• Journal of the Korean Society of Safety
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• v.34 no.4
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• pp.1-5
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• 2019

In the field of combined cycle power generation, thermal barrier coating(TBC) protects the super-heat-resistant alloy, which forms the core component of the gas turbine, from high temperature exposure. As the turbine inlet temperature(TIT) increases, TBC is more important and durability performance is also important when considering maintenance cost and safety. Therefore, studies have been made on the fabrication method of TBC and super-heat-resistant alloy in order to improve the performance of the TBC. In recent years, due to excellent properties such as high temperature creep resistance and high temperature strength, turbine blade material have been replaced by a single crystal superalloy, however there is a lack of research on TBC applied to single crystal superalloy. In this study, to understand the isothermal degradation performance of the TBC applied to the single crystal superalloy, isothermal exposure test was conducted at various temperature to derive the delamination life. The growth curve of thermally grown oxide(TGO) layer was predicted to evaluate the isothermal degradation performance. Also, microstructural analysis was performed by scanning electron microscope(SEM) and energy dispersive X-ray spectroscopy (EDS) to determine the effect of mixed oxide formation on the delamination life.

• Journal of Power Electronics
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• v.15 no.3
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• pp.841-848
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• 2015

As a vital part of renewable energy and electrical traction, power converters are supposed to have high reliability and good performance. However, power semiconductors produce considerable heat when the power converter works, which results in high junction temperatures that lower the reliability and performance of the power semiconductors. Many studies show that ambient humidity has a significant effect on power devices, but the influence of high humidity on junction temperatures has yet to be studied. Therefore, this paper presents a thermal model for power converters in moist air to obtain the junction temperature increase, which is utilized for the power converter used in a Switched Reluctance Motor System. Simulation results show that the law of converter temperature distribution is independent of the relative humidity in the case of fixed ambient temperature, whereas the temperature in the power converter decreases as the ambient relative humidity increases. These simulation results are validated with the experimental results.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.9
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• pp.447-454
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• 2017

In this study, local velocity distribution of cooling air in a heat exchanger used in an air compressor for a railway car was measured and heat transfer characteristics of the heat exchanger were analyzed. First, heat transfer coefficient and fin performance of the cooling air side were predicted and was checked if the fin of the heat exchanger was effectively used. Distribution of air flow rate at high temperature side was predicted through pipe network analysis and heat resistance at high temperature and low temperature side were predicted and compared. Spatial distribution of temperature in the interior and surface of the square channel constituting high-temperature side was predicted and appropriateness of the size of the heat exchanger was examined. As a result of the analysis, the present size of the heat exchanger could be reduced and it could be effective to promote heat transfer inside the heat exchanger rather than outside to improve performance of the heat exchanger.

• Nuclear Engineering and Technology
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• v.54 no.12
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• pp.4412-4421
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• 2022

The pressure measurement in the high-temperature liquid metal system, such as Sodium-cooled Fast Reactor(SFR), is important and yet it is very challenging due to its nature. The measuring pressure is relatively at low range and the applied temperature varies in wide range. Moreover, the pressure transfer material in impulse line needs to considered the high temperature condition. The conventional diaphragm-based approach cannot be used for it is impossible to remove the effect of thermal expansion. In this paper, the Fiber Bragg Grating(FBG) sensor-based pressure measuring concept is suggested that it is free of problems induced by the thermal expansion. To verify this concept, a prototype was fabricated and tested in an appropriate conditions. The uncertainty analysis result of the experiment is also included. The final result of this study clearly showed that the FBG-based pressure transmitter system is applicable to the extreme environment, such as SFR and any other high-temperature liquid metal system and the measurement uncertainty is within reasonable range.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.1
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• pp.70-75
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• 2013

It has fabricated membrane electrode assemblies (MEA) for proton exchange membrane fuel cell by hot-pressing method. The hot-pressing was used for the fabrication of MEA which is composed of commercial platinum electrode on carbon paper. The performance of MEA was studied with different fabrication conditions of temperature, pressure and torque. As the temperature increased, the performance of MEA was increased. and started to decrease l after arrived at the maximum performance of MEA. This is related with good contact between electrode and polymer electrolyte membrane at high temperature and microstructural change at much higher temperature. Similarly, as the pressure increased, the performance of the MEA increased up to highest values and start to decrease. According to the our results, the maximal performance of the MEA was at the temperature of $140^{\circ}C$ and the pressure of $1.5{\times}10^3$ kPa. The optimal torque to assemble the single stack was 3.2 N m.

• Korea-Australia Rheology Journal
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• v.21 no.2
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• pp.91-102
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• 2009

This paper describes an extension of viscoelastic Group Interaction Modelling (GIM) to predict the relaxation response of linear, branched and cross-linked structures. This model is incorporated into a Monte Carlo percolation grid simulation used to generate the topological structure during the isothermal cure of a gel, so enabling the chemorheological response to be predicted at any point during the cure. The model results are compared to experimental data for an epoxy-amine systems and good agreement is observed. The viscoelastic model predicts the same exponent power-law behaviour of the loss and storage moduli as a function of frequency and predicts the cross-over in the loss tangent at the percolation condition for gelation. The model also predicts the peak in the loss tangent which occurs when the glass transition temperature surpasses the isothermal cure temperature and the system vitrifies.

