• Proceedings of the KIEE Conference
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• 2004.11a
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• pp.220-222
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• 2004

The piezoelectric ceramics for a step-up piezoelectric transformer are desired large electromechanical coupling factor, high mechanical quality factor and good characteristic resonance frequency. In this study, the empirical formula of specimens is used $0.9Pb(Zr_xTi_{1-x})O_3-0.1Pb(Mn_{1/3}Nb_{1/3}Sb_{1/3})O_3$ (PZT-PMNS). The piezoelectric and dielectric characteristic are investigated by sintering temperature and value of x as functions of $Ti^{2+}$, $Zi^{2+}$ mol rate. MPB(morphotropic phase boundary) is defined in the x=0.522. Because it is appeared to the best piezoelectric and dielectric characteristic in the x=0.522, it can be application of step-up transformer.

• Journal of Power System Engineering
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• v.18 no.6
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• pp.200-206
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• 2014

This paper deals with deterministic PI controller design based on dynamic characteristics for refrigeration system. The temperature control system of an oil cooler is described as a typical 2nd order model of the refrigeration system which has zeros in a transfer function. PI controller gains satisfying control specifications are represented by the dynamic characteristic functions using relationship between the parameters and the control specifications in the model. Phase margin was considered to increase robustness of the oil cooler control system. Furthermore, the influence of zeros in the model to the control specifications was analyzed in detail for improving control performance. The validity of the suggested PI controller design was investigated using the four types of gains which had been already confirmed their control performances through experiments.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.64 no.4
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• pp.256-260
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• 2015

In this paper, achieved rise temperature distribution about degradation phenomenon of 24 MVA distribution cast resin transformer using CFD(Computational Fluid Dynamics). Usually, life of transformer is depended on temperature distribution of specification region than thermal special quality of transformer interior. Specially, life of transformer by decline of dielectric strength decreases rapidly in case rise by strangeness transformer interior hot spot temperature value permits. Because calculating high-voltage(HV) winding and low-voltage(LV) winding of cast resin transformer and Joule's loss of core for improvement these life, forecasted heat source, and HV winding and LV winding of cast transformer rise temperature distribution of core for supply of electric power and temperature distribution of highest point on the basis of the results. Also, calculated temperature rise limit of cast resin transformer and permission maximum temperature using analysis by electromagnetic heat source. Calculated and forecasted rise temperature distribution by heat source of thermal analysis with calculated result.

• Journal of the Korean Ceramic Society
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• v.45 no.3
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• pp.185-189
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• 2008

In order to fabricate porous ceramics, hydrated sodium silicate was synthesized by hydrothermal reaction using anhydrous sodium silicate. The microstructural and the structural characteristics of the expanded ceramics were observed depending on heat treatment temperature (550, 600, 650, $700^{\circ}C$) and then the effect of these characteristics on the compressive strength and the temperature gradient was investigated. As the heat treatment temperature was increased, the compressive strength was decreased from $0.717KN/cm^2\;(550^{\circ}C)\;to\;0.166KN/cm^2\;(700^{\circ}C)$. The temperature gradient was increased with increasing the experimental temperature regardless of the heat treatment temperature. The temperature gradient of the expanded ceramics which was heat treated at $650^{\circ}C\;was\;300^{\circ}C$. The bulk specific gravity, porosity, pore size, pore characteristics and wall thickness were varied depending on heat treatment temperature, and the compressive strength and the temperature gradient were governed by the complex effects of these factors.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.3
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• pp.218-223
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• 2012

This study is focused on the evaluation of thermal output of TABS (Thermally Activated Building System). The aim of this study is to evaluate TABS in terms of the temperature difference between heating medium supply temperature ($T_s$) and return temperature ($T_r$), thermal output and the surface temperature distribution according to the design flow rate and the design flow temperature. Through the transient heat transfer simulation using temperature calculation using Crank-Nicolson FDM using Physibel Voltra 6.0 W, the temperature difference between $T_s$ and ��$T_r$, thermal output and the surface temperature distribution of specific TABS was calculated and evaluated. The results show that specific thermal output and temperature difference at $60^{\circ}C$ of supply water temperature were about 162 $W/m^2$, $13.6^{\circ}C$ respectively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.2
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• pp.205-214
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• 1999

