• Journal of ILASS-Korea
• /
• v.17 no.2
• /
• pp.64-70
• /
• 2012

Water mist fire suppression systems which use relatively small droplets of water with high injection pressure are increasingly being used in wider applications because of its greater efficiency, low flooding damage and low toxicity. However, the performance of the system significantly relies on the water mist characteristics and it requires better understanding of fire suppression mechanism of water mist. In the present study, computational fluid dynamics simulations were carried out to investigate cooling performance of water mist in heated chamber. The gas phase was prepared with natural convection heat transfer model for incompressible ideal case and then the effects of water mist injection characteristics on cooling capabilities were investigated upon the basis of the pre-determined temperature field. For the simulation of water mist behavior, Lagrangian discrete phase model was employed by using a commercial code, FLUENT. Smaller droplet sizes, greater injection angles and higher flow rates provided relatively higher cooling performance.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.18 no.2
• /
• pp.178-183
• /
• 2013

The study of lightning surge have been conducted on information and communications equipment and power system. However, the research on SMPS itself is an inactive field. This paper analyzes surge current path of flyback converter with the combination wave generator by lightning surge. Also, this paper discloses that there exists the surge current with high-frequency component besides the low-frequency component based on the standard surge current. This high-frequency surge current is the major reason to damage the semiconductor devices such as FET and IC. To confirm the validity of the proposed issue, the analysis and experimental results are presented.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.08a
• /
• pp.327-327
• /
• 2011

A nonthermal bioplasma source was developed for application to human liquid fluids by making use of nano-size tungsten tips. Characteristics of the plasma source are investigated. Here we have used the AC voltage system. The bioplasma source generated by a tungsten tip with quartz tube and ground electrode is a low-temperature plasma without making any noticeable damage to cells at a low power operation. The breakdown voltage and current signals are measured by high voltage probe (Tektronix P6015A) and current probe (P6021). Variation of breakdown temperature near the tip electrode is larger than that in the neighborhood of ground electrode. Bubble formation during discharge has been recorded and investigated by using the high speed camera. The existence and behavior of hydroxyl and superoxide radicals are detected and measured by spectrometers. The electrical and optical properties of breakdown characteristics are also investigated.

• Nuclear Engineering and Technology
• /
• v.49 no.4
• /
• pp.781-786
• /
• 2017

The presence of crust on the inner walls of metallic ducts impairs transportation because crust completely or partially hinders the passage of fluid to the processing unit and causes damage to equipment connected to the production line. Its localization is crucial. With the development of the electronic imaging system installed at the Argonauta/Nuclear Engineering Institute (IEN)/National Nuclear Energy Commission (CNEN) reactor, it became possible to visualize crust in the interior of metallic piping of small diameter using real-time neutron radiography images obtained with a low neutron flux. The obtained images showed the resistance offered by crust on the passage of water inside the pipe. No discrepancy of the flow profile at the bottom of the pipe, before the crust region, was registered. However, after the passage of liquid through the pipe, images of the disturbances of the flow were clear and discrepancies in the flow profile were steep. This shows that this technique added the assembled apparatus was efficient for the visualization of the crust and of the two-phase flows.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.288-289
• /
• 2011

Indium Tin Oxide (ITO) is a typical highly Transparent Conductive Oxide (TCO) currently used as a transparent electrode material. Most widely used deposition method is the sputtering process for ITO film deposition because it has a high deposition rate, allows accurate control of the film thickness and easy deposition process and high electrical/optical properties. However, to apply high quality ITO thin film in a flexible microelectronic device using a plastic substrate, conventional DC magnetron sputtering (DMS) processed ITO thin film is not suitable because it needs a high temperature thermal annealing process to obtain high optical transmittance and low resistivity, while the generally plastic substrates has low glass transition temperatures. In the room temperature sputtering process, the electrical property degradation of ITO thin film is caused by negative oxygen ions effect. This high energy negative oxygen ions(about over 100eV) can be critical physical bombardment damages against the formation of the ITO thin film, and this damage does not recover in the room temperature process that does not offer thermal annealing. Hence new ITO deposition process that can provide the high electrical/optical properties of the ITO film at room temperature is needed. To solve these limitations we develop the Magnetic Field Shielded Sputtering (MFSS) system. The MFSS is based on DMS and it has the plasma limiter, which compose the permanent magnet array (Fig.1). During the ITO thin film deposition in the MFSS process, the electrons in the plasma are trapped by the magnetic field at the plasma limiters. The plasma limiter, which has a negative potential in the MFSS process, prevents to the damage by negative oxygen ions bombardment, and increases the heat(-) up effect by the Ar ions in the bulk plasma. Fig. 2. shows the electrical properties of the MFSS ITO thin film and DMS ITO thin film at room temperature. With the increase of the sputtering pressure, the resistivity of DMS ITO increases. On the other hand, the resistivity of the MFSS ITO slightly increases and becomes lower than that of the DMS ITO at all sputtering pressures. The lowest resistivity of the DMS ITO is $1.0{\times}10-3{\Omega}{\cdot}cm$ and that of the MFSS ITO is $4.5{\times}10-4{\Omega}{\cdot}cm$. This resistivity difference is caused by the carrier mobility. The carrier mobility of the MFSS ITO is 40 $cm^2/V{\cdot}s$, which is significantly higher than that of the DMS ITO (10 $cm^2/V{\cdot}s$). The low resistivity and high carrier mobility of the MFSS ITO are due to the magnetic field shielded effect. In addition, although not shown in this paper, the roughness of the MFSS ITO thin film is lower than that of the DMS ITO thin film, and TEM, XRD and XPS analysis of the MFSS ITO show the nano-crystalline structure. As a result, the MFSS process can effectively prevent to the high energy negative oxygen ions bombardment and supply activation energies by accelerating Ar ions in the plasma; therefore, high quality ITO can be deposited at room temperature.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.431-431
• /
• 2012

