• Title, Summary, Keyword: Mixed convection

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Quantitative Visualization of Mixed Convection in 3-D Rectangular Channels Using TLC Tracers (액정을 이용한 3차원 사각채널 내 혼합대류의 정량적 가시화)

  • Piao, Ri-Long;Kim, Jeong-Soo;Bae, Dae-Seok
    • Journal of Power System Engineering
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    • v.20 no.6
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    • pp.51-57
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    • 2016
  • Experiment is carried out to investigate the mixed convective flow in three-dimensional horizontal rectangular channels filled with high viscous fluid. The particle image velocimetry(PIV) with thermo-sensitive liquid crystal tracers is used for visualizing and analysis. Quantitative data of temperature and velocity are obtained by applying the color-image processing to a visualized image, and neural network is applied to the color-to-temperature calibration. In this study, the fluid used is silicon oil(Pr=909), the aspect ratio(channel width to heigh) is 4 and Reynolds number is $2{\times}10^{-2}$. From the present study, we can visualize the quantitative temperature and velocity of mixed convective flow in three-dimensional horizontal rectangular channels simultaneously.

Mixed Convection in Channels of an Electronic Cabinet (전자장비 채널에서의 혼합대류에 관한 연구)

  • 이재헌;남평우;박상동;조성환
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.4
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    • pp.771-779
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    • 1989
  • Numerical analysis by SIMPLE algorithm has been performed to predict the characteristics of flow and heat transfer in channels between the printed circuit boards of an electronic cabinet. It is assumed that the electronic parts release uniform heat flux per unit axial length to the cooling air. The air flow between channels is assumed fully developed laminar, incompressible, and mixed convective. In this study, the electronic parts are mounted on both sides of the prinked circuit boards by two kinds of configuration such as the zig-zag and the symmetric one. The Rayleigh numbers ranging from 0 to 10$^{6}$ are considered to predict the characteristics of the main flow and the secondary flow occurred by natural convection, the temperature distribution in channel, the heat transfer rate from heated electronic parts and the increase of friction factor by natural convection. As the results of numerical calculation, several conclusions are drawn as follows. The influence of natural convection on the flow characteristics appears strong when the Rayleigh number is above 10$^{4}$. The main axial flow rate decreases by a half or more at the Rayleigh number of 10$^{6}$ . Although the friction factor increases as Rayleigh number increases, the increasing rate of heat transfer is higher than that of the friction factor. The cooling efficiency of the zig-zig-configuration is superior to that of the symmetric configuration at same Rayleigh number.

Numerical Study on Combined Heat Transfer in NIR Dryer for Agricultural and Marine Products (근적외선 농수산물 건조기의 복합열전달특성에 관한 수치적 연구)

  • Choi, H.K.
    • Journal of Biosystems Engineering
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    • v.31 no.5
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    • pp.395-402
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    • 2006
  • Mixed heat transfer in an indirected NIR (Near Infrared Ray) dry chamber was investigated numerical analysis. It is Important that the miked heat transfer effects on double parameters which the Reynolds number and the position of emit lamp. Reynolds number are based on the outer diameter of the cylinder range from 103 to $30{\times}105$. Four difference heat transfer regimes of behavior are apparent: forced convection and radiation on the outer surface of the cylinder, pure conduction, pure natural convection and radiation between lamp surface and inner surface of the cylinder. The temperature and flow patterns are illustrated by iso-contour lines for the double parameters. Also presented are results on the convective heat transfer flux and the radiative heat transfer flux as increased with Reynolds number.

The Study of Mixed Convection in a Room with Heated Bottom Surface and various Partitions (밑면이 가열되고 다양한 격판을 가진 실내공간에서의 혼합대류 열전달)

  • Lee, C.J.
    • Solar Energy
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    • v.18 no.1
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    • pp.91-98
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    • 1998
  • The study of mixed convection in a room with heated bottom surface and various partitions has been numerically investigated using a finite volume method. The parameters studied here are, 50$\overline{Nu}=\overline{Nu_n}{\cdot}(1+c(Re/Gr^{1/2})^d)$, where $\overline{Nu_n}$ corresponds to pure natural convextion.

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Effect of variable viscosity on combined forced and free convection boundary-layer flow over a horizontal plate with blowing or suction

  • Mahmoud, Mostafa A.A.
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.11 no.1
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    • pp.57-70
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    • 2007
  • The effects of variable viscosity, blowing or suction on mixed convection flow of a viscous incompressible fluid past a semi-infinite horizontal flat plate aligned parallel to a uniform free stream in the presence of the wall temperature distribution inversely proportional to the square root of the distance from the leading edge have been investigated. The equations governing the flow are transformed into a system of coupled non-linear ordinary differential equations by using similarity variables. The similarity equations have been solved numerically. The effect of the viscosity temperature parameter, the buoyancy parameter and the blowing or suction parameter on the velocity and temperature profiles as well as on the skin-friction coefficient and the Nusselt number are discussed.

