• Journal of the Korean Society for Precision Engineering
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• v.20 no.8
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• pp.175-184
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• 2003

A method of the shape design sensitivity analysis based on the boundary integral equation formulation is presented for two-dimensional inhomogeneous thermal conducting solids with multiple domains. Shape variation of the external and interface boundary is considered. A sensitivity formula of a general performance functional is derived by taking the material derivative to the boundary integral identity and by introducing an adjoint system. In numerical analysis, state variables of the primal and adjoint systems are solved by the boundary element method using quadratic elements. Two numerical examples of a compound cylinder and a thermal diffuser are taken to show implementation of the shape design sensitivity analysis. Accuracy of the present method is verified by comparing analyzed sensitivities with those by the finite difference. As application to the shape optimization, an optimal shape of the thermal diffuser is found by incorporating the sensitivity analysis algorithm in an optimization program.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.474-481
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• 2001

This paper addresses a numerical method for predicting transient temperature distributions in the wall of a curved pipe subjected to internally thermal stratification flow. A simple and convenient numerical method of treating the unsteady conjugate heat transfer in the non-orthogonal coordinate systems is presented. The proposed method is implemented in a finite volume thermal-hydraulic computer code based on a cell-centered, non-staggered grid arrangement, the SIMPLEC algorithm, a higher-order bounded convection scheme, and the modified version of momentum interpolation method. Calculations are performed for the transient evolution of thermal stratification in two curved pipes, where the one has thick wall and the other has so thin wall that its presence can be negligible in the heat transfer analysis. The predicted results show that the thermally stratified flow and transient conjugate heat transfer in a curved pipe with a finite wall thickness can be satisfactorily analyzed by the present numerical method, and that the neglect of wall thickness in the prediction of pipe wall temperature distributions can provide unacceptably distorted results.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2050-2054
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• 2007

This study numerically and experimentally investigated on thermal strain analysis of aluminum alloy casting mold using metal foundry. To predict the numerical result of thermal strain in Al alloy casting mold during the cooling process, it is performed the investigation of temperature distribution, stress and displacement based on the physical properties of Al alloy. In results of this study, Al alloy casting mold represented rapidly cooling graph during initial 20minutes after beginning cooling process, therefore value of stress and displacement is rapidly changed during initial 20minutes after beginning cooling process. In addition to, temperature distribution obtained by experiment confirmed corresponding pattern then compared numerical analysis with experiment. These results are distribute to make the effective and the high precision casting mold.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.11a
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• pp.283-288
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• 1996

Direct safety injection into the reactor vessel downcomer annulus(DVI) is a fundamental feature of the KNGR(Korean Next Generation Reactor) four-train safety injection system. The numerical analysis of thermal mixing of ECC(Emergency Core Cooling) water through DVI with the water in the RVDC(Reactor Vessel Downcomer) annulus has been performed, in order to study the impact of nozzle location on the pressurized thermal shock and safety analysis. The results of this study show that the thermal mixing due to the natural circulation induced by the limiting accident conditions is sufficient to prevent temperature in the RVDC from dropping to the level of concern for PTS. When the DVI nozzle is located right above the cold leg, the temperature distribution at the outlet of flow field is most uniform. The tool used for numerical analysis is CFDS-FLOW3D.

• Nuclear Engineering and Technology
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• v.32 no.2
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• pp.169-179
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• 2000

A detailed numerical analysis of the evolution of thermal stratification in a curved piping system in a nuclear power plant is performed. A finite volume based thermal-hydraulic computer code has been developed employing a body-fitted, non-orthogonal curvilinear coordinate for this purpose. The cell-centered, non-staggered grid arrangement is adopted and the resulting checkerboard pressure oscillation is prevented by the application of momentum interpolation method. The SIMPLE algorithm is employed for the pressure and velocity coupling, and the convection terms are approximated by a higher-order bounded scheme. The thermal-hydraulic computer code developed in the present study has been applied to the analysis of thermal stratification in a curved duct and some of the predicted results are compared with the available experimental data. It is shown that the predicted results agree fairly well with the experimental measurements and the transient formation of thermal stratification in a curved duct is also well predicted.

