• Tribology and Lubricants
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• v.40 no.3
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• pp.103-110
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• 2024

Gas foil thrust bearings (GFTBs) are oil-free self-acting hydrodynamic bearings that support axial loads with a low friction during airborne operation. They need solid lubricants to reduce dry-friction between the runner and top foil and minimize local wears on their surfaces during start-up and shutdown processes. In this study, we evaluate the lift-off speeds and load capacity performance of a GFTB with Polytetrafluoroethylene (PTFE) surface coating by measuring drag torques during a series of experimental tests at increasing ambient temperatures of 25, 75 and 110℃. An electric heat gun provides hot air to the test GFTB operating in the closed booth to increase the ambient temperature. Test results show that the increasing ambient temperature delays the lift-off speed and decreases the load capacity of the test GFTB. An early developed prediction tool well predicts the measured drag torques at 60 krpm. After all tests, post inspections of the surface coating of the top foil are conducted. Scanning electron microscope (SEM) images imply that abrasive wear and oxidation wear are dominant during the tests at 25℃ and 110℃, respectively. A quantitative energy dispersive spectroscopy (EDS) microanalysis reveals that the weight percentages of carbon, oxygen, and nitrogen decrease, while that of fluorine increases significantly during the highest-temperature tests. The study demonstrates that the increasing ambient temperature noticeably deteriorates the static performances and degrades the surface coating of the test GFTB.

• Journal of the Korean Electrochemical Society
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• v.10 no.3
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• pp.196-202
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• 2007

The performance characteristics of the polymer electrolyte fuel cells (PEFCS) were investigated under various humidification conditions at steady-state and transient conditions. The PEFC studied in this study was characterized by I-V curves in the potentiostatic mode and EIS (electrochemical impedance spectroscopy). The I-V curves representing steady-state performance were obtained from OCV to 0.25 V, and the dynamic performance responses were obtained at some voltages. The effects of anodic external humidification were measured by varying relative humidity of hydrogen from 20% to 100% while dry air was supplied in the cathode. At the high voltage region, the performance became higher with the increase of the temperature, while at the low voltage region, the performance decreased with the increase of temperature. The EIS showed that ohmic losses were larger at the dry condition of membrane and the effects of mass transport losses increased remarkably when the external and self-humidification were high. The dynamic responses were also monitored by changing the voltage of the PEFC instantly. As the temperature increased, the current reached steady-state earlier. The self-humidification with the generated water delayed the stabilization of the current except for low voltage conditions.

• Applied Chemistry for Engineering
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• v.32 no.1
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• pp.35-41
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• 2021

VWTi, which is used as a commercial catalyst in NH3-SCR, exhibits excellent denitrification performance at 300 to 400 ℃, but there is a problem that efficiency decreases at low temperatures below 300 ℃. Research on catalysts containing promoter to increase low-temperature denitrification efficiency is steadily progressing. However, research on the cause of the improvement in low-temperature denitrification efficiency of the catalyst and the catalyst properties is insufficient. In this study, it was confirmed that by adding Sb to VWTi, denitrification performance was improved by more than 10% in NH3-SCR reaction below 300 ℃. At this time, the space velocity and the size of the catalyst particles were controlled to exclude the influence of external/internal diffusion. In addition, the catalytic properties according to the presence or absence of Sb were investigated by performing BET, TEM/EDS, O2-TPD, H2-TPR and DRIFTs analysis. It was judged that the addition of Sb increased the adsorbed oxygen species on the surface of the catalyst, thereby enhancing the redox properties of the catalyst at low temperature and exhibiting excellent denitrification performance.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1811-1813
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• 2001

In order to obtain the useful data for quality control of the pole transformer and supply the stable electric power in distribution line, The evaluation of performance for low-loss pole transformer had been performed for new products and ones under operation for several years in distribution line. As the results, we found that the rate of fail were very high in gaskette, short-circuit strength and temperature-rise test, especially 48 percent in gaskette test.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.6
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• pp.738-747
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• 1999

Vector controlled induction motor have been widely used in high performance applications. How-ever the performance is sensitive to the variations of motor parameters especially the rotor time constant which varies with the temperature and the saturation of the magnetizing inductance. In this paper the authors propose new identifying method for time-varying parameters of an induction motor which is based on adaptive vector control with serial block algorithm. Vector con-trol system realized on synchronous frame and parameter identification system realized on sta-tionary frame are not easily affected by the vector control frame. Parameter mismatch in the control system results in heavy transient variation in speed and torque response. In order to compensate degradation of the responses at the middle and low speed region adaptive identifier is introduced. To verify the feasibility of this technique compute simu-lations carried out.