• Journal of the Korean Ceramic Society
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• v.48 no.4
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• pp.328-333
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• 2011

The influence of Al-doped ZnO (AZO) thin films degraded under high temperature and damp heat on the performance deterioration of Cu(In,Ga)$Se_2$ (CIGS) solar cells was investigated. CIGS solar cells with AZO/CdS/CIGS/Mo structure were prepared on glass substrate and exposed to high temperature ($85^{\circ}C$) and damp heat ($85^{\circ}C$/85% RH) for 1000 h. As-prepared CIGS solar cells had 64.91% in fill factor (FF) and 12.04% in conversion efficiency. After exposed to high temperature, CIGS solar cell had 59.14% in FF and 9.78% in efficiency, while after exposed to damp heat, it had 54.00% in FF and 8.78% in efficiency. AZO thin films in the deteriorated CIGS solar cells showed increases in resistivity up to 3.1 times and 4.4 times compared to their initial resistivity after 1000 h of high temperature and damp heat exposure, respectively. These results can be explained by the decreases in carrier concentration and mobility due to diffusion or adsorption of oxygen and moisture in AZO thin films. It can be inferred that decreases in FF and conversion efficiency were caused by an increase in series resistance, which resulted from an increase in resistivity of AZO thin films degraded under high temperature and damp heat.

• Journal of the Korean Ceramic Society
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• v.53 no.6
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• pp.689-699
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• 2016

The effects of composition, structure design, and coating thickness of thermal barrier coating (TBC) on thermal barrier performance were investigated by measuring the temperature differences of TBC samples. TBCs with the thin and thick top coats were used for these studies, including TBCs with rare-earth (Gd, Yb, and La) compositions. The thermal barrier performance was enhanced with increasing the thickness of top coat even for thin TBCs, indicating that the thermal barrier performance was commensurate to the thickness of top coat. On the other hand, the bi-layered TBC, which was prepared with Yb-Gd-YSZ feedstock powder, with the buffer layer of high purity 8YSZ showed a better thermal barrier performance than that of regular purity 8YSZ. The interfaces in the bi-layered TBCs had a decisive effect on the thermal barrier performance, showing the performance enhanced with increasing numbers of interfaces. However, a new structural design and an additional process should be considered to reduce stress concentrations and to ensure interface stability, respectively, for improving thermal durability in the multi-layered TBCs.

• Journal of the Microelectronics and Packaging Society
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• v.9 no.3
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• pp.43-48
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• 2002

In this study, high performance electrode catalyst was developed in fabrication of membrane electrode assembly for PEMFCs(Polymer Electrolyte Membrane Fuel Cells). The I-V characteristics were measured to evaluate the influence of Nafion solution and Pt loading amount in the catalyst composition. The electrode characteristics were also investigated with respect to temperature change. The electrode performance was optimized at Nafion 5 wt% and 0.5 mg Pt/$\textrm{cm}^2$ content. The increase in the concentration of Nafion solution resulted in the decrease in electrode performance. At $80^{\circ}C$ of unit cell, I-V characteristics excelled those obtained at lower temperature. There was no difference in performance at low current density, but the improvement of voltage value in higher temperature could be found at high current density.

• Tribology and Lubricants
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• v.31 no.4
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• pp.141-147
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• 2015

Gas foil thrust bearings (GFTBs) have attractive advantages over rolling element bearings and oil film thrust bearings, such as oil-free operation, high speed stability, and high-temperature operation. However, GFTBs have lower load carrying capacity than the other two types of bearings owing to the inherent low gas viscosity. The load carrying capacity of GFTBs depends mainly on the compliance of the foil structure and the formed hydrodynamic wedge, where the gas pressure field is generated between the top foil and the thrust runner. The load carrying capacity of the GFTBs is very important for the suitable design of oil-free turbomachinery with high performance. The aim of the present study is to identify the characteristics of the load carrying performance of GFTBs. A new test rig for the experimental measurements is designed to provide static loads up to 800 N using a pneumatic cylinder. The maximum operating speed of the driving motor is 30,000 rpm. A series of experimental tests—lift-off test, static load performance test, and maximum load capacity test—estimate the performance of a six-pad GFTB, in terms of the static load, driving torque, and temperature. The maximum load capacity is determined by increasing the static load until the driving torque rises suddenly with a sharp peak. The test results show that the torque and temperature increase linearly with the static load. The estimated maximum load capacity per unit area is approximately 80.5 kPa at a rotor speed of 25,000 rpm. The test results can be used as a design guideline for GFTBs for realizing oil-free turbomachinery.