• Title, Summary, Keyword: Mixed convection

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On the performance of heat absorption/generation and thermal stratification in mixed convective flow of an Oldroyd-B fluid

  • Hayat, Tasawar;Khan, Muhammad Ijaz;Waqas, Muhammad;Alsaedi, Ahmed
    • Nuclear Engineering and Technology
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    • v.49 no.8
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    • pp.1645-1653
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    • 2017
  • This investigation explores the thermally stratified stretchable flow of an Oldroyd-B material bounded by a linear stretched surface. Heat transfer characteristics are addressed through thermal stratification and heat generation/absorption. Formulation is arranged for mixed convection. Application of suitable transformations provides ordinary differential systems through partial differential systems. The homotopy concept is adopted for the solution of nonlinear differential systems. The influence of several arising variables on velocity and temperature is addressed. Besides this, the rate of heat transfer is calculated and presented in tabular form. It is noticed that velocity and Nusselt number increase when the thermal buoyancy parameter is enhanced. Moreover, temperature is found to decrease for larger values of Prandtl number and heat absorption parameter. Comparative analysis for limiting study is performed and excellent agreement is found.

A Study of a Simultaneous Filling and Solidification During Casting Process (충전과 상변화 현상을 포함한 주조과정에 대한 연구)

  • Im, lk-Tae;Kim, Woo-Seung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.23 no.8
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    • pp.987-996
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    • 1999
  • An algorithm for modeling the filling of metal into a mold and solidification has been developed. This algorithm uses the implicit VOF method for a filling and a general implicit source-based method for solidification. The model for simultaneous filling and solidification is applied to the two-dimensional filling and solidification of a square cavity. The effects of the wall temperature and gate position on the solidification are examined. The mixed natural convection flow and residual flow resulting from the completion of a filling are included in this study to investigate the coupled effects of the filling and natural convection on solidification. Two different filling configurations (assisting flow and opposite flow due to the gate position) are analysed to study the effects of residual flow on solidification. The results clearly show the necessity to carry out a coupled filling and solidification analysis including the effect of natural convection.

Incompressible smoothed particle hydrodynamics modeling of thermal convection

  • Moballa, Burniadi;Chern, Ming-Jyh;Odhiambo, Ernest
    • Interaction and multiscale mechanics
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    • v.6 no.2
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    • pp.211-235
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    • 2013
  • An incompressible smoothed particle hydrodynamics (ISPH) method based on the incremental pressure projection method is developed in this study. The Rayleigh-B$\acute{e}$nard convection in a square enclosure is used as a validation case and the results obtained by the proposed ISPH model are compared to the benchmark solutions. The comparison shows that the established ISPH method has a good performance in terms of accuracy. Subsequently, the proposed ISPH method is employed to simulate natural convection from a heated cylinder in a square enclosure. It shows that the predictions obtained by the ISPH method are in good agreements with the results obtained by previous studies using alternative numerical methods. A rotating and heated cylinder is also considered to study the effect of the rotation on the heat transfer process in the enclosure space. The numerical results show that for a square enclosure at, the addition of kinetic energy in the form of rotation does not enhance the heat transfer process. The method is also applied to simulate forced convection from a circular cylinder in an unbounded uniform flow. In terms of results, it turns out that the proposed ISPH model is capable to simulate heat transfer problems with the complex and moving boundaries.