• Proceedings of the KWS Conference
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• 2006.05a
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• pp.71-73
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• 2006

Magnesium alloys are becoming important material for light weight car body, due to their low specific density but high specific strength. However they have a poor weldability, caused high oxidization tendency and low vapor temperature. In this study, the laser welding performance of magnesium alloys was investigated for automobile application. The materials were rolled magnesium alloy sheet contains 3%Al and 1%Zn. To evaluate the weldability, we examined the appearance of welding bead. The mechanical property was measured for welded specimen by tensile test. And formability was checked with the Erichsen tester. For the results, the performance of weld in laser welding was enough for press forming such as car body. But it was recommended to use filler wire for reduce the under fill.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.325-328
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• 2002

We developed a high performance 2.2" active matrix OLED display for IMT-2000 mobile phone. Scan and Data driver circuits were integrated on the glass substrate, using low temperature poly-Si(LTPS) TFT CMOS technology. High efficiency EL materials were employed to the panel for low power consumption. Peak luminescence of the panel was higher than 250cd/$m^2$ with power consumption of 200mW.

• Journal of Biosystems Engineering
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• v.22 no.2
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• pp.199-209
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• 1997

A one-pass rice whitener with hard metal blades was developed to solve the problems of the existing one-pass rice whitener. The developed one-pass rice whitener was tested and improved through various milling experiments. It showed high performance such as the capacity of 3.5 t/h, the energy consumption of $1.0 kWh/100kg$, milled rice recovery of 91.6%, broken rice rate of 2.2%, the crack rate of 1.9% at the 750 rpm of the roller shaft, compared with those other domestic and foreign one-pass rice whiteners. Especially, it could whiten broun rice of high moisture (16～l7%) with water sprayed at low internal pressure of less than $0.2 kg/cm^2$ and low temperature due to the characteristics of the cutting part composed of 24 hard metal blades. The developed one-pass rice whitener was industrilized and distributed to some rice processing complexs in one fourth price compared with that of imported one-pass rice whiteners.

• Journal of the Korean Ceramic Society
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• v.56 no.5
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• pp.435-442
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• 2019

Thermoelectric is a promising technology that can convert temperature differences to electricity (or vice versa). However, their relatively low efficiencies limit their applications to thermoelectric power generation systems. Therefore, low cost and high performance are important prerequisites for the application of thermoelectric materials to automotive thermoelectric generators. Silicide-based thermoelectric materials are good candidates for such applications. Recently, the thermoelectric performances of silicide-based thermoelectric materials have been significantly improved. However, increasing the thermoelectric performance of the materials while ensuring mechanical reliability remains a challenge. This review summarizes the preparation and design guidelines for silicide-based thermoelectric nanocomposites, as well as our recent progress in the development of nanocomposites with high thermoelectric performances or high mechanical reliabilities.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.11a
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• pp.143-146
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• 2002

A multilayer two-stage bandpass filter using dissimilar low-temperature cofired-ceramic (LTCC) materials is proposed in this paper. The proposed bandpass filter is composed of ceramic substrates with different dielectric constant instead of single ceramic material from top to bottom layer. Inductive elements are designed in a low permittivity ceramic layer to reduce parasitic effects and loss, while capacitive elements are designed in a high pertimitivity ceramic layer for size reduction. The center frequency of the proposed filter is 1.842 GHz, and the performance of the filter is analyzed and compared with the conventional LTCC filter with single material in terms of integration density, size reduction, and performance improvement.