• Proceedings of the Korean Nuclear Society Conference
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• 1999.05a
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• pp.107-107
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• 1999

Direct-contact condensation experiments of atmospheric steam and steam/air mixture on subcooled water flowing co-currently in a rectangular channel are carried out uszng an infrared thermal camera system to develop a temperature measurement method. The inframetrics Model 760 Infrared Thermal Imaging Radiometer is used for the measurement of the temperature field of the water film for various flow conditions. The local heat transfer coefficient is calculated using the bulk temperature gradient along the (low direction. It is also found that the temperature profiles can be used to understand the interfacial condensation heat transfer characteristics according to the flow conditions such as noncondensable gas effects, inclination effect, and flow rates.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2088-2093
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• 2008

In this study, flow field measurement of the Pebble Bed Reactor(PBR) for the High Temperature Gas-cooled Reactor(HTGR) was performed. Large number of pebbles in the core of PBR provides complicated flow channel. Due to the complicated geometries, numerical analysis has been intensively made rather than experimental observation. However, the justification of computational simulation by the experimental study is crucial to develop solid analysis of design method. In the present study, a wind tunnel installed with pebbles stacked was constructed and equipped with the Particle Image Velocimetry(PIV). We designed the system scaled up to realize the room temperature condition according to the similarity. The PIV observation gave us stagnation points, low speed region so that the suspected high temperature region can be identified. With the further supplementary experimental works, the present system may produce valuable data to justify the Computational Fluid Dynamics(CFD) simulation method.

• Nuclear Engineering and Technology
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• v.36 no.2
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• pp.165-174
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• 2004

The distributed resistance model has been recently implemented into the MATRA-LMR code in order to improve its prediction capability over the wire-wrap model for a flow blockage analysis in the LMR. The code capability has been investigated using experimental data observed in the FFM (Fuel Failure Mock-up)-2A and 5B for two typical flow conditions in a blocked channel. The predicted results by the MATRA-LMR with a distributed resistance model agreed well with the experimental data for wire-wrapped subchannels. However, it is suggested that the parameter n in the distributed resistance model needs to be calibrated accurately for a reasonable prediction of the temperature field under a low flow condition. Finally, the analyses of a blockage for the assembly of the KALIMER design are performed. Satisfactory results by the MATRA-LMR code were obtained through and rerified a comparison with results of the SABRE code.

• Bulletin of the Korean Chemical Society
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• v.16 no.7
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• pp.613-619
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• 1995

The influence of carrier solutions on particle retention was studied by varying surfactants and ionic strength in flow field-flow fractionation. Experiments were made with five different submicron polystyrene latex standards at three different types of surfactants and seven different ionic strengths. Departures in particle retention from the general theory were observed. At low ionic strength, it is shown that migrating sample zone is clearly lifted away from the ideal equilibrium height and that the repulsive interaction dominates between the particle and the channel wall. As ionic strength increases up to a certain level, particle retention becomes closer to the general theory. Further increase in ionic strength is shown to prolong the retention. An optimum regime of ionic strength is also suggested with the proper choice of surfactants.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.4
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• pp.561-575
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• 1996

The interaction of turbulent mixed convection and surface radiation in a three-dimensional channel with the heated blocks is analyzed numerically. Two blocks are maintained at high temperature and the other bottom and horizontal walls are insulated. S-4 method is employed to calculate the effect of the radiative heat transfer. The low Reynolds number k-$\varepsilon$ model proposed by Launder and Sharma is used to estimate the turbulent influence on the heat transfer enhancement. From above modeling, the effects of various channel specifications on the flow and heat transfer characteristics are investigated. The variables used for the present study are Reynolds number, block spacing, the channel height spacing for block and the emissivity. Average Nusselt numbers along the block surfaces are correlated and presented in terms of Reynolds number, emissivity and dimensionless geometric parameters. For the range of conditions in this study, average Nusselt numbers along the block surfaces are strongly influenced by the Reynolds numbers and channel height spacing for block but weakly influenced by the block spacing and the emissivity of the adiabatic walls.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2001.11a
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• pp.340-347
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• 2001

