• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.129-136
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• 2010

This study is to investigate experimentally the engineering characteristics of cement mortar according to the replacement method and contents of recycled aggregate powder (RP) by collecting the recycled aggregate powder with the maximum size of below 0.08 mm and 0.15 mm. then, the results of the study can be summarized as follows. The flow of flesh mortar represented a trend in decreasing while the recycled aggregate powder was substituted as it is compared with that of plain. In addition, in case of correlation between tests, it appeared that the correlation between flow and ring flow is big. In the case of the characteristics of hardened mortar, the strength showed more improvements as the RP was substituted to aggregate than the case, which is substituted to aggregate. In addition, it was verified that the results in which the RP was substituted to aggregate by 5% represented similar values to that of the plain according to the passage of age.

• Journal of the Korean Institute of Gas
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• v.11 no.1 s.34
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• pp.23-28
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• 2007

This paper presents an experimental investigation on the sealing defects and cracks of O-rings and a valve packing of a gas valve for a LPG cylinder. O-ring in which stops a gas leakage of a liquefied petroleum gas is very important for a LPG valve safety. Valve packing is to open and close a gas flow port for supplying and charging a LPG fuel. The sealing performance of two sealing units ism related to the leak safety and long lift of a gas valve. The investigated results show that most of O-rings was failed due to a circumferential crack in which is caused by partial press bonding failure near the partition zone and an excess compression rate. Some of the O-ring failure was originated by an extrusion of an excessive leak pressure of a LP gas. Thus, this paper strongly recommends a tight quality control and a safety guarantee system of O-rings and valve packing to guarantee a leak safety and to extend a service lift of a gas valve. At the end, a warranty policy of the sealing units should be adopted for increasing a product quality and safety of a gas valve.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.6
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• pp.655-662
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• 2014

This study conducted tensile tests on an Alloy 690TT tube at room temperature (RT) and at $343^{\circ}C$ using tube- and ring-type specimens to investigate the stress-strain behavior and tensile properties of a steam generator (SG) tube in the axial and circumferential directions at RT and at the design temperature of a nuclear power plant (NPP). The results of the axial tensile test showed that yield point phenomena appeared at both RT and $343^{\circ}C$, and serrated flow in the stress-strain curve appeared at $343^{\circ}C$. Yield and tensile strengths for both directions were clearly lower at $343^{\circ}C$ compared to RT; however, the elongations were approximately the same at both test temperatures. Regardless of the test temperature, the strengths in the circumferential direction were lower by approximately 5~10 % than those in the axial direction. In addition, the test data revealed that the reduction in the yield and tensile strengths of the Alloy 690TT SG tube with the test temperature was more significant than that estimated by the temperature correction factor of ASME Sec.II.

• Bulletin of the Korean Chemical Society
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• v.9 no.6
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• pp.338-341
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• 1988

Two crystal structures of fully dehydrated silver and potassium exchanged zeolite A, stoichiometries of $Ag_{9.3}K_{{2.7}^-}A$ (${\alpha}$ = 12.282(2) ${\AA}$) and $Ag_{10.7}K_{{1.3}^-}{\AA}$ (${\alpha}$ = 12.287(2) A) per unit cell, have been determined from 3-dimensional x-ray diffraction data gathered by counter methods. All structures were solved and refined in the cubic space group Pm3m at 21(1)$^{\circ}C$ . The crystals of $Ag_{9.3}K_{{2.7}^-}A$ and $Ag_{10.7}K_{{1.3}^-}A$ were prepared by flow method using exchange solutions in which mole ratios of $AgNO_3$ and $KNO_3$ were 1:10 and 1:5, respectively, with total concentration of 0.05M. The structures of the dehydrated $Ag_{9.3}K_{{2.7}^-}A$ and $Ag_{10.7}K_{{1.3}^-}A$ were refined to yield the final error indices $R_1$ = 0.037 and $R_2$ = 0.040 with 321 reflections, and $R_1$ = 0.042 and $R_2$ = 0.043 with 371 reflections, repectively, for which I > 3${\sigma}$(I). In both structures, eight $Ag^+$ ions are found nearly at 6-ring centers and each $Ag^+$ ion is nearly in the (1 1 1) plane at its O(3) ligands. The 8-ring sites are preferentially occupied by $K^+$ ions in both structures. 1.3 and 1.7 reduced silver atoms per unit cell were found inside of sodalite units of $Ag_{9.3}K_{{2.7}^-}A$ and that of $Ag_{10.7}K_{{1.3}^-}A$, respectively. These reduced silver species were presumably formed from the reduction of $Ag^+$ ions by oxide ions of residual water molecule or of the zeolite framework. These two crystals may be presented as hexasilver cluster in 21.7% and 28.3% of sodalite unit cells for $Ag_{9.3}K_{{2.7}^-}A$ and $Ag_{10.7}K_{{1.3}^-}A$, repectively.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.5
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• pp.551-556
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• 2007

High pressure storage of the agent gas in fire suppression system was composed of tank, main valve and safety valve, which prevents the fracture of the high pressure storage. The safety valve has circular thin plate as fracture plate that was destroyed over fracture pressure. When inner pressure of the storage is reached the fracture pressure, the safety valve discharges gas and degrades simultaneously the inner pressure of the storage. There are design variables such as flow path diameter, inner diameter of the plastic packing ring, thickness of plate and fillet radius. In this variables, thickness of plate is set to be a value of 0.2mm. The main effect of variables on the inner pressure, has been decided using factorial design and statistical analysis. Therefore, the relation of variables are expressed by regression equation. It is disclosed results that the difference of fracture pressures between the equation and experiment has $2{\sim}5%$. Finally, using response surface method, the optimal design of the safety valve could be decided with safety pressure of 25MPa, where the fracture occurs on circular thin plate.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.8
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• pp.891-898
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• 2005