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Effect of a Magnetic Field on Mixed Convection of a Nanofluid in a Square Cavity

  • Sheikhzadeh, G.A.;Sebdani, S. Mazrouei;Mahmoodi, M.;Safaeizadeh, Elham;Hashemi, S.E.
    • Journal of Magnetics
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    • v.18 no.3
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    • pp.321-325
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    • 2013
  • The problem of mixed convection in a differentially heated lid-driven square cavity filled with Cu-water nanofluid under effect of a magnetic field is investigated numerically. The left and right walls of the cavity are kept at temperatures of $T_h$ and $T_c$ respectively while the horizontal walls are adiabatic. The top wall of the cavity moves in own plane from left to right. The effects of some pertinent parameters such as Richardson number (ranging from 0.1 to 10), the volume fraction of the nanoparticles (ranging 0 to 0.1) and the Hartmann number (ranging from 0 to 60) on the fluid flow and temperature fields and the rate of heat transfer in the cavity are investigated. It must be noted that in all calculations the Prandtl number of water as the pure fluid is kept at 6.8, while the Grashof number is considered fixed at 104. The obtained results show that the rate of heat transfer increases with an increase of the Reynolds number, while but it decreases with increase in the Hartmann number. Moreover it is found that based the Richardson and Hartmann numbers by increase in volume fraction of the nanoparticles the rate of heat transfer can be enhanced or deteriorated compared to the based fluid.

Heat Transfer Characteristics of Radiation-Mixed Convection in a Three-Dimensional PCB Channel (3차원 PCB 채널내에서의 복사-혼합대류 열전달 특성)

  • Lee, J.H.;Park, K.W.;Pak, H.Y.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.8 no.4
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    • pp.561-575
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    • 1996
  • The interaction of turbulent mixed convection and surface radiation in a three-dimensional channel with the heated blocks is analyzed numerically. Two blocks are maintained at high temperature and the other bottom and horizontal walls are insulated. S-4 method is employed to calculate the effect of the radiative heat transfer. The low Reynolds number k-$\varepsilon$ model proposed by Launder and Sharma is used to estimate the turbulent influence on the heat transfer enhancement. From above modeling, the effects of various channel specifications on the flow and heat transfer characteristics are investigated. The variables used for the present study are Reynolds number, block spacing, the channel height spacing for block and the emissivity. Average Nusselt numbers along the block surfaces are correlated and presented in terms of Reynolds number, emissivity and dimensionless geometric parameters. For the range of conditions in this study, average Nusselt numbers along the block surfaces are strongly influenced by the Reynolds numbers and channel height spacing for block but weakly influenced by the block spacing and the emissivity of the adiabatic walls.

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NON LINEAR VARIABLE VISCOSITY ON MHD MIXED CONVECTION HEAT TRANSFER ALONG HIEMENZ FLOW OVER A THERMALLY STRATIFIED POROUS WEDGE

  • Kandasamy, R.;Hashim, I.;Ruhaila, K.
    • Journal of applied mathematics & informatics
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    • v.26 no.1_2
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    • pp.161-176
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    • 2008
  • The effect of variable viscosity on MHD mixed convection Hiemenz flow over a thermally stratified porous wedge plate has been studied in the presence of suction or injection. The wall of the wedge is embedded in a uniform Darcian porous medium in order to allow for possible fluid wall suction or injection and has a power-law variation of the wall temperature. An approximate numerical solution for the steady laminar boundary-layer flow over a wall of the wedge in the presence of thermal diffusion has been obtained by solving the governing equations using numerical technique. The fluid is assumed to be viscous and incompressible. Numerical calculations are carried out for different values of dimensionless parameters and an analysis of the results obtained shows that the flow field is influenced appreciably by the magnetic effect, variable viscosity, thermal stratification and suction / injection at wall surface. Effects of these major parameters on the transport behaviors are investigated methodically and typical results are illustrated to reveal the tendency of the solutions. Comparisons with previously published works are performed and excellent agreement between the results is obtained.

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A study on the mixed-convection heat transfer characteristics of a simulated module on the bottom in the inclined channel (경사진 채널밑면에 탑재된 모사모듈의 혼합대류열전달 특성 연구)

  • Ryu, Kap-Jong;Lee, Jin-Ho;Jang, Jun-Young
    • Proceedings of the KSME Conference
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    • pp.433-439
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    • 2001
  • An experimental study was carried out on the characteristics of the mixed-convection heat transfer from a protruding heat source module which had uniform heat flux and was located on a flat plate in the inclined channel. The effects of the inclined channel(${\varphi}=0{\sim}90^{\circ}$) was studied for the input power($Q=3,\;7W$) and inlet air velocities($V_{i}=0.1{\sim}0.9m/s$). Experimental results indicate that the input power was most effective parameter on the temperature differences between inlet air and module. The effects of the inclined angle was negligible when the inlet velocities were above 0.5m/s and 0.9m/s at Q = 3W, 7W respectively. As the inclined angle of the channel increases, the temperatures of the module are decreased. So we obtained the best condition on the adiabatic board at the vertical channel.

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An Experiment and Numerical Analysis of Mixed Convection in a Rectangular Space with Variable Partition (가변 격판을 갖는 사각공간 내의 혼합대류에 대한 실험과 수치해석)

  • 이광성;신재호;이중섭;정한식;정효민
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.12
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    • pp.1230-1235
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    • 2001
  • The laminar convection heat transfer in a ventilated space with various horizontal partitions was studied numerically and experimentally. The experimental results by holographic interferometer showed good agreements with the numerical results. For the numerical study, the governing equations were solved by using a finite volume method for $46.6\leqRe\leq1332,\;1460\leqGr\leql1585$, Pr=0.71 and the variations of partition lengths. The isotherms and velocity vectors have been represented for various parameters. As the length of partition increases, the convection heat transfer decreases. Based on the numerical data, a correlation was obtained for the dimensionless mean Nusselt number in terms of $Gr/Re^2$. In the region of $Gr/Re^2$<1, the mean Nusselt number was very small, but in the region of $Gr/Re^2\geq1$, the mean Nusselt number was constant.

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