• Title/Summary/Keyword: Mixed Convection

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A Quantitative Visualization of Mixed Convection in Parallel Plates Using PIV (PIV를 이용한 평행평판 내의 혼합대류의 정량적 가시화)

  • 박일용;배대석
    • Journal of Advanced Marine Engineering and Technology
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    • v.28 no.3
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    • pp.509-515
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    • 2004
  • The PIV(Particle Image Velocimetry) with liquid crystal tracers is used for visualizing and analysis of the mixed convection in the parallel plates with the upper part cooled and the lower part heated. It is found that the flow pattern of mixed convection in the parallel plates can be classified into three patterns which was affected by Reynolds number. Also, the periodic nature is confirmed, and visualized in experiment.

Direct Numerical Simulation of Turbulent Mixed Convection in Heated Vertical Annulus (수직 동심 환형관 내의 난류혼합대류 현상에 관한 직접수치모사)

  • Jun, Yong-Joon;Bae, Joong-Hun;Yoo, Jung-Yul
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.33 no.9
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    • pp.674-681
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    • 2009
  • Turbulent mixed convection in heated vertical annulus is investigated using Direct Numerical Simulation (DNS) technique. The objective of this study is to find out the effect of buoyancy on turbulent mixed convection in heated vertical annulus. Downward and upward flows with bulk Reynolds number 8500, based on hydraulic diameter and mean velocity, have been simulated to investigate turbulent mixed convection by gradually increasing the effect of buoyancy. With increased heat flux, heat transfer coefficient first decreases and then increases in the upward flow due to the effect of buoyancy, but it gradually increases in downward flow. The mean velocity and temperature profiles can not be explained by the wall log laws due to the effect of buoyancy, too. All simulation results are in good quantitative agreement with existing numerical results and in good qualitative agreement with existing experimental results.

Direct numerical simulation of turbulent mixed convection in heated vertical annulus (수직 동심 환형관 내의 난류혼합대류 현상에 관한 직접수치모사)

  • Jun, Yong-Joon;Bae, Joong-Hun;Yoo, Jung-Yul
    • Proceedings of the KSME Conference
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    • pp.2759-2764
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    • 2008
  • Turbulent mixed convection in heated vertical annulus is investigated using Direct Numerical Simulation (DNS) technique. The objective of this study is to find out the effect of buoyancy on turbulent mixed convection in heated vertical annulus. Downward and upward flows with bulk Reynolds number 8500, based on hydraulic diameter and mean velocity, have been simulated to investigate turbulent mixed convection by gradually increasing the effect of buoyancy. With increased heat flux, heat transfer coefficient first decreases and then increases in the upward flow due to the effect of buoyancy, but it gradually increases in downward flow. The mean velocity and temperature profiles can not be explained by the wall log laws due to the effect of buoyancy, too. All simulation results are in good quantitative agreement with existing numerical results and in good qualitative agreement with existing experimental results.

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Validity Review of Mixed Convection Flow Regime Map in Vertical Cylinders (수직 원형관내 혼합대류 유동영역지도의 유효성 검토)

  • Kang, Gyeong-Uk;Kim, Hyoung-Jin;Yoon, Si-Tae;Chung, Bum-Jin
    • Journal of Energy Engineering
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    • v.23 no.3
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    • pp.27-35
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    • 2014
  • The existing flow regime map on mixed convection in vertical cylinders was investigated through an analysis of original literatures and its re-formation. The original literatures related to the existing map were reviewed. Using the investigated data and heat transfer correlations, the map was redrawn independently, and compared with the existing map. The redrawn map showed that mixed convection regime was not curved lines but straight lines and the transition regime was unable to be reproduced. Unlike the existing map with a little data, there are lots of data in the redrawn map. The reviews revealed that the existing map used the data selectively among the experimental and theoretical results, and a detailed description for lines forming mixed convection and transition regime was not provided. While considerable studies on mixed convection have been performed since that of Metais and Eckert, the existing map has still been used as the best method to distinguish natural, forced and mixed convection regime.

EXISTENCE AND NON-UNIQUENESS OF SOLUTION FOR A MIXED CONVECTION FLOW THROUGH A POROUS MEDIUM

  • Hammouch, Zakia;Guedda, Mohamed
    • Journal of applied mathematics & informatics
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    • v.31 no.5_6
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    • pp.631-642
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    • 2013
  • In this paper we reconsider the problem of steady mixed convection boundary-layer flow over a vertical flat plate studied in [6],[7] and [13]. Under favorable assumptions, we prove existence of multiple similarity solutions, we study also their asymptotic behavior. Numerical solutions are carried out using a shooting integration scheme.

