• Journal of Power System Engineering
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• v.10 no.2
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• pp.29-35
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• 2006

Two-dimensional numerical simulation has been performed to investigate mixed convection heat transfer between inclined parallel plates with bottom-heated and top-cooled uniformly. The ratio of parallel plate length to height is 9.33, Prandtl number is 909(that of silicone oil at 298K) and Rayleigh number is 8600. In the ranges of the Reynolds number Re from 0 to 1.8 and the angle of inclination ${\theta}$ from 0 to 90 degree. The governing equations are discretized using the finite volume method. In this study, the effects of the Reynolds number, the angle of inclination, and the local and mean Nusselt numbers are presented and discussed. It is found that the periodic flow of mixed convection between inclined parallel plates is shown at $0^{\circ}{\leq}\;{\theta}<30^{\circ},\;Re<0.063$, and the flow pattern can be classified into three patterns which depend on Reynolds number and the angle of inclination. The minimum average Nusselt numbers occur at Re=0.05 regardless of the angle of inclination.

• Journal of Power System Engineering
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• v.19 no.4
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• pp.36-42
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• 2015

TMixed convective flow in a bottom heated and top cooled rectangular channel can be significantly affected by the channel aspect ratio, Prandtl number, Reynolds number, Rayleigh number and angle of inclination. In such a mixed convection, the flow pattern plays an important role in various technological processes. In this study, a numerical investigation is carried out to explore mixed convection in a three-dimensional rectangular channel with bottom heated and top cooled uniformly. The three-dimensional governing equations are discretized using the finite volume method. In the range of low Reynolds number($0{\leq}Re{\leq}9.6{\times}10^{-2}$), the effects of the aspect ratio($2{\leq}AR{\leq}12$) and Gr/Re are presented and discussed. The longitudinal roll number in the channel is increased with increasing aspect ratio, and the roll number induced, regardless of the aspect ratio number, is even in the range of aspect ratios between 2 and 12, New vortex flow structure containing inclined longitudinal rolls is found, which is affected by aspect ratio and Reynolds number. The ratio Gr/Re is used to check the relative magnitudes of forced and natural convection in the mixed convective flow of high viscous fluid.

• 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.

• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.48-54
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• 1998

Three-dimensional incompressible Navier-Stokes equations have been solved by the node-centered finite volume method with unstructured hybrid grids. The pressure-velocity coupling is handled by the artificial compressibility algorithm and convective fluxes are obtained by Roe's flux difference splitting scheme with linear reconstruction of the solutions. Euler implicit method is used for time-integration. The viscous terms are discretised in a manner to handle any kind of grids such as tetrahedra, prisms, pyramids, hexahedra, or mixed-element grid. The numerical efficiency and accuracy of the present method is critically evaluated for several example problems.

• The KSFM Journal of Fluid Machinery
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• v.11 no.5
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• pp.50-56
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• 2008

Metal cutting operations involve generation of heat due to friction between the tool and the pieces. This heat needs to be carried away otherwise it creates white spots. To reduce this abnormal heat cutting fluid is used. Cutting fluid also has an important role in the lubrication of the cutting edges of machine tools and the pieces they are shaping, and in sluicing away the resulting swarf. As a cutting fluid, water is a great conductor of heat but is not stable at high temperatures, so to improve stability an emulsion type mixed fluid with water and oil is often used. It is pumped over the cutting site of cutting machines as a state of atomized water droplet coated with oil by using jet. In this paper, to develop cutting fluid supplying nozzle to obtain ultra thin oil film for coating water droplet, a numerical analysis of three dimensional mixed fluid Jet through multi-stage nozzle was carried out by using a finite volume method. Jet flow characteristics such as nozzle exit velocity, development of mixing region, re-entrance and jet intensity were analyzed. Detailed mixing process of fluids such as air, water and oil in the nozzle were also investigated. It is easy to understand complex flow pattern in multi-stage nozzle. Important flow Information for advance design of cutting fluid supplying nozzle was drawn.