Security operating system applied to MAC(Mandatory Access Control) or to MLS(Multi Level Security) gives both subject and object both Security Level and value of Category, and it restrict access to object from subject. But it violates Security policy of system and could be a circulated course of illegal information. This is correctly IPC(Interprocess Communication)mechanism and Covert Channel. In this thesis, I tried to design and implementation as OS kernel in order not only to give confidence of information circulation in the Security system, but also to defend from Covert Channel by Storage and IPC mechanism used as a circulated course of illegal information. For removing a illegal information flow by IPC mechanism. I applied IPC mechanism to MLS Security policy, and I made Storage Covert Channel analyze system call Spec. and than distinguish Storage Covert Channel. By appling auditing and delaying, I dealt with making low bandwidth.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.48-55
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• 2017

Aeroacoustic computation of a fully-developed turbulent pipe flow at $Re_{\tau}=175$ and M = 0.1 is conducted by LES/LPCE hybrid method. The generation and propagation of acoustic waves are computed by solving the linearized perturbed compressible equations (LPCE), with acoustic source DP(x,t)/Dt attained by the incompressible large eddy simulation (LES). The computed acoustic power spectral density is closely compared with the wall shear-stress dipole source of a turbulent channel flow at $Re_{\tau}=175$. A constant decaying rate of the acoustic power spectrum, $f^{-8/5}$ is found to be related to the turbulent bursts of the correlated longitudinal structures such as hairpin vortex and their merged structures (or hairpin packets). The power spectra of the streamwise velocity fluctuations across the turbulent boundary layer indicate that the most intensive noise at ${\omega}^+$ < 0.1 is produced in the buffer layer with fluctuations of the longitudinal structures ($k_zR$ < 1.5).

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.1999-2010
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• 2023

Undesirable flapping motion of discs can cause the failure of swing check valves in nuclear passive safety systems. Time-resolved particle image velocimetry (PIV) was employed to investigate the flow characteristics around a free-to-rotate plate and the motion response, with the Reynolds numbers, based on the hydraulic diameter of the channel, from 1.32 × 10⁴ to 3.95 × 10⁴. Appreciable flapping motion (±3.52°) appeared at the Reynolds number of 2.6 × 10⁴ with the frequency of 5.08 Hz. In the low-Reynolds-number case, the plate showed negligible flapping. In the high-Reynolds-number case, the deflection angle increased with reduced flapping amplitude. The torque from the fluid determined the flapping amplitude. In the low-Reynolds-number case, Karman vortices were absent. With increasing Reynolds numbers, Karman vortices developed behind the plate with larger deflection angles. Strong interaction between the wake flow from the leading and trailing edge of the plate was observed. Based on power spectrum density (PSD) analysis, the vortex shedding frequency coincided with the flapping frequency, and the amplitude was positively correlated to the strength of the vortices. Proper orthogonal decomposition (POD) modes evince that, in the case of appreciable motion, coherent structures exhibited a larger spatial scale, enhancing the magnitude of the external torque on the plate.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2004.11a
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• pp.221-231
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• 2004

A kinetic theory analysis is made of low-speed gas flows in a microfluidic system consisted of three microchannels in series. The Boitzmann equation simplified by a collision model is solved by means of a finite difference approximation with the discrete ordinate method. For the evaluation of the present method results are compared with those from the DSMC method and an analytical solution of the Navier-Stokes equations with slip boundary conditions. Calculations are made for flows at various Knudsen numbers and pressure ratios across the channel. The results compared well with those from the DSMC method. It is shown that the analytical solution of the Navier-Stokes equations with slip boundary conditions which is suited fur fully developed flows can give relatively good results. In predicting the geometrically complex flows up to a Knudsen number of about 0.06. It is also shown that the present method can be used to analyze extremely low-speed flow fields for which the DSMC method is Impractical.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.43-46
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• 2007

To find out the optimum design of hydrogen storage and supply tank using Metal Hydride (briefly MH) and to make clear the performance characteristics under various conditions are our research purpose. In order to use the low-temperature exhaust heat, $LaNi_{4.7}Al_{0.3}$ which operates under the low pressure of 1MPa is chosen, and we measure the basic properties, namely density, specific heat, PCT(Pressure-Concentration-Temperature) characteristic, and effective thermal conductivity. Then, a numerical calculation model of hydrogen storage using MH alloy is suggested and this thermal diffusion equation of model is solved by the backward difference method. This calculation results rate compared with the experimental results of the systems which installed 1kg MH alloy and, it is found out that our calculation model can well predict the experimental results. By the experimental using MH alloy, it is recognized that the hydrogen flow rate can control by the step adjustment of brine temperature.