• Journal of the Korean Society of Safety
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• v.13 no.2
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• pp.22-29
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• 1998

The natural convection cooling of simulated electronic chips located on a printed circuit board(PCB) has been studied by Computer Aided Engineering(CAE). In CAE, 3-dimensional finite element model of simulated electronic chip was made to accomplish heat transfer analysis at each design stage of a printed circuit boards for thermal optimization. The simulated electronic chips are installed protrudent from the plate about 3mm. The materials the plates are epoxy and aluminum. The results show that the chip with relatively high heat generation rates should not be close to each other. It is found, as well that cooling effect for the aluminum plate is superior to the epoxy plate and location of maximum temperature is significantly influenced by the structure variation of PCB. In developing PCB and electronic chips, it's recommended that CAE is very useful to estimate to the distribution of temperature.

• Steel and Composite Structures
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• v.24 no.3
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• pp.359-367
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• 2017

In this work, transient heat transfer analysis of functionally graded (FG) carbon nanotube reinforced nanocomposite (CNTRC) cylinders with various essential and natural boundary conditions is investigated by a mesh-free method. The cylinders are subjected to thermal flux, convection environments and constant temperature faces. The material properties of the nanocomposite are estimated by an extended micro mechanical model in volume fraction form. The distribution of carbon nanotube (CNT) has a linear variation along the radial direction of axisymmetric cylinder. In the mesh-free analysis, moving least squares shape functions are used for approximation of temperature field in the weak form of heat transform equation and the transformation method is used for the imposition of essential boundary conditions. Newmark method is applied for solution time depended problem. The effects of CNT distribution pattern and volume fraction, cylinder thickness and boundary conditions are investigated on the transient temperature field of the nanocomposite cylinders.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.2
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• pp.217-226
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• 1998

A numerical study has been carried out for two- and three-dimensional buoyant turbulent flow in a stairwell model. The Reynolds-averaged Navier-Stokes and energy equations are solved with the authors'own computer program. Two models by the Boussinesq approximation and the density-gradient form are used for buoyancy terms in the governing equations. Two- and three-dimensional predictions of the velocity and temperature fields are presented and the results are compared with experimental data. Comparisons have also been made in detail with two-dimensional predictions. Two-dimensional and three-dimensional simulations have predicted the overall features of the flow satisfactorily. A better agreement with experiment is achieved with three-dimensional simulations.

• Journal of computational fluids engineering
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• v.7 no.4
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• pp.1-7
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• 2002

The phase-change transformation processes are relevant in many engineering applications. In particular, this phenomenon plays an important role in the extraction and fabrication operations in the metallurgical industry. The control of the heat transfer and fluid flow patterns is important to achieve casting quality and competitive production times. In the present study, a simple finite-element algorithm is developed for solid-liquid phase change problems. Natural convection in the liquid phase due to the temperature dependency of water density is considered by a numerical model. The predictions are compared with measurements by the particle image velocimetry(PIV). to show that the calculation results are in good agreement with the experiment results.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.268-275
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• 2008

The prediction of hydrate pellet decomposition characteristics is required to design the regasification process of GTS (gas to solid) technology, which is considered as an economic alternative for LNG technology to transport natural gas produced from small and stranded gas wells. Mathematical model based on the conservation principles, the phase equilibrium relation, equation of gas state and phase change kinetics was set up and numerical solution procedure employing volume averaged fixed grid formulation and extended enthalpy method are implemented. Initially, porous methane hydrate pellet is at uniform temperature and pressure within hydrate stable region. The pressure starts to decrease with a fixed rate down to the final pressure and is kept constant afterwards while the bounding surface of pellet is heated by convection. The predicted convective heat and mass transfer accompanied by the decomposed gas flow through hydrate/ice solid matrix is reported focused on the comparison of spherical and cylindrical pellets having the same effective radius.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.268-275
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• 2008

The prediction of hydrate pellet decomposition characteristics is required to design the regasification process of GTS (gas to solid) technology, which is considered as an economic alternative for LNG technology to transport natural gas produced from small and stranded gas wells. Mathematical model based on the conservation principles, the phase equilibrium relation, equation of gas state and phase change kinetics was set up and numerical solution procedure employing volume averaged fixed grid formulation and extended enthalpy method are implemented. Initially, porous methane hydrate pellet is at uniform temperature and pressure within hydrate stable region. The pressure starts to decrease with a fixed rate down to the final pressure and is kept constant afterwards while the bounding surface of pellet is heated by convection. The predicted convective heat and mass transfer accompanied by the decomposed gas flow through hydrate/ice solid matrix is reported focused on the comparison of spherical and cylindrical pellets having the same effective radius.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.3
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• pp.267-281
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• 1994

The Combustion gas behavior induced by fire in a building is numerically investigated. The typical building for this analysis is partially divided by a vertical baffle projecting from the ceiling. The solution procedure includes the low Reynolds number ${\kappa}-{\varepsilon}$ model for the turbulent flow and the discrete ordinates method is used for the calculation of radiative heat transfer equation. The effects of the location and size of fire source and baffle length on velocity and temperature distributions, species mass fraction and flame location are analyzed. As the results of this study, it is found that the case when the fire source is located at the vertical wall is more dangerous than at the bottom wall in view of the combustion products and flame location. It is also found that the radiation effect cannot be neglected in analyzing the building in fire.

• Nuclear Engineering and Technology
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• v.29 no.4
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• pp.291-298
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• 1997

In advanced nuclear reactors, the passive containment cooling has been suggested to enhance the safety. The passive cooling has two mechanisms, air natural convection and oater cooling with evaporation. To confirm the coolability of PCCS, many works have been performed experimentally and numerically. In this study, the water cooling test was performed to obtain the evaporative heat transfer coefficients in a scaled don segment type PCCS facility which have same configuration with AP600 prototype containment. Air-steam mixture temperature and velocity, relative humidity and well heat flux are measured. The local steam mass flow rates through the vertical plate part of the facility are calculated from the measured data to obtain evaporative heat transfer coefficients. The measured evaporative heat transfer coefficients are compared with an analytical model which use a mass transfer coefficients. From the comparison, the predicted coefficients show good agreement with experimental data however, some discrepancies exist when the effect of wave motion is not considered. Finally, a new correlation on evaporative heat transfer coefficients are developed using the experimental values.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.5
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• pp.570-577
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• 2007

A micromachined convective accelerometer is a recently developed device. Typical micromachined accelerometers use a solid proof mass for measuring acceleration. But a micromachined convective accelerometer does not use a solid proof mass. A micromachined convective accelerometer is composed of a heating resistor and temperature sensors. This device measures acceleration by using convective heat transfer phenomenon. Therefore characteristics of a micromachined convective accelerometer are different as compared with typical micromachined accelerometer. In this research, we analyze the convective accelerometer by using transient convective heat transfer analysis. Based on the results of a convective accelerometer, we propose a new model which has improved performance.

• Journal of Energy Engineering
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• v.10 no.3
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• pp.266-271
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• 2001

Buoyancy-driven natural convection is analysed by employing a linear stability theory in hori-zontal porous media with net through flow. Darcy's law is used to model the flow characteristics in porous media. Bated on the results of linear stability analysis, a heat transfer correlation was obtained by employing weakly nonlinear analysis. As the net through flow increases, the system becomes more stable and the effect of the Darcy-Rayleigh number on the Nusselt number decreases.