• Computers and Concrete
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• v.19 no.5
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• pp.579-588
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• 2017

Creep and shrinkage are the main types of volume change with time in concrete. These changes cause deflection, cracking and stresses that affect durability, serviceability, long-term reliability and structural integrity of civil engineering infrastructure. Although laboratory test may be undertaken to determine the deformation properties of concrete, these are time-consuming, often expensive and generally not a practical option. Therefore, relatively simple empirically design code models are relied to predict the creep strain. This paper reviews the accuracy of creep and shrinkage predictions of reinforced concrete (RC) shear walls structures strengthened with carbon fibre reinforced polymer (CFRP) plates, which is characterized by a widthwise varying fibre volume fraction. This review is yielded by three commonly used international "code type" models. The assessed are the: CEB-FIP MC 90 model, ACI 209 model and Bazant & Baweja (B3) model. The time-dependent behavior was investigated to analyze their seismic behavior. In the numerical formulation, the adherents and the adhesives are all modelled as shear wall elements, using the mixed finite element method. Several tests were used to demonstrate the accuracy and effectiveness of the proposed method. Numerical results from the present analysis are presented to illustrate the significance of the time-dependency of the lateral displacements and eigenfrequencies modes.

• Journal of computational fluids engineering
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• v.3 no.2
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• pp.17-26
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• 1998

The three-dimensional incompressible Navier-Stokes equations have been solved by a node-centered finite volume method with unstructured hybrid grids. The pressure-velocity coupling is handled by the artificial compressibility algorithm and convective fluxes are obtained by Roe's flux difference splitting scheme with linear reconstruction of the solutions. Euler implicit method with Jacobi matrix solver is used for the time-integration. The viscous terms are discretised in a manner to handle any kind of grids such as tetragedra, prisms, pyramids, hexahedra, or mixed-element grid. Inviscid bump flow is solved to check the accuracy of high order convective flux discretisation. And viscous flows around a circular cylinder and a sphere are studied to show the efficiency and accuracy of the solver.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.4
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• pp.495-503
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• 2001

In a functionally graded materials(FGM), two constituent material particles are mixed up according to a specific volume fraction distribution so that its thermoelastic behavior is definitely characterized by such a material composition distribution. Therefore, the designer should determine the most suitable volume fraction distribution in order to design a FGM that optimally meets the desired performance against the given constraints. In this paper, we address a numerical optimization procedure, with employing interior penalty function method(IPFM) and FDM, for optimizing 2D volume fractions of heat-resisting FGMs composed of metal and ceramic. We discretize a FGM domain into finite number of homogenized rectangular cells of single design variable in order for the optimization efficiency. However, after the optimization process, we interpolate the discontinuous volume fraction with globally continuous bilinear function in order to enforce the continuity of volume fraction distributions.

• Journal of Welding and Joining
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• v.15 no.6
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• pp.105-115
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• 1997

A numerical study is performed to predict the thermal response of a detailed card assembly during infrared reflow soldering. The card assembly is exposed to discontinuous infrared panel heater temperature distributions and high radiative/convective heating and cooling rates at the inlet and exit of the oven. The convective, radiative and conduction heat transfer within the reflow oven as well as within the card assembly are simulated and the predictions illustrate the detailed thermal responses. The predictions show that mixed convection plays an important role with relatively high frequency effects attributed to buoyancy forces, however the thermal response of the card assembly is dominated by radiation. The predictions of the detailed card assembly thermal response can be used to select the oven operating conditions to ensure proper solder melting and minimization of thermally induced card assembly tresses and warpage.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.1
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• pp.95-104
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• 2003

The objective of this work is to investigate the turbulent reacting flow in a three dimensional combustor with emphasis on thermal NO emission through a numerical simulation. Flow field is analyzed using the SIMPLE method which is known as stable as well as accurate in the combustion modeling, and the finite volume method is adopted in solving the radiative transfer equation. In this work, the thermal characteristics and NO emission in a three dimensional combustor by changing parameters such as equivalence ratio and inlet swirl angle have investigated. As the equivalence ratio increases, which means that more fuel is supplied due to a larger inlet fuel velocity, the flame temperature increases and the location of maximum temperature and thermal NO has moved towards downstream. In the mean while, the existence of inlet swirl velocity makes the fuel and combustion air more completely mixed and burnt in short distance. Therefore, the locations of the maximum reaction rate, temperature and thermal NO were shifted to forward direction compared with the case of no swirl.