Mixed Convection Transport from a Module on the Bottom Surface of Three Dimensional Channel (3차원 채널 밑면에 탑재된 모듈로부터의 혼합대류열전달)

  • Lee, Jin-Ho;Park, Sang-Hee;Riu, Kap-Jong;Bang, Chang-Hoon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.5
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    • pp.632-639
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    • 2000
  • Conjugate heat transfer from a heat generating module ($31{\times}31{\times}7mm^3$) bonded through the module support on the floor of a parallel-plate channel(20mm high, 400mm wide, and 800mm long) to mixed convective air flow(0.2${\sim}$0.9m/s) is studied experimentally. The input power to the module is changed in a range 1.0${\sim}$4.5W, the floor thickness 0.2${\sim}$5mm, and the thermal resistance of module support, Rc:=0.06, 1.03 and 82.0K/W. Thermal conductance(Uc) of the board and convective thermal conductance($U_A$) from the module were derived, and the effect of V; Rc and t on Uc was investigated. It is found that the conjugate conductance (Uc) and the conductive heat transfer ratio ($Q_B$/Q) depend on the thermal resistance of the module support, the air velocity and the board thickness. The change of the module support resistance and the board thickness helps to elucidate the relative significance of heat transfer paths through the module support, the board, and from the board surface to the air. Additional information is investigated about the dependence of the heat transfer rate on the mixed convection parameter.

Three-Dimensional Numerical Study on the Vortex Flow in a Horizontal Channels with High Viscous Fluid (수평채널 내 고 점성유체의 볼텍스 유동에 관한 3차원 수치해석(1))

  • Piao, Ri-Long;Kim, Jeong-Soo;Bae, Dae-Seok
    • Journal of Power System Engineering
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    • v.18 no.3
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    • pp.79-86
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    • 2014
  • Mixed convective vortex flow in the three-dimensional rectangular channel filled with high viscous fluid(Pr=909) is investigated computationally under various operating conditions. The Reynolds number is varied from 0 to $5{\times}10^{-1}$, the Rayleigh number from $10^3$ to $5{\times}10^4$. The three-dimensional governing equations are discretized using the finite volume method. The effects of Reynolds number and Rayleigh number are presented and discussed. From a parametric study, it is found that vortex flow pattern of mixed convection in rectangular channels can be classified into three flow patterns basically, but the new vortex flow structures containing wave rolls are found, which are affected by Rayleigh number and Reynolds number. From this results, we can draw a flow regime map to delineate various vortex flow patterns in the high viscosity fluid mixed convective flow.

An experimental study of freezing phenomenon with supercooled water region (과냉각을 동반하는 물의 동결현상에 관한 실험)

  • Yoon, J.I.;Kim, J.D.;Kum, J.S.;Chu, M.S.;Kamata, Y.;Kato, T.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.9 no.2
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    • pp.104-111
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    • 1997
  • The freezing phenomenon of saturated water with the supercooled region in a horizontal circular cylinder has been studied experimentally by using the holographic real time interferometry technique. From the experiments, it was found that there were three types of freezing patterns. The first is the annular ice layer growing from the cylinder surface at a high cooling rate; the next is the asymmetric ice layer at a moderate cooling rate; and the last is the instantaneous ice layer growth over the full region at lower cooling rate. As the water was coolde from room temperature to the subfreezing point passing through the density inversion point, the freezing pattern was largely affected by the inversion phenomenon, which had much effected the free convection and was susceptible to influences from the cooling rate. When the cooling rate is high, supercooling energy is released before the water is sufficientry mixed by free convection. On the other hand, when the cooling rate is low, there is much time for the water to be mixed by free convection. This seems to be the reason why the different ice layer growths occur.

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AN UPSTREAM PSEUDOSTRESS-VELOCITY MIXED FORMULATION FOR THE OSEEN EQUATIONS

  • Park, Eun-Jae;Seo, Boyoon
    • Bulletin of the Korean Mathematical Society
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    • v.51 no.1
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    • pp.267-285
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    • 2014
  • An upstream scheme based on the pseudostress-velocity mixed formulation is studied to solve convection-dominated Oseen equations. Lagrange multipliers are introduced to treat the trace-free constraint and the lowest order Raviart-Thomas finite element space on rectangular mesh is used. Error analysis for several quantities of interest is given. Particularly, first-order convergence in $L^2$ norm for the velocity is proved. Finally, numerical experiments for various cases are presented to show the efficiency of this method.