• 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.

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.

Analysis of mixed convective laminar flow and heat transfer about a sphere (혼합대류에 의한 구 주위의 충류유동 및 열전달 해석)

  • 이준식;김택영
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.2
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    • pp.345-353
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    • 1987
  • An analysis is performed to study flow and heat transfer characteristics of mixed free and forced convection about a sphere. Nonsimilar boundary layer equations which are valid over the entire regime of mixed convection are derived in terms of the mixed convection parameter, Gr/Re$^{2}$, through a dimensional analysis. The transformed conservation equations are solved by a finite difference method for the whole range of mixed convection regime. Numerical results for fluids having the Prandtl number 0.7 and 7 are presented. As the mixed convection parameter increases, the local friction coefficient and local heat transfer coefficient increases as well. For small Prandtl number, the friction coefficient is larger, while for large Prandtl number, the heat transfer coefficient is larger. Natural convection effect on the forced flow is more sensitive for small Prandtl number fluid. Flow separation migrates rearward as an increase in the mixed convection parameter. For small Prandtl number, the buoyancy effect is relatively small so that the flow separation occurs earlier.

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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A SPLIT LEAST-SQUARES CHARACTERISTIC MIXED ELEMENT METHOD FOR SOBOLEV EQUATIONS WITH A CONVECTION TERM

  • Ohm, Mi Ray;Shin, Jun Yong
    • East Asian mathematical journal
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    • v.35 no.5
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    • pp.569-587
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    • 2019
  • In this paper, we consider a split least-squares characteristic mixed element method for Sobolev equations with a convection term. First, to manipulate both convection term and time derivative term efficiently, we apply a characteristic mixed element method to get the system of equations in the primal unknown and the flux unknown and then get a least-squares minimization problem and a least-squares characteristic mixed element scheme. Finally, we obtain a split least-squares characteristic mixed element scheme for the given problem whose system is uncoupled in the unknowns. We prove the optimal order in $L^2$ and $H^1$ normed spaces for the primal unknown and the suboptimal order in $L^2$ normed space for the flux unknown.

A Numerical Study on Mixed Convection in Boundary Layer Flows over Inclined Surfaces (경사진 평판 주위에서 경계층유동의 혼합대류에 관한 연구)

  • 김동현;최영기
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.3
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    • pp.725-733
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    • 1990
  • An analysis of laminar mixed convection flow adjacent to the inclined flat surface which is subjected to a uniform temperature in a uniform free stream is performed. Nonsimilar boundary layed equation are derived by using the mixed convection parameters such that smooth transition from the purely forced convection limit to the purely free convection limit is possible. The governing equations are solved by a finite difference method using the coupled box scheme of sixth order. Numerical results are presented for prandtl numbers of 0.7 and 7 with the angle of inclination ranging from 0 to 90 degree from the vertical. The velocity distributions for the buoyancy assisting flow exhibit a significant overshoot above the free stream value in the region of intense mixed convection and the velocity field is found to be more sensitive to the buoyancy effect than the temperature field. The separation point near the wall was obtained for the buoyancy opposing flow. The local Nusselt number increases for buoyancy assisting flow and decreases for opposing flow with increasing value of the local Grashoff number in the mixed convection parameter. For large Prandtl number, the Nusselt number and the friction factor decrease significantly near the separation point. Present numerical predictions are in good agreement with recent experimental results by Ramachandran.

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 a Horizontal Annulus with a Rotating Cylinder (하나의 실린더가 회전하는 수평 환형 공간에서의 혼합 대류)

  • Yoo Joo-Sik;Ha Dae-Hong
    • Journal of computational fluids engineering
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    • v.6 no.3
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    • pp.1-9
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    • 2001
  • Mixed convection in a horizontal annulus is considered, and the effect of a forced flow on the natural convective flow is investigated. The inner cylinder is hotter than the outer cylinder, and the outer cylinder is rotating with constant angular velocity with its axis at the center of the annulus. The unsteady streamfunction-vorticity equation is solved with a finite difference method. For the fluid with Pr=0.7, there appear flows with two eddies, one eddy, or no eddy according the Rayleigh and Reynolds numbers. The rotation of the outer cylinder reduces the heat transfer rate at the wall of the annulus. The oscillatory multicellular flow of a low Prandtl number fluid with Pr=0.01 can be effectively suppressed by the forced flow.

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