• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.5
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• pp.670-677
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• 1999

An analysis of generation and growth of multicomponent particles has been carried out to predict the size and composition distributions of particles generated in the Modified Chemical Vapor Deposition(MCVD) process. In MCVD process. scale-up of sintering and micro-control of refractive index may need the Information about the size and composition distributions of $SiO_2-GeO_2$ particles that are generated and deposited. The present work solved coupled steady equations (axi-symmetric two dimensions) for mass conservation, momentum balance. energy and species(such as $SiCl_4$, $GeCl_4$, $O_2$, $Cl_2$) conservations describing fluid flow. heat and mass transfer in a tube. Sectional method has been applied to obtain multi-modal distributions of multicomponent aerosols which vary in both radial and axial directions. Chemical reactions of $SiCl_4$ and $GeCl_4$ were included and the effects of variable properties have also been considered.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.351-351
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• 2011

Graphene has drawn great interests because of its distinctive band structure and physical properties[1]. A few of the practical applications envisioned for graphene include semiconductor applications, optoelectronics (sola cell, touch screens, liquid crystal displays), and graphene based batteries/super-capacitors [2-3]. Recent work has shown that excellent electronic properties are exhibited by large-scale ultrathin graphite films, grown by chemical vapor deposition on a polycrystalline metal and transferred to a device-compatible surface[4]. In this paper, we focussed our scope for the understanding the graphene growth at different conditions, which enables to control the growth towards the application aimed. The graphene was grown using chemical vapor deposition (CVD) with methane and hydrogen gas in vacuum furnace system. The grown graphene was characterized using a scanning electron microscope(SEM) and Raman spectroscopy. We changed the growth temperature from 900 to $1050^{\circ}C$ with various gas flow rate and composition rate. The growth condition for larger domain will be discussed.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.477-477
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• 2011

In this paper, we synthesize ZnO wire on Si substrate by catalyst-free thermal chemical vapor deposition (CVD). Each ZnO wire is grew up at different condition such as temperature and O2 flow rate. The Young's modulus of individual ZnO wires were estimated using quasi-static and dynamic measurements, as well as resonance frequency measurements. Using this system, current-voltage characteristics of each ZnO wire structure fabricated on a trench were measured. A new concept of electromechanical device structure combined with the piezoelectric effect of ZnO will be suggested in the end of this paper.

• The KSFM Journal of Fluid Machinery
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• v.7 no.1 s.22
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• pp.51-57
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• 2004

The waterhammer has recently become more important because the pumping stations were big and the systems conveying the fluid through the large and long transmission pipelines were complex. When the pumps are started or stopped for the operation or tripped due to the power failure, the hydraulic transients occur as a result of the sudden change in velocity As the pressure waves are propagating between the pumping station and the distributing reservoir, the pressure inside the pipe drops to the liquid vapor pressure with the pipeline profile, at which time a vapor cavity forms, and finally the column separation occurs. If the pressure in the pipe is less than the atmospheric pressure, the pipe can be collapsed and destroyed after the water columns separated by the vapor cavity rejoin. During the reverse flow, the pressure is so abnormally increased at the pumping station that the accident of flooding may happen due to the failure of system. In this paper, the field tests on the waterhammer by the startup, stoppage, and power failure of a centrifugal pump were carried out for Yongma transmission pumping station in Seoul. The experimental results were compared with that of the numerical calculations, in which results the procedure of controlled pump normal shut-down and the two-step closing mode of controlling the ball valve for pump emergency stop are proposed to reduce the pressure surge.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.433-433
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• 2013

Graphene, $sp^2$-hybridized 2-Dimension carbon material, has drawn enormous attention due to its desirable performance of excellent properties. Graphene can be applied for many electronic devices such as field-effect transistors (FETs), touch screen, solar cells. Furthermore, indium tin oxide (ITO) is commercially used and sets the standard for transparent electrode. However, ITO has certain limitations, such as increasing cost due to indium scarcity, instability in acid and basic environments, high surface roughness and brittle. Due to those reasons, graphene will be a perfect substitute as a transparent electrode. We report the graphene synthesized by inductive coupled plasma enhanced chemical vapor deposition (ICP-PECVD) process on Cu substrate. The growth was carried out using low temperature at $400^{\circ}C$ rather than typical chemical vapor deposition (CVD) process at $1,000^{\circ}C$ The low-temperature process has advantage of low cost and also low melting point materials will be available to synthesize graphene as substrate, but the drawback is low quality. To improve the quality, the factor affect the quality of graphene was be investigated by changing the plasma power, the flow rate of precursors, the scenario of precursors. Then, graphene film's quality was investigated with Raman spectroscopy and sheet resistance and optical emission spectroscopy.

