• Transactions on Electrical and Electronic Materials
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• 제13권2호
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• pp.51-59
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• 2012

Piezoelectric langasite crystals have superior properties such as high temperature performance and high quality Q and can be applied in combustion pressure sensors and surface acoustic wave (SAW) filters. Crystal growth, crystal structure and properties of langasite group are reviewed, and the mechanism of piezoelectricity of langasite is presented based on the crystal structure and deformation under high pressure. Finally, for the discovery of new piezoelectric materials, this paper presents the role of the framework, and recommends the search of framework crystal structure, because the characteristic of the mechanism exists on the framework of the crystal structure.

• 한국공작기계학회논문집
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• 제16권4호
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• pp.51-56
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• 2007

Precision positioning system with magnetostrictive actuator(MA) has widely used in manufacturing devices to control the positioning accuracy to meet the high load and stroke requirements. It has many advantage in comparison with piezoelectric actuator; high force, high strain, high efficient etc. But, the performance of Terfenol-D, the commercially available magnetostrictive material, is highly dependent on the prestress, magnetic field intensity and temperature. This paper present an experimental investigation of the temperature effect on displacement characteristics of magnetostrictive actuator. In this paper, compressed cold air is proposed to improve of positioning accuracy of magnetostrictive actuator. The compressed cold air cooling system has good cooling effect Experimental results confirming the effectiveness of the proposed cooling system as high precision positioning system are also has presented in this paper.

• Steel and Composite Structures
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• 제49권5호
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• pp.533-546
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• 2023

Cost-effective solutions provided by composite construction are gaining popularity which, in turn, promotes the appearance on the market of new types of composite sections that allow not only to take advantage of the synergy of steel and concrete working together at room temperature, but also to improve their behaviour at high temperatures. When combined with high performance materials, significant load-bearing capacities can be achieved even with reduced cross-sectional dimensions. Steel-reinforced concrete-filled steel tubular (SR-CFST) columns are one of these innovative composite sections, where an open steel profile is embedded into a CFST section. Besides the renowned benefits of these typologies at room temperature, the fire protection offered by the surrounding concrete to the inner steel profile, gives them an enhanced fire performance which delays its loss of mechanical capacity in a fire scenario. The experimental evidence on the fire behaviour of SR-CFST columns is still scarce, particularly when combined with high performance materials. However, it is being much needed for the development of specific design provisions that consider the use of the inner steel profile in CFST columns. In this work, a new experimental program on the thermo-mechanical behaviour of SR-CFST columns is presented to extend the available experimental database. Ten SR-CFST stub columns, with circular and square geometries, combining high strength steel and concrete were tested. It was seen that the circular specimens reached higher failure times than the square columns, with the failure time increasing both when high strength steel was used at the embedded steel profile and high strength concrete was used as infill. Finally, different proposals for the reduction coefficients of high performance materials were assessed in the prediction of the cross-sectional fire resistance of the SR-CFST columns.

• 동력기계공학회지
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• 제16권1호
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• pp.38-43
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• 2012

This paper describes an analysis on performance of R744-R404A cascade refrigeration system with internal heat exchanger to optimize the design for the operating parameters of the system. The operating parameters considered in this study include subcooling and superheating degree, internal heat exchanger and compression efficiency, evaporating and condensing temperature in the R744 low- and R404A high-temperature cycle and temperature difference of cascade heat exchanger. The main results are summarized as follows : COP of cascade refrigeration system increases with the increasing of compression efficiency, but decreases with the increasing temperature difference of cascade heat exchanger. Also, the COP increases with the increasing of internal heat exchanger efficiency in high-temperature cycle, but decreases with that in low-temperature cycle. Therefore, internal heat exchanger efficiency, compressor efficiency and temperature difference of cascade heat exchanger on R744-R404A cascade refrigeration system have an effect on the COP of this system.