• 한국태양에너지학회:학술대회논문집
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• 2009.04a
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• pp.49-54
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• 2009

This study focus on verification of the thermal efficiency of volumetric receiver with $5kW_{th}$ Dish-type solar thermal system. Spiral flow path shaped on receiver and working fluid(steam) flow along the this flow path. Porous material for radiation-thermal conversion used in former researches are substituted with the stainless steel wall installed along the spiral shaped flow path. Numerical analysis for the flow path and temperature distributions are carried out. Numerical results are compared with experimental data. Using the numerical model, the heat transfer characteristics of spiral type receiver for dish-type solar thermal systems are known and the thermal performance of the receiver can be estimated.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.729-734
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• 2001

Thermal stratification due to turbulence penetration and in-leakage of valve cause the large thermal stress, which lead to fatigue crack of the piping system of nuclear power plant. So it is needed that numerical and experimental study for the phenomenon is conducted because there have not yet been sufficient study for the relationship between turbulence penetration and thermal stratification. Therefore numerical analysis is done here and respected to give a fundamental method of the approach to the phenomenon.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.5
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• pp.670-678
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• 1997

A method to mitigate the thermal stratification phenomenon of pressurizer surge line is proposed by heating bottom outside of horizontal pipe. Unsteady two dimensional model has been used to numerically investigate an effect of heating the bottom of pipe. The dimensionless governing equations are solved by using the control volume formulation and SIMPLE algorithm. Temperature and streamline profiles of fluids and pipe walls with time are compared with the previous study result. The numerical result of this study shows that the outside heating can relaxate the thermal stratification flow of the pressurizer surge line. Maximum dimensionless temperature difference between hot and cold sections of the pipe inner wall which causes thermal stratification was reduced from 0.514 to 0.424 at dimensionless time 1, 632 and 1, 500 respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.5
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• pp.401-409
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• 2013

Numerical analysis on RF (Radio-Frequency) thermal plasma treatment of micro-sized Ni metal was carried out to understand the synthesis mechanism of nano-sized Ni powder by RF thermal plasma. For this purpose, the behaviors of Ni metal particles injected into RF plasma torch were investigated according to their diameters ($1{\sim}100{\mu}m$), RF input power (6 ~ 12 kW) and the flow rates of carrier gases (2 and 5 slpm). From the numerical results, it is predicted firstly that the velocities of carrier gases need to be minimized because the strong injection of carrier gas can cool down the central column of RF thermal plasma significantly, which is used as a main path for RF thermal plasma treatment of micro-sized Ni metal. In addition, the residence time of the injected particles in the high temperature region of RF thermal plasma is found to be also reduced in proportion to the flow rate of the carrier gas In spite of these effects of carrier gas velocities, however, calculation results show that a Ni metal particle even with the diameter of $100{\mu}m$ can be completely evaporated at relatively low power level of 10 kW during its flight of RF thermal plasma torch (< 10 ms) due to the relatively low melting point and high thermal conductivity. Based on these observations, nano-sized Ni metal powders are expected to be produced efficiently by a simple treatment of micro-sized Ni metal using RF thermal plasmas.

• 한국신재생에너지학회:학술대회논문집
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• 2008.10a
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• pp.167-170
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• 2008

A numerical and experimental studies are carried out to investigate the transient heat transfer characteristics of 5kWth dish type solar air receiver. Measured solar radiation and temperatures at several different locations are used as boundary conditions for numerical simulation. Many parameters' effects (reflectivity of the reflector, the thermal conductivity of the receiver body, transmissivity of the quartz window, etc.) on the thermal performance are investigated. Discrete Transfer Method is used to calculate the radiation heat exchange in the receiver. A transient heat transfer model is developed and the rate of radiation, convection and conduction heat transfer are calculated. Comparing the experimental and numerical results, good agreement is obtained. Using the numerical model, the transient heat transfer characteristics of volumetric air receiver for dish type solar thermal systems are known and the transient thermal performance of the receiver can be estimated.