• Nuclear Engineering and Technology
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• v.39 no.4
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• pp.299-312
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• 2007

The program on thermal-hydraulic evaluation by testing and analysis (THETA) for the development and licensing of the new design features in the APR1400 (Advanced Power Reactor-1400) is briefly introduced with a presentation on the research motivation and typical results of the separate effect tests and analyses of the major design features. The first part deals with multi-dimensional phenomena related to the safety analysis of the APR1400. One research area is related to the multidimensional behavior of the safety injection (SI) water in a reactor pressure vessel downcomer that uses a direct vessel injection type of SI system. The other area is associated with the condensation of steam jets and the resultant thermal mixing in a water pool; these phenomena are relevant to the depressurization of a reactor coolant system (RCS). The second part describes our efforts to develop new components for safety enhancements, such as a fluidic device as a passive SI flow controller and a sparger to depressurize the RCS. This work contributes to an understanding of the new thermal-hydraulic phenomena that are relevant to advanced reactor system designs; it also improves the prediction capabilities of analysis tools for multi-dimensional flow behavior, especially in complicated geometries.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05a
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• pp.304-309
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• 1997

A method to mitigate the thermal stratification flow of a horizontal pipe line is proposed by heating external bottom of the pipe with electrical heat tracing. Unsteady two dimensional model has been used to numerically investigate an effect of the external Denting to the thermally stratified flow. The dimensionless governing equations are solved by using the control volume formulation and SIMPLE algorithm. Temperature distribution, streamline profile and Nusselt numbers of fluids and pipe walls with time are analyzed in case of externally heating condition. no numerical result of this study shows that the maximum dimensionless temperature difference between the hot and the cold sections of pipe inner wall is 0.424 at dimensionless time 1,500 ann the thermal stratification phenomena is disappeared at about dimensionless time 9,000. This result means that external heat tracing can mitigate the thermal stratification phenomena by lessening $\Delta$ $T_{ma}$ about 0.1 and shortening the dimensionless time about 132 in comparison with no external heat tracing.rnal heat tracing.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.5
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• pp.365-375
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• 1991

Confined natural convection due to lateral temperature difference in rectangular enclosures was studied numerically and experimentally for the insulated and the constant temperature enclosures. In the case of insulated enclosure, the flow pattern and heat transfer modes are rather simple depending mainly upon Rayleigh number. In the case of isothermal enclosure, however, the phenomena of flow and heat transfer are somewhat complex and interesting due to the stable thermal gradients and various circumstances resulted from four wall temperature conditions. As a dimensionless variable, to describe properly the flow and heat transfer phenomena in the isothermal enclosure, temperature difference ratio ${\Delta}T_v/{\Delta}T_H$ is newly introduced and this parameter seems to be appropriate in the analysis of results on the effect of stabilizing thermal gradient.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.4
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• pp.153-160
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• 2001

In order to analyze the degradation process of epoxy/glass fiber for outdoor condition, FRP laminate was exposed to high temperature. Then, the degradation process was evaluated by comparing contact angle, surface potential, surface resistivity, and XPS. The experimental results showed that the amount of weight loss, contact angle, surface potential and surface resistivity increased up to 200 $^{\circ}C$ as a function of temperature. These phenomena show the existence of hydrophobic surface. With the change to the hydrophobic surface and the electrical potential and resistivity on FRP surface increased. In XPS to analyze surface chemical structures, the increased hydrophobicity in thermal increase of unsaturated double bond in carbon chains. Aslo, thermal treatment caused the discoloration on the point of treated surface. These phenomena were attributed to the generations of ether group.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.662-667
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• 2005

Nonlinear dynamics of active piezolaminated plates are investigated with respect to the thermopiezoelastic behaviors. For largely deformed structures with small strain, the incremental total Lagrangian formulation is presented based on the virtual work principles. A multi field layer wise finite shell element is proposed for assuring high accuracy and non-linearity of displacement, electric and thermal fields. For dynamic consideration of thermopiezoelastic snap through phenomena, the implicit Newmark's scheme with the Newton-Raphson iteration is implemented for the transient response of various piezolaminated models with symmetric or eccentric active layers. The bifurcate thermal buckling of symmetric structural models is first investigated and the characteristics of piezoelectric active responses are studied for finding snap through piezoelectric potentials and the load path tracking map. The thermoelastic stable and unstable postbuckling, thermopiezoelastic snap through phenomena with several attractors are proved using the nonlinear time responses for various initial conditions and damping loss factors. Present results show that thermopiezoelastic snap through phenomena can result in the difficulty of buckling and postbuckling control of intelligent structures.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1142-1145
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• 2004

