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Computational Analysis of a Variable Ejector Flow

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Journal of Thermal Science 2006年第2期15卷 140-144页

作者： h.D. kim J.h. LEE T. SETOGUChI S.MATSUO School of Mechanical Engineering Andong National University 388 Songchun-dong Andong 760-749 Korea Department of Mechanical Engineering Saga University 1 Honjo Saga 840-8502 Japan

The present study addresses a variable ejector which can improve the ejector efficiency and control the re-circulation ratio under a fixed operating pressure ratio. The variable ejector is a facility to obtain specific recirculation ratio under a given operating pressure ratio by varying the ejector throat area ratio. The numerical simulations are carried out to provide an understanding of the flow characteristics inside the variable ejector. The sonic and supersonic nozzles are adopted as primary driving nozzles in the ejector system, and a movable cone cylinder, inserted into a conventional ejector-diffuser system, is used to change the ejector throat area ratio. The numerical simulations are based on a fully implicit finite volume scheme of the compressible, Reynolds-Averaged Navier-Stokes equations. The results show that the variable ejector can control the recirculation ratio at a fixed operating pressure ratio.

关键词： variable ejector ejector throat area ratio re-circulation ratio

high Temperature Mechanical Properties of Ni-Al-Cr Based Alloys for Advanced Die-Materials Applications

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Journal of Materials Science & Technology 2008年第3期24卷 305-308页

作者： W.Y.kim h.S.kim Y.G.Yoo I.D.Yeo Advanced Materials R&D Division Korea Institute of Industrial Technology7-47Songdo-dongYeonsu-gu

In this study, we report on advanced Ni3Al based high temperature structural alloys with Zr and B addition in order to apply in the fields of die-casting and high temperature press forming as die materials. Microstructures and mechanical properties of Ni3Al based intermetallic alloys produced by vacuum arc melting were investigated in terms of phase analysis by using a scanning electron microscope （SEM） equipped with an X-ray energy dispersive spectrometer （EDS）, an X-ray diffractometer （XRD） and tensile test. The duplex microstructural feature consisting of γ＇ matrix phase and small intermetallic dispersoids was observed to be distributed over the whole microstructure. The ultimate tensile strength of the present alloy was superior to commercial iron-based and Ni-based die-materials especially in the high temperature region.

关键词： Intermetallic Die material Alloying effect Mechanical property

Effects of Mo and Zr on Microstructure,Mechanical Properties and Wear Resistance of Fe-Al Based Alloys

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Journal of Materials Science & Technology 2008年第3期24卷 309-312页

作者： I.D.Yeo h.S.kim Y.G.Yoo W.Y.kim Advanced Materials R&D Division Korea Institute of Industrial Technology7-47Songdo-dongYeonsu-gu

In this work the microstructure, mechanical properties and wear resistance of Fe-Al based alloys with various alloying elements were studied. The microstructures were examined by optical and scanning electron microscopy （SEM） equipped with an energy dispersive X-ray spectroscope （EDS）. Two types of alloys were prepared by vacuum arc melting. One is Fe-28Al based alloys （D03 structured） with and without alloying elements such as Mo and Zr. The other one is Fe-35Al based alloys （B2 structured） produced with the same manner. For both types of alloys, Mo addition had found to exhibit an equiaxed microstructure, while dendritic structure was observed to show the effect of Zr addition. These microstructural features were more evinced with increasing content of alloying element. Concerning the mechanical properties and wear resistance, Fe-35Al based alloys were superior to Fe-28Al based alloys over the whole temperature range investigated.