Inertia welding is a solid-state welding process in which butt welds in materials are made in bar and in ring form at the joint race, and energy required lot welding is obtained from a rotating flywheel. The stored energy is converted to frictional heat at the interface under axial load. The quality of the welded joint depends on many parameters, including axial force, initial revolution speed and energy amount of upset. working time, and residual stresses in the joint. Inertia welding was conducted to make the large exhaust valve spindle for low speed marine diesel engine. superalloy Nimonic 80A for valve head of 540mm and high alloy SNCrW for valve stem of 115mm. Due to different material characteristics such as, thermal conductivity and flow stress. on the two sides of the weld interface, modeling is crucial in determining the optimal weld geometry and Parameters. FE simulation was performed by the commercial code DEFORM-2D. A good agreement between the Predicted and actual welded shape is observed. It is expected that modeling will significantly reduce the number of experimental trials needed to determine the weld parameters. especially for welds for which are very expensive materials or large shaft. Many kinds of tests, including macro and microstructure observation, chemical composition tensile , hardness and fatigue test , are conducted to evaluate the qualify of welded joints. Based on the results of the tests it can be concluded that the inertia welding joints of the superalloy exhaust valve spindle are better properties than the material specification of SNCrW.

• Proceedings of the Korean Vacuum Society Conference
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• 1996.06a
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• pp.40-41
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• 1996

Nitridation technique has been receiving much attention for the formation of a thin nitrided buffer layer on which high quality nitride films can be formedl. Particularly, gallium nitride (GaN) has been considered as a promising material for blue-and ultraviolet-emitting devices. It can also be used for in situ formed and stable passivation layers for selective growth of $GaAs_2$. In this work, formation of a thin nitrided layer is investigated. Nitrogen electron cyclotron resonance(ECR)-plasma is employed for the formation of thin nitrided layer. The plasma source used in this work is a compact ECR plasma gun3 which is specifically designed to enhance control, and to provide in-situ monitoring of plasma parameters during plasma-assisted processing. Microwave power of 100-200 W was used to excite the plasma which was emitted from an orifice of 25 rnm in diameter. The substrate were positioned 15 em away from the orifice of plasma source. Prior to nitridation is performed, the surface of n-type (001)GaAs was exposed to hydrogen plasma for 20 min at $300{\;}^{\circ}C$ in order to eliminate a native oxide formed on GaAs surface. Change from ring to streak in RHEED pattern can be obtained through the irradiation of hydrogen plasma, indicating a clean surface. Nitridation was carried out for 5-40 min at $RT-600{\;}^{\circ}C$ in a ECR plasma-assisted molecular beam epitaxy system. Typical chamber pressure was $7.5{\times}lO^{-4}$ Torr during the nitridations at $N_2$ flow rate of 10 seem.(omitted)mitted)

• Journal of the Economic Geographical Society of Korea
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• v.21 no.2
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• pp.107-118
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• 2018

Due to the rapid economic development, traffic congestion has become a dire concern in Beijing, China. Levying a congestion toll is seen as the most effective solution to the problem. Building a congestion pricing model is a crucial step in implementing a workable toll scheme. Unlike previous attempts, this study not only covers the theoretical discussion but also considers three practical issues: the speed-density relationship, the value of travel time savings, and the determination of optimal traffic volume. We estimate the speed-density relationship by regression models and the value of travel time saved through survey results. We further suggest a way through which the government could identify the optimal traffic flow by a series of trial-and-errors, without the knowledge of exact road demand structure. Finally, a practical tolling scheme is proposed for Beijing's second ring road along with some policy recommendations.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.332-332
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• 2010

We have successfully demonstrated the inkjet printing method to create $Al_2O_3$ films withouWe have successfully demonstrated the inkjet printing method to create $Al_2O_3$ films without a high temperature sintering process. In order to remove the coffee ring effect in the ink drop, we have introduced a co-solvent system in order to create Marangoni flow in the ink drop, which leads to the dense packing of ceramic powders on the substrate during inkjet process. The packing density of the Inkjet-printed $Al_2O_3$ films is around 60% (max. 70%) which is very high compared to the value obtained from the same material films by other conventional methods such as film casting, dip coating process, etc. The voids inside the films (which are around 40% of the entire film volume) are filled with the polymer resin (Cyanate ester) by the infiltration process. This resin infiltration is also implemented by the inkjet printing process right after the Ah03 film ink-jetting process. The microstructures of the printed $Al_2O_3$ films are investigated by Scanning Electron Microscope (SEM) to understand the degree of packing density in the printed films. The inkjet-printed $Al_2O_3$ films have been characterized to investigate its thickness and roughness. Quality factor of the printed $Al_2O_3$ film is also measured to be over 300 at 1MHz.

• Aerospace Engineering and Technology
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• v.3 no.2
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• pp.81-90
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• 2004

This paper describes the results of combustion performance test of fuel-rich gas generator(GG) using LOx and kerosene as propellant at off-design conditions. The chamber pressure is thought to be a function of O/F ratio and total propellant mass flow rate. The test shows that the spatial temperature deviation at the exit of gas generator remains within 7.5K and that the average gas temperature at the exit is a function of propellant O/F ratio. The results of firing test of gas generator at off-design conditions, especially the relation between gas temperature and O/F ratio, can provide useful data for the design of future gas generator and for the development of low-O/F ratio reaction analysis code.