• Transactions of the Korean Society of Mechanical Engineers
• /
• v.7 no.4
• /
• pp.451-460
• /
• 1983

Computational four-equation turbulence model is developed and is applied to predict twodimensional unsteady thermal surface discharge into a reservoir. Turbulent stresses and heat fluxes in the momentum and energy equations are determined from transport equations for the turbulent kinetic energy (R), isotropic rate of kinetic energy dissipation (.epsilon.), mean square temperature variance (theta. over bar $^{2}$), and rate of destruction of the temperature variance (.epsilon. $_{\theta}$). Computational results by four-equation model are favorably compared with those obtained by an extended two-equation model. Added advantage of the four-equation model is that it yields quantitative information about the ratio between the velocity time scale and the thermal time scale and more detailed information about turbulent structure. Predicted time scale ratio is within experimental observations by others. Although the mean velocity and temperature fields are similarly predicted by both models, it is found that the four-equation model is preferably candidate for prediction of highly buoyant turbulent flows.

• Journal of Power System Engineering
• /
• v.2 no.3
• /
• pp.27-33
• /
• 1998

The room temperature and air conditioning load in the underground space have been investigated numerically by the unsteady heat conduction equation. The model room has 3 m in height and 10 m in width, and it's position in the underground depth are 0.5 m to 5 m. When the room was located around surface, the room temperatures were strongly influenced by the atmosphere. But the underground depth is more than 2 m, the yearly temperature amplitude was small and the temperature phase was delayed. Up to 5 m of the depth, the cooling and heating load was decreased rapidly, but over 10 m of the depth, the air conditioning load was constant.

• Journal of computational fluids engineering
• /
• v.10 no.4 s.31
• /
• pp.1-11
• /
• 2005

A numerical study of the evaluation of turbulence models for thermal striping phenomenon is performed. The turbulence models chosen in the present study are the two-layer model, the shear stress transport (SST) model and the V2-f model. These three models are applied to the analysis of the triple-jet flow with the same velocity but different temperatures. The unsteady Reynolds-averaged Navier-Stokes (URANS) equation method is used together with the SIMPLEC algorithm. The results of the present study show that the temporal oscillation of temperature is predicted by the SST and V2-f models, and the accuracy of the mean velocity, the turbulent shear stress and the mean temperature is a little dependent on the turbulence model used. In addition, it is shown that both the two-layer and SST models have nearly the same capability predicting the thermal striping, and the amplitude of the temperature fluctuation is predicted best by the V2-f model.

• Journal of the Korean Society of Safety
• /
• v.15 no.1
• /
• pp.59-65
• /
• 2000

The purpose of this study is to investigate the details of unsteady heat transfer in a heated fire door. This investigation is carried out numerically for two dimensional fire door which is composed of normal plasterboard and mild steel including air layer or heat shield. It is shown from the results that the recirculation occurs at the inner part of fire wall due to gravity force by temperature difference. The case I gives better adiabatic effect than the case II because temperature around the fire wall reachs at $230.96^{\circ}C$ in the case I and reachs at $450.37^{\circ}C$ in the case II.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.2
• /
• pp.680-688
• /
• 1996

In this paper, the unsteady state calculational model is proposed for the thermal stratification analysis in the feedwater line of the PWR plant. By defining dimensionless parameters in the two-dimensional polar coordinate system and applying SIMPLE algorithm, the temperature and flow profiles due to the thermal stratification are obtained. Base on the fact that the most significant condition occurs when the fluid temperature difference between the piping ends reaches as high as 166.deg. C, the present result shows that max. Dimensionless temperature difference of 0.6 (about l00.deg. C) obtained between hot and cold sections of pipe wall at dimensionless time 47.0.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.6 no.1
• /
• pp.1-11
• /
• 2002

The suitable turbulence model is found to be required in the course of establishing a proper analysis methodology for thermal stripping phenomena which are shown in strong temperature variation area such as reactors and propulsion devices. Three different turbulence models of $\kappa$-$\varepsilon$ model, modified $\kappa$-$\varepsilon$ model, and full Reynolds stress(FRS) model, are applied to analyze unsteady turbulent flows with temperature variation. Three test cases are selected for verification. These are vertical jet flows with water and sodium, and parallel jet flow with sodium. Analysis yields the conclusion that 3-D computation with FRS betters others. However, modified modeling is required to improve its heat transfer characteristic analysis. Further analysis is performed to find momentum variation effects on temperature distribution. It is found that the momentum increase results increase of fluid mixing and magnitude of temperature variation.

• Proceedings of the Korean Nuclear Society Conference
• /
• 2003.05a
• /
• pp.149.2-149.2
• /
• 2003

• Transactions of the Korean Society of Automotive Engineers
• /
• v.13 no.3
• /
• pp.123-130
• /
• 2005

In this study, we evaluated the CH4 and CO conversion efficiencies over the oxidation catalysts for natural gas vehicle with lean-burn system. On the fresh catalyst, the conversion efficiency was increased when the loading of precious metal was increased. On the aged catalyst, the conversion efficiency was decreased as increasing the excess air ratio. We could confirm the measuring conversion efficiency of the unsteady state with the FTIR and that of steady state with the GC The temperature increasing ratio of unsteady state is acceptable from 3$^{\circ}C$/min. to 15$^{\circ}C$/min. for the evaluation of catalyst conversion performance , which has within the 4$\%$ of the difference of conversion efficiency. We observed a physical behavior of the thermal aged catalyst's surface using TEM and BET device. It was found that the precious metal was grown to the micro-scopic size by thermal aging process.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.39 no.7
• /
• pp.634-642
• /
• 2011

A numerical analysis of steady/unsteady flow applying cavitation model and moving mesh method was carried out in order to analyze flow and response characteristics inside the pilot valve which controls the flight actuator system. The flow of the valve was assessed according to operation temperature and time. This research has found that valve characteristics became stable at above a specific temperature and the cavitation affected valve's performance. Internal pressure and response characteristics of the valve were analyzed and flow characteristics of steady and developed unsteady flow were confirmed to be matched each other.

• International Journal of Aeronautical and Space Sciences
• /
• v.3 no.1
• /
• pp.95-104
• /
• 2002

Numerical solution of the full Navier-Stokes equation as well as the energy equation has been obtained for the unsteady natural convection in a rectangular enclosure. One side wall was maintained at very high temperature simulating fires. Especially the effect of surface radiation was taken into account. While the enclosed air was assumed to be transparent, the internal walls directly interacted one another through the surface radiation. Due to a significant temperature difference in the flow field, the equation of state was used instead of the Boussinesq approximation. It was found that the rapid heating of the adiabatic ceiling and floor by the incoming radiation from the hot wall made the evolution at thermo-fluid field highly unstable in the initial period. Therefore, the secondary cells brought about at the floor region greatly affected the heat transfer mechanism inside the enclosure. The heat transfer rate was augmented by the radiation, resulting in requiring less time for the flow to reach the steady state. At the steady state neglecting radiation two internal hydraulic jumps were clearly observed in upper/left as well as in lower/right comer. However, the hydraulic jump in the lower/right comer could not be observed for the case including radiation due to its high momentum flow over the bottom wall. Radiation resulted in a faster establishment of the steady state phenomena.