The objective of this paper is to investigate the thermal properties of TMA clathrate compound applicable to cold storage system for building air-conditioning. Especially, the test tube experiments are performed by comparing and analyzing the temperature of phase change, specific heat and subcooling characteristic according to the variation of density, temperature of heat source and charging quantity in TMA clathrate compound. The results are summarized as follows:1) $-15^{\circ}C$ is not proper as the temperature of heat source because the temperature of subcooling is above $8.3^{\circ}C$ 2) temperature of phase change is dropped as the temperature of heat source is lower, 3) the effect of subcooling suppression with about 8$^{\circ}C$ is confirmed when the temperature of heat source is $-10^{\circ}C$ in case of 26, 27, and 30wt%, while the temperature of subcooling is about $0^{\circ}C$ when the temperature of heat source is $-15^{\circ}C$ in case of 25, 26 and 30wt%. Thus, the effect of subcooling suppression is greater as the temperature of heat source is lower. Additionally, the concentrative study is needed on mass concentration causing the phase change without subcooling phenomenon when the temperature of heat source is $-15^{\circ}C$. Thus, it is concluded that TMA clathrate compound has enough thermal properties as the cold storage medium for building air-conditioning.

• Geomechanics and Engineering
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• v.24 no.2
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• pp.157-166
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• 2021

This paper aims at the temperature and slenderness ratio effects on physical and mechanical properties of Beishan granite. A series of uniaxial compression tests with various slenderness ratios and temperatures were carried out, and the acoustic emission signal was also collected. As the temperature increases, the fracture aperture of intercrystalline cracks gradually increases, and obvious transcrystalline cracks occurs when T > 600℃. The failure patterns change from tensile failure mode to ductile failure mode with the increasing temperature. The elastic modulus decreases with the temperature and increases with slenderness ratio, then tends to be a constant value when T = 1000℃. However, the peak strain has the opposite evolution as the elastic modulus under the effects of temperature and slenderness ratio. The uniaxial compression strength (UCS) changes a little for the low-temperature specimens of T < 400℃, but a significant decrease happens when T = 400℃ and 800℃ due to phase transitions of mineral. The evolution denotes that the critical brittle-ductile transition temperature increases with slenderness ratio, and the critical slenderness ratio corresponding to the characteristic mechanical behavior tends to be smaller with the increasing temperature. Additionally, the AE quantity also increases with temperature in an exponential function.

• Tribology and Lubricants
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• v.19 no.1
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• pp.21-25
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• 2003

The 440C stainless steel is used for ball bearings and bevel gears in the control rod drive mechanism for the integral reactor, SMART. The friction characteristics of 400C stainless steel a investigated in sliding motion using the reciprocating tribometer which can simulate the operating conditions of the control rod drive mechanism. Highly purified water is used as lubricant, and the water is heated and pressurized in the autoclave. Friction force on the reciprocating specimens is measured by the load cells and transformed into friction coefficient. It is verified that frictional characteristic of the 440c steel is not drastically changed up to operating temperature and variation of friction coeffcient at operating temperature from room temperature to 160$^{\circ}C$ is within 5%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.228-229
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• 2009

$VO_2$ thermistor was fabricated on $Al_2O_3$ substrate. and has a CTR (Critical Temperature Resistor) characteristic. $VO_2$ thermistor has a about $10^6$ resistance($\Omega$) in normal temperature. But When temperature is a about $80^{\circ}C$, Resistance of $VO_2$ thermistor is a about some hundred resistance: The resistance of $VO_2$ thermistor increased with increasing length and decreasing width.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.04b
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• pp.88-91
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• 2000

The $(Sr_{0.85}Ca_{0.15})TiO_3$(SCT) thin films are deposited on Pt-coated electrode(Pt/TiN/$SiO_2$/Si) using RF sputtering method. The crystallinity of SCT thin films is increased with increase of substrate temperature in the temperature range of 200~500$[^{\circ}C]$. V-I characteristics of SCT thin films show the increasing leakage current with the increases of deposition temperature. The conduction mechanism of the SCT thin films observed in the temperature range of 25~100$[^{\circ}C]$ can be divided into four characteristic regions with different mechanism by the increasing current.