A compact tokamak reactor concept as a 14 MeV neutron source is desirable from an economic viewpoint for a fusion-driven transmutation reactor. LAR (Low Aspect Ratio) tokamak allows a potential of high "see full txt" operation with high bootstrap current fractions and can be used for a compact fusion neutron source. For the optimal design of a reactor, a radial build of reactor components has to be determined by considering the plasma physics and engineering constraints which inter-relate various reactor components and are constrained to use ITER physics and technology. In a transmutation reactor, the blanket should produce enough tritium for tritium self-sufficiency and the neutron multiplication factor, keff should be less than 0.95 to maintain sub-criticality. The shield should provide sufficient protection for the superconducting toroidal field (TF) coil against radiation damage and heating effects of the fusion neutrons, fission neutrons, and secondary gammas. In this work, characteristics of transmutation reactor based on LAR tokamak is investigated by using the coupled system analysis.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.18 no.8
• /
• pp.729-733
• /
• 2005

Al electrode for OLED was deposited by FTS (Facing Targets Sputtering) system which can deposit thin films with low substrate damage. The Al thin films were deposited on the cell (LiF/EML/HTL/Bottom electrode) as a function of working gas such as Ar or Ar+kr mixed gas. Also Al thin films were prepared with working gas pressure (1, 6 mTorr). The film thickness and I-V curve of Al/cell were measured and evaluated. In the results, when Al thin films were deposited using pure Ar gas, the turn-on voltage of Al/cell was about 11 V. And using the Ar:Kr($75\%:25\%$) mixed gas, the turn-on voltage of Al/cell decreased to about 7 V.

• Proceedings of the KSME Conference
• /
• 2001.06c
• /
• pp.322-326
• /
• 2001

Hard disk drive(HDD) consists of a head/slider system which flies over the magnetic disk at an extremely low height. As the density of HDD increases the flying height of the head needs to be decreased. This increases the chance for contact between the slider and the disk. This paper addresses some key issues related to surface failure characteristics of HDD. It is shown that flying behavior of the slider during contact-start-stop cycle can be analyzed based on different regimes of air film lubrication, experimental methods for identifying the underlying mechanisms and improving the reliability of HDD are discussed.

• Journal of Korea Technical Association of The Pulp and Paper Industry
• /
• v.33 no.2
• /
• pp.17-23
• /
• 2001

AKD sizing behavior of handsheets, which were prepared from the different pulps with various AKD fixing agents, was studied in this investigation. AKD sizing performance could be improved by removal of fines in the stock, minimizing damage of fiber, using a suitable fixing agent and heat treatment. Fillers with low surface energy, like calcium carbonate and talc, showed quite positive effect in AKD sizing. When PAM was added to the DIP stock as fixing agent, it showed lower sizing degree than polyamine did. But in case of NBKP system, PAM was more effective than polymine.

• Proceedings of the KIEE Conference
• /
• 2011.07a
• /
• pp.1212-1213
• /
• 2011

PWM(pulse width modulation) rectifier has unit power factor and low harmonic distortion with high power conversion efficiency in entire loading range. These merits of PWM rectifier help the spread of DC distribution system. In addition, if multiple PWM rectifiers can be operated in parallel connection, maintenance process can be simple and reliability of power source can be advanced because of the hot swapping is available. The other way, the load unbalance among rectifiers can force a converter to stop by over current. The surge current by closed circuit composition between rectifiers can force switching devices damage. In this paper, some problems that can occur in case of parallel operation of PWM rectifiers and problem eliminating methods are considered.