• Membrane and Water Treatment
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• v.7 no.4
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• pp.297-311
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• 2016

Modeling and simulation of air humidification by hollow fiber membrane contactors are investigated in the current study. A computational fluid dynamic model was developed by solving the k-epsilon turbulence 2D Navier-Stokes equations as well as mass conservation equations for steady-state conditions in membrane contactors. Finite element method is used for the study of the air humidification under different operating conditions, with a focus on the humidity density, total mass transfer flux and velocity field. There has been good agreement between simulation results and experimental data obtained from literature. It is found that the enhancement of air stream decreases the outlet humidity from 0.392 to 0.340 (module 1) and from 0.467 to 0.337 (module 2). The results also indicated that there has been an increase in air velocity in the narrow space of shell side compared with air velocity wide space of shell side. Also, irregular arrangement has lower dead zones than regular arrangement which leads to higher water flux.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.2
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• pp.53-61
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• 2006

Axisymmetric numerical thermal analysis for a 3-dimensional regenerative cooling system in a rocket engine is carried out. To predict the accurate heat transfer with the stiff temperature distribution, several tests have been conducted for the grid size, the properties variation of the coolant and the combustion gas depending on temperature. The axisymmetric heat flux model is defined using fin efficiencies and is designed to be equivalent to the heat flux of the 3-dimensional coolant channel. For comparison purpose, the 1-dimensional analysis using Bartz equation is also conducted. The performance of the present model in predicting the cooling characteristics of a 3-dimensional regenerative cooling system is compared with the 3-dimensional results of RTE(Rocket Thermal Evaluation). It is found that the present method predicts much closer results to those of RTE code than 1-dimensional analysis.

• Journal of The Korean Astronomical Society
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• v.29 no.2
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• pp.93-105
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• 1996

We have solved the radiative transfer problem using a Sobolev approximation with an escape probability method in case of the supersonic expansion of a stellar envelope to an ambient medium. The radiation from the expanding envelope turns out to produce a P-Cygni type profile. In order to investigate the morphology of the theoretical P-Cygni type profile, we have treated $V_\infty,\;V_{sto},\;\beta$ (parameters for the velocity field), it and E(parameter for collisional effect) as model parameters. We have investigated that the velocity field and the mass loss rate affect the shapes of the P-Cygni type profiles most effectively. The secondarily important factors are $V_\infty,\;V_{sto}$. The collisional effect tends to make the total flux increased but not so much in magnitude. We have infered some physical parameters of 68 Cyg, HD24912, and $\xi$ persei such as $V_\infty,\;M$ from the model calculation, which shows a good agreenment with the observational results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.726-733
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• 1989

Conduction heat transfer in heat spreaders with concentrated heat sources is analyzed by finite element method calculation and the results are compared to analytical solutions for simplified cases. The local temperature rise is dependent on the heat flux, thermal conductivity of the spreader material, and the contact size of the heat source. The effect of the adjacency of other heat sources is also examined.

• Nuclear Engineering and Technology
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• v.42 no.5
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• pp.474-499
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• 2010

This paper presents the mostortant developments implemented in the APOLLO2 spectral code since its last general presentation at the 1999 M&C conference in Madrid. APOLLO2 has been provided with new capabilities in the domain of cross section self-shielding, including mixture effects and transfer matrix self-shielding, new or improved flux solvers (CPM for RZ geometry, heterogeneous cells for short MOC and the linear-surface scheme for long MOC), improved acceleration techniques ($DP_1$), that are also applied to thermal and external iterations, and a number of sophisticated modules and tools to help user calculations. The method of characteristics, which took over the collision probability method as the main flux solver of the code, allows for whole core two-dimensional heterogeneous calculations. A flux reconstruction technique leads to fast albeit accurate solutions used for industrial applications. The APOLLO2 code has been integrated (APOLLO2-A) within the $ARCADIA^{(R)}$ reactor code system of AREVA as cross section generator for PWR and BWR fuel assemblies. APOLLO2 is also extensively used by Electricite de France within its reactor calculation chain. A number of numerical examples are presented to illustrate APOLLO2 accuracy by comparison to Monte Carlo reference calculations. Results of the validation program are compared to the measured values on power plants and critical experiments.

