when both of F and .epsilon. are much greater than 1.

An Analysis of Unsteady 2-D Heat Transfer of the Thermal Stratification Flow inside Horizontal Pipe with Electrical Heat Tracing (Heat Tracing이 있는 수평배관 내부 열성층 유동의 비정상 2차원 열전달 해석)

  • 정일석;송우영
    • Journal of Energy Engineering
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    • v.6 no.2
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    • pp.119-128
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    • 1997
  • A method to mitigate the thermal stratification flow of a horizontal pipe line is proposed by heating external bottom of the pipe with electrical heat tracing. Unsteady two dimensional model has been used to numerically investigate an effect of the external heating on the thermal stratification flow. The dimensionless governing equations are solved by using the control volume formulation and SIMPLE algorithm. Temperature distribution, streamline profile and Nusselt number distributions are analyzed under heating conditions. The numerical results of this study show that the maximum dimensionless temperature difference between hot and cold sections of the inner wall of pipe is 0.424 at dimensionless time of 1,500 and the thermal stratification phenomenon disappears at about dimensionless time of 9,000.

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Cooling of a Rotating Heated Flat Plate by Water Jet Impingement (회전전열평판(回轉傳熱平板)의 충돌수분류(衝突水噴流)에 의한 냉각(冷却))

  • Jeon, Sung-Taek;Kim, Yeun-Young;Lee, Jong-Su;Park, Jong-Suen;Lee, Doug-Bong
    • Solar Energy
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    • v.15 no.2
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    • pp.47-64
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    • 1995
  • An experimental investigation is carried out to see the local heat transfer characteristics of a rotating heated flat plate surface with constant heat flux when a normal water jet is impinging on this surface. The effects of jet Reynolds number, rotating Reynolds number are investigated while the distance between the nozzle and the flat plate is set fixed. As a result, correlations to relate the local Nusselt number to the local rotational Reynolds number, jet Prandtl number and the dimensionless radial position are presented.

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A Study of Mixed Convection on a Flat Plate with an Unheated Starting Length (비가열부가 있는 평판에서의 혼합대류에 관한 연구)

  • 김민수;강영규;백병준;박복춘
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.5
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    • pp.1304-1312
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    • 1993
  • The buoyancy effects on mixed convection heat transfer over a flat plate surface with unheated starting length is reported. The governing equations are solved by a finite difference method using Patankar scheme and the solution was numerically obtained for various mixed convection parametr $Gr_{x}/Re_{x}^3$, and Prandtl number of 0.7 Local heat flux was measured by using Schilieren Interferometer. The local heat transfer results show that the presence of the unheated starting length can significantly accentuate the effects of buoyancy. The degree of accentuation of the buoyancy effects is strongly influenced by the magnitude of $Gr_{x}/Re_{x}^3$. When the parameter is larger than the order of $10^{-3}$, the contribution of natural convection to the heat transfer coefficients increased significantly due to the unheated starting length. In contrast, when $Gr_{x}/Re_{x}^3$ is smaller then about $10^{-5}$ , the buoyancy contribution is essentially unaffected by the unheated starting length. The shape of the velocity profile is also found to be highly responsive to the interaction between the buoyancy and the starting length.

The Throughflow Effects on Natural Convection in Horizontal Porous Layer (수평 다공층에서 수직 관통류가 자연대류 열전달에 미치는 영향에 관한 연구)

  • 서석진
    • Journal of Energy Engineering
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    • v.7 no.2
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    • pp.209-215
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    • 1998
  • This paper investigated the vertical throughflow effects on natural convection due to heating from below in horizontal porous layer. The motion of the fluid in the porous layer is governed by Brinkman-Darcy equation. And compared Critical Rayleigh number in case of throughflow with no throughflow. Investigated Nusslet number, isothermalline and flow with the variation of the strength of throughflow in a constant Rayleigh number. In the numerical analysis, flow is assumed to be two-dimensional and unsteady. The numerical scheme used is a finite-difference method. In the experimental study, Temperature distribution was measured by use of Liquid Crystal film. As a results, indicated that throughflow influences largely on the temperature field and as the strength of throughflow increased, unstability of natural convection decreased. Also it could predict the strength of natural convection with the measured Nusselt number.

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Finite Element Analysis of Natural Convection of Fluids with Low Prandtl Number in a Square Enclosure (유한요소법을 이용한 정방형 밀폐용기내의 플란틀수가 낮은 유체의 자연대류에 관한 연구)

  • 김무현;이진호;강신형;손영석
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.3
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    • pp.541-550
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    • 1988
  • Natural convection in a square enclosure was investigated numerically for low prandtl number fluids using Finite Element Method. In case of Ra=10$^{4}$, 10$^{5}$ and 10$^{6}$ the temperature gradient decreases gradually at the lower end of the hot wall(or at the upper end of the cold wall) as prandtl number decreases in the range of 0.01 .leq. Pr .leq. 10. Maximum heat transfer occurs at a somewhat higher point from the lower end of hot wall(or at somewhat lower point from the upper end of the cold wall) and it draws near to the lower end of the hot wall(or draws near to the upper end of the cold wall) with increasing prandtl number. The flow in the enclosure appears as an Unicell Pattern for Ra .leq. 10$^{4}$ and secondarily flows(or tertiary flows) appears in the core region for Ra .geq. 10$^{5}$ . The line joining the center of secondary cells skewes in a clockwise direction as the Prandtl number decreases.