• Architectural research
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• v.13 no.1
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• pp.25-32
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• 2011

The purpose of this research is to investigate the effect of specific hydration reaction on the stiffening process of cement paste. The cement compositions are manipulated to cause specific hydration reactions (secondary gypsum and syngenite formation) responsible for false set, and the relationship between specific hydration reactions and the flow and stiffening behavior of cement paste were investigated using modified ASTM C 403 penetration resistance measurement and oscillatory shear rheology. X-ray powder diffraction (XRD) was used for the phase identification associated with premature stiffening of cement paste. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were used for verification of syngenite formation. From the results, both secondary gypsum and syngenite formation caused faster stiffening and set. The amount of syngenite produced during 1 hour hydration was approximately 1 % of total mass of the cement paste, but cement paste with syngenite formation showed significantly accelerated stiffening behavior compared to normal cement paste.

• Proceedings of the KIEE Conference
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• 2001.10a
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• pp.200-204
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• 2001

A ZVZCS(Zero Voltage and Zero Current Switching) Three Level DC/DC Converter is presented to secondary auxiliary circuit. The new converter presented in this paper used a phase shift control with a flying capacitor in the primary side to achieve ZVS for the outer switch. A secondary auxiliary circuit, which consists of one small capacitor two small diode and one coupled inductor is added in the secondary to provides ZVZCS conditions to primary switches, ZVS for outer switches and ZCS for inner switches. Many advantages including simple circuit topology high efficiency, and low cost make the new converter attractive for high power applications. The principle of operation, feature and design considerations are illustrated and verified through the experiment with a 1kW 50kHz IGBT based experimental circuit.

• Nuclear Engineering and Technology
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• v.26 no.3
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• pp.345-354
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• 1994

Numerical Predictions including secondary flows have been Performed for fully developed turbulent single-phase rod bundle flows. The k-$\varepsilon$ turbulence model(two equation model) for the isotropic eddy viscosity, together with an algebraic stress model for generating secondary velocities, enabled the prediction of mean axial velocities, secondary velocities, and turbulent kinetic energy and turbulent stresses. Comparisons with experiment hate shown that the influence of secondary motion on mean flow and turbulence is dearly evident. The convective transport effects of secondary flow on the velocity field have been identified.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.2
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• pp.170-175
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• 2008

This paper describes the exact short-circuit current calculation technique for the single-phase transformer which is installed in the three-phase systems and shorted in the secondary side. Not only the results for a short-circuit current calculation in the existing literatures are wrong, but also little literature deals with the short-circuit current for a single-phase transformer. So, this paper presents a theoretical study and calculation method for a single-phase short current. The validity of the presented method is investigated through Simulation using "Power Tools" and "PSim" program.

• Proceedings of the KIEE Conference
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• 2005.04a
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• pp.149-151
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• 2005

This paper deals with the novel control algorithm of single-phase hybrid active power filter for the compensation of harmonic current components in nonlinear R-L load with passive active power filters. To construct two-axes coordinate, an imaginary second phase was made by giving time delay to line current. In this proposed method, the new signal, which was the delayed through the filtering by the phase-delay property of low-pass filter, is used as the secondary phase. Because two phases have different phase, instantaneous calculation of harmonic current is possible. In this paper, a reference voltage is created by multiplying gain of filter by compensation current using the rotating reference frames that synchronizes with source-frequency, not applying to instantaneous reactive power theory which has been used with the existing fixed reference frames. This paper shows the experimental results, which provide a high accuracy and extremely fast response of single-phase hybrid active Bower filter under the operation with the proposed control method.

• Journal of Welding and Joining
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• v.16 no.1
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• pp.114-124
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• 1998

The effect of matrix phase (austenite, pearlite, martensite) on the low stress abrasion resistance in the chromium-carbide-type high Cr white iorn hardfacing weld deposites has been investigated. In order to examine matrix phase, a series of alloys with different matrix phase by changing the ratio of Cr/C system by heat treatment were employed. The alloys were deposited twice on a mild steel plate using self-shielding flux cored arc welding process. The low stress abrasion resistance of the alloys against sands was measured by the Dry Sand/Rubber Wheel Abrasion Test(RWAT). Even though formation of pearlite phase in the matrix showed higher hardness than that of austenite, there was no observable difference in wear resistance between the pearlite and austenite phase for the same amount of chromium-carbide in the matrix. On the other hand, the formation of martensitic phase,, from heat treated austenitic alloys (high content of Cr), enhanced wear resistance due to its fine secondary precipitates.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.118-121
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• 2001

The investigation of cure kinetics and morphology studies on DGEBA/PEI/Anhydride system were performed by differential scanning calorimetry and scanning electron microscopy. Autocatalystic kinetics model was applied by isothermal scan test. Ozawa method and Kissinger method was applied by temperature scan. Activation energy was 95kJ/mol for neat DGEBA/NMA, 120kJ/mol for DGEBA/PEI(10p.h.r.)/NMA. The generation of secondary phase of PEI was observed and its size was grown up by increasing contents of PEI.

• 한국연소학회:학술대회논문집
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• 1999.10a
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• pp.139-148
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• 1999

In oder to analyze the effect of operating conditions on pulverized coal combustion, a numerical study is conducted at the pulverized coal combustor. Eulerian approach is used for the gas phase, whereas Lagrangian approach is used for the particle phase. Turbulence is modeled using standard ${\kappa}-{\varepsilon}$ model. The description of species transport and combustion chemistry is based on the mixture fraction/probability density function(PDF) approach. Radiation is modeled using P-l model. The turbulent dispersion of particles is modeled using discrete random walk model. Swirl number of secondary air affects the flame front, particle residence time and carbon conversion. Primary/Secondary air mass ratio also affects the flame front but little affects the carbon conversion and particle residence time. Air-fuel ratio only affects the flame front due to lack of oxygen. Radiation strongly affects the flame front and gas temperature distribution because pulverized coal flame of high temperature is considered.

• Proceedings of the KIPE Conference
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• 2010.11a
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• pp.30-31
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• 2010

Filament power supply (FPS) for neutral beam injection (NBI) consists of an insulation type is a device that heats the interior of Tokamak. The input/output specifications of FPS are 3-phase AC 200[Vpeak] and DC16V/300A respectively. A conventional FPS is composed of a 3-phase diode rectifier with DC-link, a H-bridge DC/DC converter, a high frequency transformer, a secondary rectifier and a LC-filter. In this paper, to improve the efficiency of PSFB DC/DC converter it is substituted IGBT devices instead of diode rectifier in secondary side. The proposed method is verified by computer simulation and experiment result.

• Journal of Ceramic Processing Research
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• v.13 no.spc1
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• pp.110-113
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• 2012

Ge-S and Li-Ge-S powders were synthesized via solution-based process in order to employ chalcogenide-based solid electrolyte for use in Li secondary batteries. GeCl4 and thioacetamide in combination result in Ge-S powders of which major crystalline phase becomes GeS2 where the tetragonal and orthorhombic phases coexist after heat treatment. A chemical treatment using NaOH brings about the reduction of chlorine in the powders obtained. However, the heat treatment at 300 ℃ is more effective in minimizing the chlorine content. When lithium chloride is used as the precursor of Li ions, the LiCl powders are agglomerated with an inhomogeneous distribution. When Li2S is used, the Li-Ge-S powders are distributed more uniformly and the orthorhombic GeS2 phase dominates in the powders.