• Journal of Environmental Science International
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• v.11 no.12
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• pp.1195-1204
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• 2002

We calculated dose rate using radiative transfer equations to consider radiative processes distinctly. The dose rate at Pohang(36°02'N, 129°23'E) was calculated using measured ozone and meteorological data and two-stream approximations(quadrature, Eddington, delta Eddington, PIFM(practical improved flux method), discrete ordinate, delta discrete ordinate) are used in solving equation. The purpose of this study is to determine the most compatible radiative transfer approximation for simulating the radiative and photochemical processes of atmosphere through comparision between calculated and measured values. Dose rate of the biologically effective irradiance in the region 0.28-0.32 U m showed the highest value when quadrature and Eddington was used and lower value on condition that delta scaling was applied. Correlation coefficient between dose rate at surface using radiation transfer equation and measured UV-B at Pohang was 0.78, 0.79 and 0.81 when delta Eddington, PIFM and delta discrete ordinate were used. Also, in case of above approximations were used, MBE(Mean Bias Error) was within -0.3MED/30min and RMBE(Relative Mean Bias Error) was below 10% between 1200 LST and 1400 LST Approximations which are compatible in estimating radiative process are delta Eddington, PIFM and delta discrete ordinate. Especially, in case that radiative process is considered more detail, delta discrete ordinate increased the number of stream is proper.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.18 no.1
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• pp.47-53
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• 1982

An analysis of convection, in a fully developed laminar steady flow through the vertical square duct under the condition of variational symmetric heat flux, is considered. Finite element solution algorithm by Galerkin's method with triangular elements and linear interpolation polynominals for the temperature and velocity profiles are derived for the vertical square duct. The comparison of temperature distribution due to variational symmetric heat flux in the duct were made with available the other data when the condition of peripheral heat flux were uniform and zero. Numerical values for the dimensionless temperatures and Nusselt numbers at selected Rayleigh numbers and pressure gradient parameters were obtained at a few nodal points for the vertical square ducts and effects of corner in the duct were investigated.

• KIEAE Journal
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• v.16 no.1
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• pp.81-87
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• 2016

Purpose: Heat transfers phenomena are described by the second order partial differential equation and its boundary conditions. In a three-dimensional structure of a building, the heat transfer phenomena generally include more than one material, and thus, become complicate. The analytic solutions are useful to understand heat transfer phenomena, but they can hardly be applied in engineering or design problems. Engineers and designers have generally been forced to use numerical methods providing reliable results. Finite volume methods with the unstructured grid system is only the suitable means of the analysis for the complex and arbitrary domains. Method: To obtain an numerical solution, a discretization method, which approximates the differential equations, and the interpolation methods for temperature and heat flux between two or more materials are required. The discretization methods are applied to small domains in space and time, and these numerical solutions form the descretized equations provide approximated solutions in both space and time. The accuracy of numerical solutions is dependent on the quality of discretizations and size of cells used. The higher accuracy, the higher numerical resources are required. The balance between the accuracy and difficulty of the numerical methods is critical for the success of the numerical analysis. A simple and easy interpolation methods among multiple materials are developed. The linear equations are solved with the BiCGSTAB being a effective matrix solver. Result: This study provides an overview of discretization methods, boundary interface, and matrix solver for the 3-dimensional numerical heat transfer including two materials.

• KIEAE Journal
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• v.16 no.6
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• pp.159-166
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• 2016

Purpose: The architectural structures in the engineering field include more than one material, and the heat transfer through these multiple materials becomes complicated. More or less, the analytic solutions obtained by the hand calculation can provide the limited information of heat transfer phenomena. However, the engineers have generally been forced to obtain reliable results than those of the hand calculation. The numerical calculation such as a finite volume methods with the unstructured grid system is only the suitable means of the analysis for the complex and arbitrary domains that consists of multiple materials. In this study, a new numerical code is developed to provide temperature distributions in the multiple material domains, and the results of this code are compared with the validation cases in ISO10211. Method: Finite volume methods with an unstructured grid is employed. In terms of numerical methods, the heat transfer conduction coefficient is not defined on the surface of the cell between different material cells. The heat transfer coefficient is properly defined to accurately mimic the heat transfer through the surface. The boundary conditions of heat flux considering radiation or heat convection are also developed. Result: The comparison between numerical results and ISO 10211 cases. We are confirmed that the numerical method provides the proper temperature distributions, and the heat transfer equation and its boundary conditions are developed properly.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.401-408
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• 2011

Nowadays, the development of sustainable transportation has been researched all over the world and Korea Railroad Research Institute (KRRI) is conducting a study in order to apply the sustainable Contactless Inductive Power Supply Technology to the electric railway system. But, inherent large flux leakage has limited the high power transmission because the gap of the Inductive Power Transformer(IPT) is much larger than one of the conventional transformers. In this study, a method to compensate the leakage flux and improve the power transmission by using LLC resonant inverter was proposed, incorporated in a built system, and verified by experimental work.