• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.77-82
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• 2006

Evaluation of the elliptic blending turbulence model (EBM) together with the two-layer model, shear stress transport (SST) model and elliptic relaxation model (V2-F) is performed for a better prediction of natural convection and thermal stratification. For a natural convection problem the models are applied to the prediction of a natural convection in a rectangular cavity and the computed results are compared with the experimental data. It is shown that the elliptic blending model predicts as good as or better than the existing second moment differential stress and flux model for the mean velocity and turbulent quantities. For thermal stratification problem the models are applied to the thermal stratification in the upper plenum of liquid metal reactor. In this analysis there exist much differences between the turbulence models in predicting the temporal variation of temperature. The V2-F model and EBM better predict the steep gradient of temperature at the interface of thermal stratification, and the V2-F model and EBM predict properly the oscillation of temperature. The two-layer model and SST model fail to predict the temporal oscillation of temperature.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.1
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• pp.64-72
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• 1989

Laminar natural convection heat transfer from a horizontal heat exchanger tube with one infinitely long vertical plate fin has been studied by a finite-difference numerical procedure. In predicting convective heat transfer from a circular tube, the thermal boundary condition at solid fluid interface is usually assumed to be isothermal. However, in reality, the thermal boundary condition is not isothermal, and the tube has the thickness and the conductivity. So the temperature at the interface is not known a priori to the calculation. This problem has the conjugate phenomena which occur between the tube conduction and external natural convection, and between the fin conduction and external natural convection. Numerical results are obtained to determine the effects of the conductivity of solid wall and the thickness of tube wall on heat transfer. It is found that the conduction causes significant influence on the natural convection heat transfer at low K and high ${\delta}$.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.13-14
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• 2003

Two different ${\kappa}-{\varepsilon}-\overline{{\nu}{\nu}}-f$ turbulence models together with the two-layer model are evaluated for natural convection in a rectangular cavity. The numerical problem and accuracy of the turbulence models are discussed. The original $\overline{{\nu}{\nu}}-f$ model suffers from the numerical stiffness problem when used with the segregate solution procedure like the SIMPLE algorithm, and a remedy for this problem is proposed. It is shown that original $\overline{{\nu}{\nu}}-f$ model best predicts the mean velocity, Reynolds stresses and the turbulent heat flux while the modified $\overline{{\nu}{\nu}}-f$ model (N=6) overpredicts the turbulent quantities.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.9 no.2
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• pp.17-27
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• 2005

The problem of the onset stability in an inclined layer of dielectric viscoelastic fluid (Walter's liquid B') is studied. The analysis is made under the simultaneous action of a normal a.c. electric field and the natural convection flow due to uniformly distributed internal heat sources. The power series method used to obtain the eigen value equation which is then solved numerically to obtain the stable and unstable solutions. Numerical results are given and illustrated graphically.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.1
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• pp.161-169
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• 1989

A stability problem on wave instability of natural convection flow along isothermal vertical cylindrical surfaces has been formulated, accounting for the non-parallelism of the basic flow and thermal fields. Then the problem is solved numerically under the simplifying assumption of the parallelism of the basic flow quantities. It is shown that the flow corresponding to the same characteristic boundary layer thickness becomes more stable as the value of the curvature parameter increases. The stability characteristics for Pr=0.7 appear to be more sensitive to the curvature parameter than those for Pr=7.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.2
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• pp.382-390
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• 1992

The problem of natural convection from a vertical fin is solved by coupling the thermal diffusion equation in the fin to the constitutive equations of the ambient medium involving the radiation of the medium. The analysis is accomplished by employing an integral method. The governing equations for the problem are solved by shooting method based on the Runge-Kutta Scheme at Pr= 0.7. For the range of values of the fin parameter and the radiation-conduction parameter in the analysis, the numerical results show that the radiation effects play an important role in the heat transfer and enhance the heat transfer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.3
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• pp.170-177
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• 2009

In the present study, a finite element analysis of conjugate heat transfer problem inside a cavity with a heat-generating conducting body, where constant heat flux is generated, is conducted. A conduction heat transfer problem inside the solid body is automatically coupled with natural convection inside the cavity by using a finite element formulation. A finite element formulation based on SIMPLE type algorithm is adopted for the solution of the incompressible Navier-Stokes equations coupled with energy equation. The proposed algorithm is verified by solving the benchmark problem of conjugate heat transfer inside a cavity having a centered body. Then a conjugate natural heat transfer problem inside a cavity having a heat-generating conducting body with constant heat flux is solved and the effect of the Rayleigh number on the heat transfer characteristics inside a cavity is investigated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.11
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• pp.3686-3694
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• 1996

A numerical investigation of natural convection flow along irregular vertical surfaces is reported. A transformation method is applied to the problem of natural convection under the assumption of a large Grashof number. A vertical wavy surface is used as an example to demonstrate the advantages of the transformation method, and to show the heat transfer mechanism near such surfaces. Surface non-uniformities on the boundary layer flow induced by a constant was temperature, semi-infinite surface are investigated. Also the effects of Prandtl number, flow index, and surface amplitude in Non-Newtonian fluids are discussed. When possible, the comparison of the numerical results shows a good agreement. The amplitude is proportional to the amplitude of a wavy surface. The results demonstrate that the local heat flux along a wavy surface is smaller than that of a flat surface. The frequency of the wavy surface is half that of the local heat transfer rate. The amplitude of the local Nusselt number gradually decreases downstream where the natural convection boundary layer grows thick.

• Journal of computational fluids engineering
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• v.9 no.4
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• pp.1-6
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• 2004

This study investigates the transition of flows in a natural convection problem with periodic wall temperatures of the form, T/sub L/=T₁＋δ Tsinκχ and T/sub L/=T₂＋δ Tsinκχ .The fluid considered is air with P/sub γ/=0.7. In the conduction-dominated regime with a small Rayleigh number, two large cells are formed over one wave length, for all wave numbers. When k≤1.8, the flow becomes unstable with increase of the Rayleigh number, and multicellular convection occurs above a critical Rayleigh number. The flow patterns are classified by the number of eddies over one wave length, and several kinds of transition phenomena, such as 2→3→4, 4→3→2, and 2→4 eddy flow, occur with increase( or decrease) of the Rayleigh number. Dual solutions are found above a critical Rayleigh number, and an anomalous bifurcation is observed.

• Solar Energy
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• v.2 no.1
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• pp.9-16
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• 1982

The problem of transient laminar natural convection in compressible fluid in a rectangular enclosure is considered. The upper and lower boundaries of the enclosure are thermally insulating and the side boundaries are maintained at fixed temperatures. The fluid is considered to be a perfect gas with constant viscosity and thermal conductivity and the formulation differs from the boussinesq simplification in that the effects of variable density are completely retained. The motions are restricted to two dimensions. For incompressible fluid, the natural convection is driven mainly by buoyancy force. But the solutions show that for compressible fluid, the natural convection is driven by pressure and buoyancy forces and the thermally induced motion is acoustic in nature.