• 한국분말재료학회지
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• 제15권5호
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• pp.345-351
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• 2008

The effects of the dopant (Mn) ratio on the microstructure and thermoelectric properties of $FeSi_2$ alloy were studied in this research. The alloy was fabricated by a combination process of ball milling and high pressure pressing. Structural behavior of the sintered bulks were systematically investigated by XRD, SEM, and optical microscopy. With increasing dopan (Mn) ratio, the density and ${\varepsilon}-FeSi$ phase of the sintered bulks increased and maximum density of 94% was obtained in the 0.07% Mn-doped alloy. The sintered bulks showed fine microstructure of ${\alpha}-Fe_{2}Si_{5}$, ${\varepsilon}-FeSi$ and ${\beta}-FeSi_2$ phase. The semiconducting phase of ${\beta}-FeSi_2$ was transformed from ${\alpha}-Fe_{2}Si_{5}+{\varepsilon}-FeSi$ phase by annealing.

• 대한기계학회논문집B
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• 제31권5호
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• pp.467-472
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• 2007

In this study the penetration distance of liquid phase fuel(i.e. liquid phsae length) was investigated in evaporative field. An exciplex fluorescence method was applied to the evaporative fuel spray to measure and investigate both the liquid and the vapor phase of the injected spray. For accurate investigation, images of the liquid and vapor phase regions were recorded using a 35mm still camera and CCD camera, respectively. Liquid fuel was injected from a single-hole nozzle (l/d=1.0mm/0.2mm) into a constant-volume chamber under high pressure and temperature in order to visualize the spray phenomena. Experimental results indicate that the liquid phase length decreased down to a certain constant value in accordance with increase in the ambient gas density and temperature. The constant value, about 40mm in this study the, is reached when the ambient density and temperature of the used fuel exceed critical condition.

• Journal of Mechanical Science and Technology
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• 제15권12호
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• pp.1860-1868
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• 2001

An experimental investigation was carried out to clarify unsteady flow fields with rotating stall cell, especially behavior of stall cell, in a high specific-speed diagonal flow fan. As its specific-speed is vary high for a diagonal flow fan, its pressure-flow rate curve tends to indicate unstable characteristics caused by rotating stall similar to axial flow fan. Although for an axial flow fan many researchers have investigated such the flow field, for a diagonal flow fan tittle study has been done. In this study, velocity fields at rotor Inlet in a high specific-speed diagonal flow fan were measured by use of a single slant hot-wire probe. These data were processed by using the "Double Phase-Locked Averaging"(DPLA) technique, i. e. phases of both the rotor blade and the stall cell were taken into account. The behaviors of stall cell at rotor inlet were visualized for the meridional, tangential and radial velocity.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.243-246
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• 1999

The displacement current measuring system used for detecting the dynamic behavior of monolayers at the air-water interface is described. It basically consists of a film balance, a pair of electrodes connected to each other through a sensitive ammeter. Here, one electrode is suspended in air and the other electrode is the water, With Maxwll-displacement-current-measuring method, the phase transitions of Poly(λ-benzyl- L-glutamate)(PBLG) on a water surface were detected, Displacement currents generated during the compression of monolayers of PBLG on the surface of water were investigated. As results, the displacement pick was generated when the area per molecule was about 15 $\AA$$^{2}$ in low pressure, and tit was generarted when the area per molecule about 27$\AA$$^{2}$ in high pressure.

• 대한기계학회논문집B
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• 제33권6호
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• pp.454-460
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• 2009

To analyze the mixture formation process of evaporating diesel spray is important for emissions reduction in actual engines. Then the effects of change in density of ambient gas on spray structure in high temperature and pressure field have been investigated in this study. The ambient gas density was changed from ${\rho}_a=5.0kg/m^3$ to ${\rho}_a=12.3kg/m^3$ with CVC(Constant Volume Chamber). Also, simulation study by modified KIVA-II code was conducted and compared with experimental results. The ambient temperature and injection pressure are kept as 700K and 72MPa, respectively. The images of liquid and vapor phase in the evaporating free spray were simultaneously taken by exciplex fluorescence method. As experimental results, with increasing ambient gas density, the tip penetration of the evaporating free spray decreases due to the increase in the drag force from ambient gas. The spatial structure of a diesel spray can be verified as 2-regions consisted of liquid with momentum decrease and vapor with large-scale vortex. The calculated results obtained by modified KIVA-II code show good agreements with experimental results.