• Fire Science and Engineering
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• v.24 no.4
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• pp.33-40
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• 2010

A numerical model considering the vapor pressure and the creep models, in the form of a analytical program, for tracing the behavior of high strength concrete (HSC) members exposed to fire is presented. The two stages, i.e., spalling procedure and fire resistance time, associated with the thermal, moisture flow, creep and structural analysis, for the prediction of fire resistance behavior are explained. The use of the analytical program for tracing the response of HSC member from the initial pre-loading stage to collapse, due to fire, is demonstrated. The validity of the numerical model used in this program is established by comparing the predictions from this program with results from others fire resistance tests. The analytical program can be used to predict the fire resistance of HSC members for any value of the significant parameters, such as load, sectional dimensions, member length, and concrete strength.

• Journal of Powder Materials
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• v.17 no.3
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• pp.223-229
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• 2010

Iron(Fe)-Molybdenum(Mo) alloyed nanoparticles and nanowires were produced by the chemical vapor condensation(CVC) process using the pyrolysis of iron pentacarbonyl($Fe(CO)_5$) and Molybdenum hexacarbonyl($Mo(CO)_6$). The influence of CVC parameter on the formation of nanoparticle, nanowire and size control was studied. The size of Fe-Mo alloyed nanoparticles can be controlled by quantity of gas flow. Also, Fe-Mo alloyed nanowires were produced by control of the work chamber pressure. Moreover, we investigated close correlation of size and morphology of Fe-Mo nanoparticles and nanowires with atomic quantity of inflow precursor into the electric furnace as the quantitative analysis. Obtained nanoparticles and nanowires were investigated by field emission scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction.

• Journal of Powder Materials
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• v.15 no.6
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• pp.496-502
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• 2008

Aluminum nitride (AlN) powders were prepared by the chemical vapor synthesis (CVS) process in the $AlCl_{3}-NH_{3}-N_{2}$ system. Aluminum chloride ($AlCl_3$) as the starting material was gasified in the heating chamber of $300^{\circ}C$. Aluminum chloride gas transported to the furnace in $NH_{3}-N_{2}$ atmosphere at the gas flow rate of 200-400ml/min. For samples synthesized between 700 and $1200^{\circ}C$, the XRD peaks corresponding to AlN were comparatively sharp and also showed an improvement of crystallinity with increasing the reaction temperature. In additions, the average particle size of the AlN powders decreased from 250 to 40 nm, as the reaction temperature increased.

• Journal of Hydrogen and New Energy
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• v.27 no.6
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• pp.727-736
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• 2016

Numerical simulations of n-heptane spray characteristics in a constant volume combustion chamber under diesel engine like conditions with increasing ambient gas density ($14.8-142kg/m^3$) and ambient temperature (800-1000 K) respectively were performed to understand the non-vaporizing and vaporizing spray behavior. The effect of fuel temperature (ranging 273-313 K) on spray characteristics was also simulated. In this simulation, spray modeling was implemented into ANSYS FORTE where the initial spray conditions at the nozzle exit and droplet breakups were determined through nozzle flow model and Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) model. Simulation results were compared with experimentally obtained spray tip penetration result to examine the accuracy. In case of non-vaporizing condition, simulation results show that with an increment of the magnitude of ambient gas density and pressure, the vapor penetration length, liquid penetration length and droplet mass decreases. On the other hand vapor penetration, liquid penetration and droplet mass increases with the increase of ambient temperature at the vaporizing condition. In case of lower injection pressure, vapor tip penetration and droplet mass are increased with a reduction in fuel temperature under the low ambient temperature and pressure.

• Journal of Hydrogen and New Energy
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• v.23 no.5
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• pp.521-529
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• 2012

Since the energy demand for refrigeration and air-conditioning has greatly increased all over the world, thermally activated refrigeration cycle has attracted much attention. This study carries out a performance analysis of a vapor compression cycle (VCC) driven by organic Rankine cycle (ORC) utilizing low-temperature heat source in the form of sensible heat. The ORC is assumed to produce minimum net work which is required to drive the VCC without generating an excess electricity. Effects of important system parameters such as turbine inlet pressure, condensing temperature, and evaporating temperature on the system variables such as mass flow ratio, net work production, and coefficient of performance (COP) are thoroughly investigated. The effect of choice of working fluid on COP is also considered. Results show that net work production and COP increase with increasing turbine inlet pressure or decreasing condensing temperature. Out of the five kinds of organic fluids considered $C_4H_{10}$ gives a relatively high COP in the range of low turbine inlet pressure.