ZnO surge arresters continuously endure the operating voltages during the operation course, and in the mean time, which need to withstand occasionally transient voltages of lightning and switching overvoltages. Under these voltages, the ZnO varistors inside arresters would have aging phenomena, one important result of aging phenomena is the increasing of resistive currents of varistors, which leads to the increasing of power losses of varistors. And the operating voltage is continuously applied on the ZnO varistors, there is a degradation phenomenon existing in ZnO varistors. When the degradation reaches a certain degree, then the arrester must stop operation. The degradation is related to the applied voltage ratio, the applied voltage ratio is high, the degradation is quickly. When the power loss is higher than the thermal dispersion ability of house of arrester, then the arrester will thermally breakdown. In this study the thermal stability characteristics of surge arresters for high power wil be discussed on the view point of watt losses and thermal breakdown.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.178-183
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• 2004

Thermal stratification phenomena in the liquid oxygen tank of launch vehicle is caused by heat influx from ambient and non-equilibrium heat and mass transfer in the cryogenic tank. The thermal stratification study is needed for designing vent system, tank insulation, pump inlet. In this paper by investigating buoyancy driven boundary layer flow by side wall heating, one dimensional analysis of thermal stratification is peformed. thermal gradient is described with time.

• Nuclear Engineering and Technology
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• v.39 no.4
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• pp.287-298
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• 2007

As part of the $AP1000^{TM}$ pressurized water reactor design certification program, a series of integral systems tests of the nuclear steam supply system was performed at the APEX-1000 test facility at Oregon State University. These tests provided data necessary to validate Westinghouse safety analysis computer codes for AP1000 applications. In addition, the tests provided the opportunity to investigate the thermal-hydraulic phenomena expected to be important in AP1000 small-break loss of coolant accidents (SBLOCAs). The APEX-1000 facility is a 1/4-scale pressure and 1/4-scale height simulation of the AP1000 nuclear steam supply system and passive safety features. A series of eleven tests was performed in the APEX-1000 facility as part of a U.S. Department of Energy contract. In all, four SBLOCA tests representing a spectrum of break sizes and locations were simulated along with tests to study specific phenomena of interest. The focus of this paper is the SBLOCA tests. The key thermal-hydraulic phenomena simulated in the APEX-1000 tests, and the performance and interactions of the passive safety-related systems that can be investigated through the APEX-1000 facility, are emphasized. The APEX-1000 tests demonstrate that the AP1000 passive safety-related systems successfully combine to provide a continuous removal of core decay heat and the reactor core remains covered with considerable margin for all small-break LOCA events.

• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.287-289
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• 2015

Meso-scale combustion is defined as combustion phenomena within limited characteristic length scales that are comparable with the laminar flame length scales. In the laminar flame theory, four representative length scales have been involved; i.e., a reaction layer thickness, a thermal layer thickness, a quenching distance, and a Markstein length. When the effects of these length scales on the flame characteristics are understood, the laminar flame theories can be clarified. Therefore, a study on the meso-scale combustion phenomena should not be thought as just a specific phenomena occurring in an exceptional combustion condition. Instead, all combustion phenomena within meso-scale spaces need to be explained by our knowledge. During this challenge, our understanding on laminar flame structures can be extended. Considering that most turbulent combustion phenomena in engineering application are still have local laminar flame structures, studies on laminar flame structures need to be re-visited especially in academic aspects.

• Journal of The Korean Astronomical Society
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• v.37 no.5
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• pp.493-500
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• 2004

The existence and extent of non-thermal phenomena in galaxy clusters is now well established. A key question in our understanding of these phenomena is the origin of the relativistic electrons which may be constrained by the modelling of the fine radio properties of radio halos and of their statistics. In this paper we argue that present data favour a scenario in which the emitting electrons in the intracluster medium (ICM) are reaccelerated in situ on their way out. An overview of turbulent-particle acceleration models is given focussing on recent time-dependent calculations which include a full coupling between particles and MHD waves.