关键词： Fe-Al alloy Intermetallic Mechanical properties Wear resistance

The efect of the couple stress parameter and Prandtl number on the transient natural convection flow over a vertical cylinder

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Acta Mechanica Sinica 2013年第5期29卷 649-656页

作者： h.P.Rani G.Janardhana Reddy Chang Nyung kim Department of Mathematics National Institute of TechnologyWarangal-506004 AP India Department of Mechanical Engineering College of Advanced Technology (Industrial Liaison Research Institute)Kyung Hee UniversityGyeonggi-do 446-701 Korea

An analysis is performed to study transient free convective boundary layer flow of a couple stress fluid over a vertical cylinder, in the absence of body couples. The solution of the time-dependent non-linear and coupled governing equations is carried out with the aid of an unconditionally stable Crank-Nicolson type of numerical scheme. Numerical results for the steady-state velocity, temperature as well as the time histories of the skin-friction coefficient and Nus- selt number are presented graphically and discussed. It is seen that for all flow variables as the couple stress control parameter, Co, is amplified, the time required for reaching the temporal maximum increases but the steady-state decreases.

关键词： Couple stress fluid Natural convection Vertical cylinder Finite difference method

Plasma density measurement and downstream etching of silicon and silicon oxide in Ar/NF3 mixture remote plasma source

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Plasma Science and Technology 2019年第6期21卷 52-57页

作者： h J YEOM D h ChOI Y S LEE J h kim D J SEONG S J YOU h C LEE korea Research Institute of Standards and Science(kRISS) Daejeon 34113 Republic of Korea Department of Physics Chungnam National University Daejeon 34134 Republic of Korea

In this study,plasma density measurements were performed near the plume region of the remote plasma source (RPS) in Ar/NF3 gas mixtures using a microwave cutoff *** measured plasma density is in the range of 1010-1011 cm-3 in the discharge conditions with RPS powers of 2-4 kW and gas pressures of 0.87-4 *** plasma density decreased with increasing gas pressures and RPS powers under various Ar/NF3 mixing *** decrease in the plasma density measured at the fixed measurement position (plume region) can be understood by the reduction of the electron energy relaxation length with increases in the gas pressures and mixing ratio of NF3/(Ar/NF3).We also performed downstream etching of silicon and silicon oxide films in this *** etch rate of the silicon films significantly increases while the silicon oxide is slightly etched with the gas pressures and *** was also found that the etch rate strongly depends on the wafer position on the processing chamber electrode,and that the etch selectivity reached 96-131 in the discharge conditions of RF powers (3730-4180 W) and gas pressures (3.6-4 Torr).

关键词： remote plasma source electron density cutoff probe downstream etch

Study of Thermal and hydraulic Performances of Circular and Square Ribbed Rough Microchannels Using LBM

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Journal of Thermal Science 2015年第6期24卷 549-556页

作者： M.A.Taher h.D.kim Y.W Lee Department of Mechanical and Automotive Engineering Pukyong National University Department of Mechanical Engineering Andong National University

The effects of roughness geometries and relative roughness height at the slip flow regime to investigate the thermal and hydraulic performances of microchannel have been considered in the present article using a thermal Lattice Boltzmann Method(TLBM).A two dimensional 9-bit(D2Q9)single relaxation time(SRT)model is used to simulate this *** micro-flows,the local density variation is still relatively small,but the total density changes,therefore,in order to account this density variation and its effect on the kinematic viscosityν,a new relaxation time proposed by Niu et al.[13]is *** roughness geometry is modeled as a series of square and circular riblets with a relative roughness height from 0%to 10%of the channel *** friction coefficients in terms of Poiseuille number(Pn)and the dimensionless heat transfer rate in terms of Nusselt number(Nu)have been discussed in order to analyze the roughness *** thermal-hydraulic performance(η)is calculated considering the simultaneous effects of thermal and fluid friction(pressure drop)at the slip flow regime at knudsen number,kn,ranging from 0.01 to 0.10 with other controlling parameters for both kind of *** results have been compared with previous published works and it is found to be in very good agreement.