Mixed-Convection in an Annulus Between Co-Rotating Horizontal Cylinders (동시 회전하는 수평 실린더 내 환상공간에서의 혼합대류)

  • Lee, Gwan-Su;Kim, Yang-Hyeon;Im, Gwang-Ok
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.4
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    • pp.622-628
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    • 2002
  • Numerical analysis has been carried out for two-dimensional steady and unsteady mixed convection in the annulus between co-rotating horizontal cylinders with a heated inner cylinder. The ratio of annulus gap($\sigma$) is taken from 1 to 10 and the order of mixed-convection parameter B(=Gr/(1+Re)$^2$) varies from 10$^4$to $10^0$. The flow patterns over this parameter range are steady multicellular, oscillatory multicellular or steady unicellular. The addition of co-rotating of both cylinders stabilizes the flow in the annulus and weakens the unsteadiness. Even in the large values of rotating parameter such as of $10^0$/($\sigma$=2) and 10$^2$($\sigma$=10), the flow pattern becomes asymptotic to the steady unicellular flow, like as in the rigid-body rotating flow.

An Experimental Investigation of Unsteady Mixed Convection in a Horizontal Channel with Cavity Using Thermo-Sensitive Liquid Crystals

  • Bae, Dae-Seok;Cai, Long-Ji;Kim, Eun-Pil
    • Journal of Advanced Marine Engineering and Technology
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    • v.33 no.7
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    • pp.987-993
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    • 2009
  • An experimental study is performed to investigate unsteady mixed convection in a horizontal channel with a heat source. Particle image velocimetry (PIV) with thermo-sensitive liquid crystal (TLC) tracers is used for visualization and analysis. This method allows simultaneous measurement of velocity and temperature fields at a given instant of time. Quantitative data of the 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. It is found that the periodic flow of mixed convection in a cavity appears at very low Reynolds numbers (Re<0.4), and the period decreases with increasing Reynolds numbers and increases with increasing aspect ratio.

Flow Visualization and Measurement of Velocity and Temperature in Parallel Plates

  • Piao, R.-L;Bae, D.-S
    • Journal of Advanced Marine Engineering and Technology
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    • v.28 no.2
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    • pp.277-284
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    • 2004
  • This paper describes the influence of through-flow on the mixed convection in a parallel plates with the upper part is cooled and the lower part heated. When forced convection is imposed on natural convection, it is found that the flow pattern of mixed convection in the parallel plates can be classified into three patterns which were affected by Reynolds number. In such a mixed convection, the flow pattern plays an important role in the heat transfer process. In this study, thermo-sensitive liquid crystal suspension method is employed, then the visualization image acquired through the above method is processed by the color image processing technique and the two-dimensional velocity vector and temperature configuration are measured simultaneously.

3-D Numerical Analysis on a low Reynolds Number Mixed Convection in a Horizontal Rectangular Channel (수평 사각채널 내 저 레놀즈수 혼합대류 유동의 3차원 수치해석)

  • Piao, Ri-Long;Bae, Dae-Seok
    • Proceedings of the Korean Society of Marine Engineers Conference
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    • pp.210-215
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    • 2005
  • A three-dimensional numerical simulation is performed to investigate on a low Reynolds number mixed convection in a horizontal rectangular channel with the upper part cooled and the lower part heated uniformly. The three-dimensional governing equations are solved using a finite volume method. For convective term, the central differencing scheme is used and for the pressure correction, the PISO algorithm is used. Solutions are obtained for A=4, Pr=0.72, 10, 909, the Reynolds number ranging from $2.1{\times}10^{-2}$ to $1.2{\times}10^{-1}$, the Rayleigh number is $3.5{\times}10^4$. It is found that vortex roll structures of mixed convection in horizontal rectangular channel can be classified into three roll structures which affected by Prandtl number and Reynolds number.

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Characteristics of the Mixed Convection Flow and Heat Transfer in a Channel with Open Cavity (개방된 캐비티를 가진 채널 내에서의 혼합대류 유동과 열전달 특성)

  • Ko, Y.C.;Bae, D.S.;Kim, N.S.
    • Journal of Power System Engineering
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    • v.11 no.4
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    • pp.56-64
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    • 2007
  • A numerical simulation is carried out mixed convection in horizontal channel with a heat source from below of rectangular cavity. Finite volume method was employed for the discretization and PISO algorithm was used for calculating pressure term. The parameters governing the problem are the Reynolds number ($10^{-2}{\leq}Re{\leq}50$), the Rayleigh number ($10^3{\leq}Ra{\leq}2.06{\times}10^5$), the Prandtl number ($0.72{\leq}Pr{\leq}909$), the aspect ratio ($0.5{\leq}AR=W/H{\leq}2$) and the angle of inclination ($0^{\circ}{\theta}60^{\circ}$). Mean Nusselt number distributions were obtained and effect of Reynolds number, Rayleigh number and Prandtl number on mixed convection in the horizontal channel with rectangular cavity were investigated.

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