• 한국수소및신에너지학회논문집
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• 제26권2호
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• pp.127-135
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• 2015

High-Temperautre Polymer Electrolyte Membrane Fuel Cell (HT-PEMFC) with phosphoric acid-doped polybenzimidazole (PBI) membrane has high power density because of high operating temperature from 100 to $200^{\circ}C$. In fuel cell stack, heat is generated by electrochemical reaction and high operating temperature makes a lot of heat. This heat is caouse of durability and performance decrease about stack. For these reasons, heat management is important in HT-PEMFC. So, we developed HT-PEMFC model and study heat flow in HT-PEMFC stack. In this study, we placed coolant plate number per cell number ratio as variable and analysed heat flow distribution in stack.

• 한국산업융합학회 논문집
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• 제18권1호
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• pp.37-44
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• 2015

In the research, we developed a device for cooling the drive section of the gripper of a robot for handling the high temperature material. In this study, By using a Peltier element, the high-temperature material is not affected and driving cylinder is cooled to prevent damage due to high temperatures. Hot part of the Peltier element is towards the robot gripper. Cool part of the Peltier element is towards the driving cylinder. The heat sink portion is made to keep the cooling effect. As the performance result, cooling-test is taken, and their result is satisfy.

• 한국연소학회지
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• 제16권1호
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• pp.46-51
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• 2011

Exhaust gas of an industrial furnace used at such as metallurgy or ceramic manufacturing usually contains thermal energy with high temperature which can be recycled by heat exchanger. However, when the temperature of the exhaust gas is high such as more than $1,000^{\circ}C$, ordinary metallic heat exchanger cannot fully recover the heat due to the limitation of operating temperature depending on the material property. In the present study, a compact ceramic heat exchanger of cross flow type is introduced and evaluated by heat exchange rate and operating temperature. The ceramic heat exchanger can endure the gas temperature more than $1,300^{\circ}C$, and its volumetric heat exchanging rate exceeds 1 MW/$m^3$. The experimental data is also compared with the previous numerical result which shows reasonable agreement. Meanwhile, the gas leakage rate is measured to be about 3~4%, and heat loss to environmental air is about 23~26% of the fuel energy.

• 마이크로전자및패키징학회지
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• 제23권3호
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• pp.7-14
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• 2016

High junction temperature directly or indirectly affects the optical performance and reliability of high power LEDs in many ways. This paper is focused on junction temperature characterization of LEDs. High power LEDs (3W) were tested in temperature steps to reach a thermal equilibrium condition between the chamber and the LEDs. The LEDs were generated by pulsed currents with duty ratios (0.091% and 0.061%) in multiple steps from 0mA and 700mA. The diode forward voltages corresponding to the short pulsed currents were monitored to correlate junction temperatures with the forward voltage responses for calibration measurement. In junction temperature measurement, forward voltage responses at different current levels were used to estimate junction temperatures. Finally junction temperatures in multiple steps of currents were estimated in effectively controlled conditions for designing the reliability of LEDs.

• Journal of Advanced Marine Engineering and Technology
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• 제32권5호
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• pp.670-676
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• 2008

A diesel engine requires a high Performance of lubrication because of the extreme conditions such as high temperature and pressure during combustion process in a cylinder. Many researches to improve the lubrication performance on the extreme condition have been executed. The lubricant oil suspended with nano-metal particles is the one of the measure. In this study, the nano-lubricant oil is applied on a commercial diesel engine, and the engine performance is tested. The results show the increase of maximum torque and the decrease of cylinder pressure, exhaust gas temperature, CO emission.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1090-1095
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• 2009

The purpose of this study is to determine the performance characteristics for the micro-channel gascooler with various operating conditions. The performance of four kind of HX models were analyzed and optimized with the variation of refrigerant inlet temperature, air velocity, outdoor temperature. As a result, Model B showed the maximum capacity and high performance could be maintained for wide operating conditions. Beside, the micro-channel heat exchanger could be appled to $CO_2$ system appropriately because of a small pressure drop and high heat transfer rate.