关键词： Lattice-Boltzmann Friction factor knudsen number Surface Roughness

Unassisted overall water splitting with a solar-to-hydrogen efficiency of over 10% by coupled lead halide perovskite photoelectrodes

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Carbon Energy 2023年第1期5卷 134-143页

作者： Ryan Rhee Tae G.kim Gyu Y.Jang Gwangmin Bae Jung h.Lee Sunje Lee Sungsoon kim Seokwoo Jeon Jong h.Park Department of Chemical and Biomolecular Engineering Yonsei UniversitySeoulRepublic of Korea Department of Materials Science and Engineering KAIST Institute for The Nanocentury(KINC)Korea Advanced Institute of Science and Technology(KAIST)DaejeonRepublic of Korea

hydrogen is a promising future sustainable fuel candidate with boundless *** into photoelectrochemical(PEC)water splitting based on a lead halide perovskite(LhP)has progressed significantly with the aim of more efficient solar hydrogen ***,we unite a well-known photo-absorbing LhP with cost-effective water-splitting catalysts,and we introduce two types of monolithic LhP-based PEC devices that act as a photocathode and a photoanode for the hydrogen evolution reaction and oxygen evolution reaction,leading to efficient unbiased overall water *** the integration of these two monolithic LhP-based photoelectrodes,an unbiased solar-to-hydrogen conversion efficiency of 10.64%and a photocurrent density of 8.65 mA cm^(−2) are achieved.

关键词： perovskite photoelectrochemical cell photoelectrode unassisted

Nanotube-Based Chemical and Biomolecular Sensors

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Journal of Materials Science & Technology 2008年第4期24卷 578-588页

作者： J.koh B.kim S.hong h.Lim h.C.Choi Department of Physics and Astronomy Seoul National University Shillim-Dong Kwanak-Gu Seoul 151-747 Korea Department of Chemistry Pohang University of Science and Technology San 31 Hyoja-Dong Nam-Gu Pohang 790-784 Korea

We present a brief review about recent results regarding carbon nanotube （CNT）-based chemical and biomolecular sensors. For the fabrication of CNT-based sensors, devices containing CNT channels between two metal electrodes are first fabricated usually via chemical vapor deposition （CVD） process or ＂surface programmed assembly＂ method. Then, the CNT surfaces are often functionalized to enhance the selectivity of the sensors. Using this process, highly-sensitive CNT-based sensors can be fabricated for the selective detection of various chemical and biological molecules such as hydrogen, ammonia, carbon monoxide, chlorine gas, DNA, glucose, alcohol, and proteins.

关键词： Chemical vapour deposition Carbon nanotubes Sensors Biological molecules Surface programmed assembly

Experimental Status of the hANBIT Facility

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Plasma Science and Technology 2004年第4期6卷 2367-2370页

作者： S.J.Yoo M.kwon J.G.Bak k.Choh I.S.Choi J.h.Choi J.W.Choi A.C.England J.hong h.S.Jeon h.G.Jhang J.S.Ju M.Jung J.Y.kim S.S.kim W.h.ko k.Y.kwak M.C.kyum B.J.Lee D.k.Lee J.h.Lee h.G.Lee S.G.Lee T.Lho h.k.Na B.h.Park M.k.Park D.C.Seo S.h.Seo J.h.Yeom J.S.Yoon k.I.You korea Basic Science Institute Daejeon305-333Korea hanbit User Group

hANBIT is a magnetic mirror confinement device. Recent physics experimentshave been mainly focused on identifying discharge characteristics and on getting stable plasmaproduction and operation modes, by using a 500 kW slot antenna system at a fixed RF frequency of 3.5Mhz and varying discharge conditions such as fueling rate, RF power, and B-field intensity incentral cell. Two distinct operation modes are found to be very sensitive to the RF power as well asthe ratio of the RF frequency to the ion cyclotron frequency. A MhD interchange mode of m = - 1 isclearly observed and the stabilizing mechanism can be explained by the sideband coupling theory.

关键词： mirror discharge stabilization