• 융복합기술연구소 논문집
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• 제4권2호
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• pp.47-50
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• 2014

Voloxidation is a process for converting $UO_2$ into $U_3O_8$ while removing some volatile products in spent fuels (SF). Various oxidative gas conditions including air and mixture of Ar and $O_2$ could be adopted for the process. The gas flows into a reactor under high temperature ($>500^{\circ}C$) and components of SF are reacted with the gas. SF is composed of various components such as actinides, lanthanides, and alkali metals. Therefore, it is of significance to understand their behavior during the reactions for process development. However, due to the limit of available experiments, phase diagram analysis should be preceded. TPP diagram is constructed with respect to temperature-pressure-pressure. It shows a stable phase depending on partial pressures of gas components as well as temperature. In this work, we investigated TPP diagrams for actinides, lanthanides and other oxides to determine stable oxide forms under different gas conditions. The results would be used to set up a material balance under a pyroprocessing scheme of SF and compare the gas conditions for the optimization of fission products removal.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.315-323
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• 2009

Pressure oscillations triggered by the unstable interaction of dynamic flow features of the hydraulic turbine with the hydraulic plant system - including the electrical design - can at times reach significant levels and could lead to damage of plant components or could reduce component lifetime significantly. Such a problem can arise for overload as well as for part load operation of the turbine. This paper discusses an approach to analyze the overload high pressure oscillation problem using computational fluid dynamic (CFD) modeling of the hydraulic machine combined with a network modeling technique of the hydraulic system. The key factor in this analysis is the determination of the overload vortex rope volume occurring within the turbine under the runner which is acting as an active element in the system. Two different modeling techniques to compute the flow field downstream of the runner will be presented in this paper. As a first approach, single phase flow simulations are used to evaluate the vortex rope volume before moving to more sophisticated modeling which incorporates two phase flow calculations employing cavitation modeling. The influence of these different modeling strategies on the simulated plant behavior will be discussed.

• 한국초전도ㆍ저온공학회논문지
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• 제20권3호
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• pp.21-27
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• 2018

It is difficult to fabricate and maintain moving parts of expander at cryogenic temperature. This paper describes numerical analysis and experimental investigation on a cryogenic reciprocating expander without moving piston. An intake valve which takes high-pressure gas, and an exhaust valve which discharges low-pressure gas, are connected to a tube. The inside pressure of the tube is pulsated for work production. This geometric configuration is similar to that of pulse tube refrigerator but without regenerator. An orifice valve and a reservoir are installed to control the phase of the mass flow and the pressure. At the warm end, a heat exchanger rejects the heat which is converted from the produced work of the expanded gas. For the numerical analysis, mass conservation, energy conservation, and local mass function for valves are used as the governing equations. Before performing cryogenic experiments, we carried out the expander test at room temperature and compared the performance results with the numerical results. For cryogenic experiments, the gas is pre-cooled by liquid nitrogen, and then it enters the pulse tube expander. The experiments are controlled by the opening of the orifice valve. Numerical analysis also found the expander conditions that optimize the expander performance by changing the intake pressure and valve timing as well as the opening of the orifice valve. This paper discusses the experimental data and the numerical analysis results to understand the fundamental behavior of such a newly developed non-mechanical expander and elucidate its potential feature for cryogenic application.

• 자원환경지질
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• 제49권1호
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• pp.23-30
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• 2016

자연산 로소나이트(Ca-Lawsonite, $CaAl_2Si_2O_7(OH)_2{\cdot}H_2O$) 분말의 압력증가에 따른 변화와 구조적 특성을 소형 압력 발생장치인 다이아몬드 앤빌셀과 실시간 싱크로트론 X-선 회절실험을 통하여 확인하였다. 본 연구에서 시료에 적용한 압력은 1 기압에서 8 GPa 까지였으며 메탄올, 에탄올, 물의 혼합 용액을 압력 매개체로 하여 상온조건에서 실험하였고, 특이한 상전이나 압력하 부피변화의 이상현상은 발견되지 않은 가역적 압축특성을 관찰하였다. 최고압력까지 로소나이트는 결정성을 잃지 않는 것으로 확인되었고 압력증가에 따른 체적감소를 통해 체적탄성률($B_0$)을 계산해 본 결과 146(6) GPa로 도출되었다. 체적탄성률과 함께 계산된 선형압축률은 a-, b-, c-축에서 각각 0.0022, 0.0024, $0.0020GPa^{-1}$로 압력에 의한 부피감소는 대체적으로 3축이 같은 비율로 감소하는 것을 확인하였다.

• 한국정밀공학회지
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• 제26권10호
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• pp.81-88
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• 2009

Bellows is used to control temperature of a Joule-Thomson micro cryocooler. It is made of Nickelcobalt alloy that retains mechanical properties from cryogenic temperature to temperature of 570K. The geometry of bellows is an axisymmetric shell and Nitrogen with high pressure was charged at temperature of 293K. During cool-down process, the pressure and volume of Nitrogen are changed and must be satisfied with state equation. At cryogenic temperature, Nitrogen can exist as a part liquid and part vapor. Pressure-density-temperature behavior under this vaporliquid phase equilibrium is closely given by the Modified-Benedict-Webb-Rubin(MBWR) state equation. To evaluate deformation of bellows for temperature change, the numerical calculation of the volume within bellows and finite element analysis of bellows under internal pressure were iteratively performed until MBWR state equation is satisfied. The numerical results show that deformation of the bellows can be analyzed by the present method in a wide range of temperature including cryogenic temperature.