• 한국안전학회지
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• 제14권1호
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• pp.19-24
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• 1999

A two dimensional thermo elasto-plastic finite clement stress analysis was performed to study stress distributions in functionally gradient material. The upper $ZrO_2$ surface is heated at 1200K until a steady state is established and cooled at 300K. The influences on the thermal stress distributions due to the difference of compositional gradient exponent p were investigated. In this study, we obtained the thermal stresses are low for p=1.

• 한국결정성장학회지
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• 제13권1호
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• pp.1-4
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• 2003

In the present work we consider morphological structure of the faces of BGO crystals grown by Czochralski technique under the conditions of low temperature gradient (0.1~1 deg/cm) and interconnection between the morphological features of faces at the crystallization front and the formation of defects within the crystal volume. It is demonstrated that the {112} faces retain stability while the growing surface deviates from the crystallographic (112) plane up to 1 degree. At larger deviation, the region of the stable facet growth passes either to the region of macrosteps or to the region of normal growth. depending on conditions.

• 한국초전도ㆍ저온공학회논문지
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• 제23권3호
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• pp.14-19
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• 2021

The reduction of carbon dioxide emissions becomes a global issue, the main source of carbon dioxide emissions in the Asian region is the energy conversion sector, especially coal-fired power plants. We are working to develop technologies that will at least limit the increase in carbon dioxide emissions from the thermal power plants as one way to reduce carbon dioxide emissions. Our research aims to reduce carbon dioxide emissions by removing iron oxide scale from the feedwater system of thermal power plants using a superconducting high-gradient magnetic separation (HGMS) system, thereby reducing the loss of power generation efficiency. In this paper, the background of thermal power plants in Asia is outlined, followed by a case study of the introduction of a chemical cleaning line at an actual thermal power plant in Japan, and the possibility of introducing it into the thermal power plants in China based on the results.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제34회 추계학술대회 개최
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• pp.27-34
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• 2001

A new functionally gradient metal coating method using an atomic mixing technique was developed. In this work the effect of silver atomic mixing on the tribological characteristics of silver$.$ films. has been investigated experimentally. Atomic mixing was implemented by using the, bombardment .of accelerated Ar ions during the thermal evaporation coating process of silver films. Experiments were performed in dry conditions using a ball-on-disk test rig at a load range of 19.6 mN - 17.64 N and a sliding velocity of 20 mm/sec. Results showed that the life of functionally gradient silver coating was enhanced about 100 times more than that of thermally evaporated silver coating and 2 times more than that of IBAD silver coating. The functionally gradient. film also showed low friction and wear compared to those of the evaporated silver and

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 추계 학술대회논문집
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• pp.221-225
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• 2004

Evaluation of turbulence models is performed for a better prediction of thermal stratification in an upper plenum of a liquid metal reactor by applying them to the experiment conducted at JNC. The turbulence models tested in the present study are the two-layer model, the $\kappa-\omega$ model, the v2-f model and the low-Reynolds number differential stress-flux model. When the algebraic flux model or differential flux model are used for treating the turbulent heat flux, there exist little differences between turbulence models in predicting the temporal variation of temperature. However, the v2-f model and the low-Reynolds number differential stress-flux model better predict the steep gradient o( temperature at the interface of thermal stratification, and only the v2-f model predicts properly the oscillation of temperature. The LES Is needed for a better prediction of the amplitude and frequency of the temperature fluctuation.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.866-870
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• 2008

In this study, we designed cold gas propulsion system with minimum 0.25 mm nozzle and micro-thrust measurement system to analyze flow characteristic of micro propulsion system in ambient and vacuum condition. Argon and Nitrogen are used for propellant and the result of experiments is compared with CFD analysis and theory. But there is a point where reduced scale versions of conventional propulsion systems will no longer be practical. Therefore, a fundamentally different approach to propulsion systems was taken. That is thermal transpiration based micro propulsion system. It has no moving parts such as lubricants, pressurizing system and can pump the gaseous propellant by temperature gradient only(cold to hot). We are advancing basic research of propulsion system based on thermal transpiration in vacuum conditions and had tried experiment process and theoretical access in advance. To characterize membrane of Knudsen pump, we select Polyimide material that has low thermal conductivity(0.29 W/mK) and can stand high temperature($300^{\circ}C$) for long time. And we fabricated hole diameter 1, 0.5, 0.2, 0.1 mm using precision manufacturing. Experimental results show that pressure gradient efficiency of Knudsen pump is increased to maximum 82% according to Knudsen number and thick membranes are more effective than thin membranes in transition flow regime.

