• Nuclear Engineering and Technology
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• v.35 no.3
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• pp.191-205
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• 2003

Effects of the width and location of a flow disturbing circular plate, installed at a vertical tube surface, on nucleate pool boiling heat transfer of water at atmospheric pressure have been investigated experimentally. Through the tests, changes in the degree of intensity of liquid agitation have been analyzed. The plate changes the fluid flow around the tube as well as heat transfer coefficients on the tube surface. It is identified that the plate width changes the rate of the circulating flow whereas its location changes the growth of the active agitating flow. Moreover, the flow chugging was observed at the downside of the plate.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.546-551
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• 1997

This paper presents a prediction of critical heat flux (CHF) in bubbly flow regime using dry-spot model proposed recently by authors for pool and flow boiling CHF and existing correlations for forced convective heat transfer coefficient, active site density and bubble departure diameter in nucleate boiling region. Without any empirical constants always present in earlier models, comparisons of the model predictions with experimental data for upward flow of water in vertical, uniformly-heated round tubes are performed and show a good agreement. The parametric trends of CHF have been explored with respect to variations in pressure, tube diameter and length, mass flux and inlet subcooling.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.46.3-47
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• 2016

We construct a solar eruption model with a background solar wind by performing three-dimensional zero-beta magnetohydrodynamic (MHD) simulation. The initial configuration of a magnetic field is given by nonlinear force-free field (NLFFF) reconstruction applied to a flux emergence simulation. The background solar wind is driven by upflows imposed at the top boundary. We analyzed the temporal development of the Lorentz force at the flux tube axis. Based on the results, we demonstrate that a solar eruption is caused by the imbalance between magnetic pressure gradient force and magnetic tension force. We conclude that this imbalance is produced by a weak but continuously existing solar wind above an active region.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.70.1-70.1
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• 2016

NGC 4402 is a spiral galaxy located in the Virgo cluster. It is undergoing active HI gas stripping due to the strong ICM pressure, showing evidence for recent quenching of star formation. Its CO disk is also highly disturbed as HI, yet unlike HI disk, no sign of significant molecular gas stripping is found. Aiming to better understand how atomic gas stripping and disturbed molecular gas result in star formation quenching, we probe properties of molecular gas in the densest forms. As a pilot study, we observed HCN (1-0) and HCO+ (1-0) in the center of NGC 4402 using one of the Korean VLBI Network (KVN) antennas located at Yonsei site. In this work, we present the result from the KVN single-dish observations and discuss its implications.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.69.3-70
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• 2016

We study the orbital histories of Virgo galaxies undergoing different HI gas stripping stages using phase-space diagrams. Based on the HI properties of galaxies, we find that location of galaxies is in good agreement with ram-pressure stripping predicted by numerical simulations with different infall time. For example, galaxies experiencing active gas stripping are mostly found in the first infall region showing high velocity with respect to the cluster center. Meanwhile, most galaxies that are likely to have lost gas a while ago are found in the cluster outskirts with low orbital velocities. We also discuss the cases where observational properties of galaxies and their locations in the phase-space do not well agree. In addition, we probe the phase-space of filaments and subgroups around or within Virgo. Our results strongly suggest that substructures can play important roles in galaxy evolution while galaxies are falling to the cluster.

• Journal of the Korea Institute of Military Science and Technology
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• v.3 no.2
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• pp.213-218
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• 2000

An experimental study was performed to investigate the effect of surface temperature mismatch on measurements of skin friction using a plug-type skin friction gage mounted on the side wall of a supersonic wind tunnel. The freestream Mach number was 2.4 and Reynolds number per meter was $5.25 {\times}10^7$ with total pressure of 50 psi and total temperature of 275K. Temperature mismatch between the gage surface and surrounding wall surface was generated by hot water injection using the active temperature control system. Results of the tests showed that the temperature mismatch made sizable effects on the measurements of skin friction.

• Geomechanics and Engineering
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• v.10 no.5
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• pp.565-575
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• 2016

Geosynthetics reinforced soil (GRS) walls constructed on weak grounds may change in both the horizontal earth pressure and deformation on wall facing. However, only few studies were done in the literature to measure and analyze the horizontal external deformation behavior of GRS walls constructed on soft grounds for a long period of time. The present study describes the external deformation behavior of GRS walls observed for 12-year long-term performance. The horizontal deformation of the geosynthetics-wrapped-facing GRS walls shows a passive behavior along one third of the wall height, from top going downwards, and active behavior for the rest of the wall height. Even if the geogrid and nonwoven geotextiles are exposed directly to sunlight and rainfalls in a span of 12 years, they have functioned well as wall facing. Therefore, the geosynthetic reinforcement material is strong enough to resist ultraviolet rays.

• Smart Structures and Systems
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• v.25 no.1
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• pp.105-109
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• 2020

The authors address the problem of ameliorating or updating existing educational buildings. This building typology is quite sensitive to social and media pressure, mainly when accidents have occurred nearby. When a building is classified as unsatisfactory, the current code requirements oblige one to re-design the building with significant penalty factors in the resistance values. Often the only solution is to destroy the existing facility and to build a new one. When attempting to preserve the existing building, higher levels of safety are demanded by the society and this can only be achieved by innovative system architectures. The authors propose and discuss a prototype that can be easily adopted to retrofit small educational buildings as the ones common in small municipalities. The higher performance is pursued by a special design of the control scheme, with new control devices and special control laws.

• Proceedings of the Safety Management and Science Conference
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• 1999.11a
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• pp.97-108
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• 1999

Most of chemical plant are using toxic and dangerous materials, inflammable and poisonous. There are many accidental dangers by escaping of fire, explosive and poisonous materials in case of high temperature and pressure. The accidents lead to taking employer's and local people's life and environmental contamination. Therefore, 27 small-medium chemical plant, which size is 30∼200 employees out of safety management agent in the area of A was selected in this study. The problems of safety management and several countermeasures at the chemical plants was indicated through the analyzed data. Prior to this analysis, top managers' concerns, equipment maintenance for the safety management are needed. For the future, calamity prevention countermeasures by industrial disaster analysis are needed and active safety management programs are investigated for the industrial disaster prevention and productivity enhancement at the chemical plant.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.3
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• pp.334-342
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• 1998

In this experimental study, methanol was chosen as a system material for a long -distance heat transportation. Not only transition metals but also noble metals were investigated as an active component, and several metal oxides, such as ${\gamma}$-$Al_2$,$O_3$, $SiO_2$, etc. as a support. In general, transition metal catalysts absorbed more heat than noble metal catalysts. The amount of heat absorption and CO selectivity depends on temperature and methanol partial pressure, and 25$0^{\circ}C$ Ni/$SiO_2$ catalyst showed the best result for methanol decomposition reaction.