• Advances in nano research
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• 제16권6호
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• pp.579-591
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• 2024

This study explained the effects of radiation, magnetic field, and nanoparticle shape on the peristaltic flow of an Upper-Convected Maxwell nanofluid through a porous medium in an asymmetric channel for a better understanding of cooling and heating mechanisms in the presence of magnetic fields. These phenomena are modeled mathematically as a system of non-linear differential equations, that are solved under long-wavelength approximation and low Reynolds number conditions using the perturbation method. The results for nanofluid and temperature described the behavior of the pumping characteristics during their interaction with (the vertical position, thermal radiation, the shape of the nanoparticle, and the magnetic field) analytically and explained graphically. Also, the combined effects of thermal radiation parameters and some physical parameters on pressure rise, pressure gradient, velocity, and heat distribution are pointed out. Qualitatively, a reverse velocity appears with combined high radiation and Grashof number or combined high radiation and low volume flow rate. At high radiation, the spherical nanoparticle shape has the greatest effect on heat distribution.

• 한국전기전자재료학회논문지
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• 제16권9호
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• pp.842-850
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• 2003

The suspension insulators are subjected to harsh environments in service for a long time. The long-term reliability of tile insulators is required for both mechanical and electrical performances. This study describes some basic performance tests and accelerated aging test by cool-heat cycling methods and thermal mechanical performance test methods on alumina porcelain insulators (new and aged) used for transmission line in KOREA. There was no fail in electrical and mechanical performance tests such as a high voltage strength, a flashover voltage, and an impact strength in all samples. But in the case of accelerating aging tests which have above 9$0^{\circ}C$ temperature gradient, fracture phenomena was happened by a thermal shock in tile aged sample(sample A) with low alumina porcelain body. It was indicated that sample A was more severely aged than other samples. According to results of HRB test and microstructural analysis, it was reasoned that insulator bodies with the matrix reinforced with alumina crystalline phase have advantages over the suppression of crack advance. And cool-heat aging and mechanical thermal ageing tests shows that a temperature gradient is more effective to accelerating than a cycling number.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2005년도 춘계학술대회
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• pp.674-677
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• 2005

The characteristics of geothermal resources in Korea was roughly estimated using hot springs, 580 geothermal gradients and 338 heat flow data. In the aspect of hot springs with geologic structure, location of hot springs coincide with fault zone, especially younger age of Cretaceous to Tertiary. In the aspect of geothermal gradients, Pohang area shows the highest geothermal gradient anomaly, which is covered with unconsol idated rock of low thermal conductivity preserving the residual heat from igneous activity or radioactivity elements decay. In the aspect of heat flow density, high anomaly can be found along the zone connecting Uljin-Pohang-Busan on the southeastern part of Korean peninsula at which big fault zone as Yangsan fault is well developed.

• 한국표면공학회지
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• 제57권3호
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• pp.155-164
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• 2024

Physical properties of carbon nanomaterials are dependent on their nanostructures and they are modified by diverse synthesis methods. Among them, thermal plasma method stands out for synthesizing carbon nanomaterials by controlling chemical and physical reactions through various design and operating conditions such as plasma torch type, plasma gas composition, power capacity, raw material injection rate, quenching rate, kinds of precursors, and so on. The method enables the production of carbon nanomaterials with various nanostructures and characteristics. The high-energy integration at high-temperature region thermal plasma to the precursor is possible to completely vaporize precursors, and the vaporized materials are rapidly condensed to the nanomaterials due to the rapid quenching rate by sharp temperature gradient. The synthesized nanomaterials are averagely in several nanometers to 100 nm scale. Especially, the thermal plasma was validated to synthesize low-dimensional carbon nanomaterials, carbon nanotubes and graphene, which hold immense promise for future applications.