• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.101-102
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• 2014

Rising oil price and environmental problems are causing automotive industry to increase fuel efficiency. Improved fuel efficiency in gasoline engine was made possible by development of DISI gasoline engine. Since fuel is injected inside cylinder directly, in-cylinder temperature can be reduced than multi-port injection engine and this leads to increased compression ratio. However, engine performance is largely dependent on mixture formation process due to in-cylinder fuel injection. Especially for spray guided and air guided DISI gasoline engine, injection direction is important factor to mixture preparation. It is because interaction between intake flow and spray affect fuel-air mixture. Hence, in this study, mixture formation characteristics were analyzed by varying injection direction using KIVA 3V release2 code. Residual gas was considered for assuming combustion. Therefore, initial condition for in-cylinder temperature was set equal to the end state of exhaust stroke of combustion cycle. Since angle between intake air flow direction and spray direction affects fluid flow and evaporation field, mixture distribution was affected by fuel injection direction dominantly.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.507-510
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• 2004

Oblique ion-induced secondary electron emission coefficient(${\gamma}$) with low energy ..and work function ${\phi}_{\omega}$(${\theta}$ = 0 and ${\theta}$ = 20) of the MgO thin film in AC-PDPs has been measured by ${\gamma}$-FIB system. The MgO thin film has been deposited from sintered material under electron beam evaporation method. The energy of $He^+$ ions used has been ranged from 50eV to 150eV. Oblique ion beam has been chosen to be 10 degree, 20 degree and 30 degree. It is found that the higher secondary electron emission coefficient(${\gamma}$) has been achieved by the higher oblique ion beam up to inclination angle of 30 degree than the perpendicular incident ion beam.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1349_1350
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• 2009

Thin films of pp(ST-Co-VA) were fabricated by plasma deposition polymerization (PVDPM) technique. Properties of the plasma polymerized pp(ST-Co-VA) thin films were investigated for application to semiconductor device as insulator. Thickness, dielectric property, composition of the pp(ST-Co-VA) thin films were investigated considering the relationship with preparation condition such as gas pressure and deposition time. In order to verify the possibility of application to organic thin film transistor, a pentacene thin film was deposited on the pp(ST-Co-VA) insulator by vacuum thermal evaporation technique. Crystalline property of the pentacene thin film was investigated by XRD and SEM, FT-IR. Surface properties at the pp(ST-Co-VA)/pentacene interface was investigated by contact angle measurement. The pp(ST-Co-VA) thin film showed a high-k (k=4.6) and good interface characteristic with pentacene semiconducting layer, which indicates that it would be a promising material for organic thin film transistor (OTFT) application.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.5
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• pp.30-37
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• 2007

Dimethyl Ether(DME) is an alternative fuel for diesel engine, it is renewable and offers potential reductions in emissions. This work was conducted to figure out the macroscopic behavior and the atomization characteristics of DME using a common-rail injection system. The macroscopic behavior was visualized with the spray visualization system composed of a Nd;YAG laser and an ICCD camera. The atomization characteristics were investigated in terms of axial mean velocity, Sauter mean diameter(SMD) and droplet distributions obtained from a phase Doppler particle analyzer(PDPA) system. In this study, it was revealed that the macroscopic behavior and the atomization characteristics of DME are similar compared with commercial diesel fuel. However, DME fuel has a shorter spray tip penetration and a small SMD due to the effect of evaporation characteristics.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.1
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• pp.183-192
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• 2014

In this work, the mixture formation and atomization characteristics of biodiesel fuel were reviewed under various test conditions for the optimization of compression-ignition engine fueled with biodiesel. To achieve these, the effect of nozzle caviting flow, group-hole nozzle geometry and injection strategies on the injection rate, spray evolution and atomization characteristics of biodiesel were studied by using spray characteristics measuring system. At the same time, the fuel heating system was installed to obtain the effect of fuel temperature on the biodiesel fuel atomization. It was revealed that cavitation in the nozzle orifice promoted the atomization performance of biodiesel. The group-hole nozzle geometry and split injection strategies couldn't improve it, however, the different orifice angles which were diverged and converged angle of a group-hole nozzle enhanced the biodiesel atomization. It was also observed that the increase of fuel temperature induced the quick evaporation of biodiesel fuel droplet.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.3
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• pp.363-372
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• 2000

An experiment was carried out to evaluate the heat transfer enhancement and the pressure drop characteristics for liquid nitrogen using wire-coil-insert technique under horizontal two-phase conditions. The tube inner diameters were 8 mm and 15 mm, respectively and the tube length was 4.7 m. The helix angle of the wire coil insert was $50^{\circ}$ and its length was 4.7 m. Heat transfer coefficients for both the plain and the enhanced test tubes were calculated from the measurements of temperatures, flow rates and pressure drops. A correlation in a power-law relationship of the Nusselt number, Reynolds number and Prandtl number for the heat transfer was proposed which can be available for design of cryogenic heat exchangers. The correlation showed that heat transfer coefficients for the wire-coil inserts were much higher than those for plain tubes, increased by more than $1.8{\sim}2.0$ times depending upon the range of the equivalent Reynolds number. The correlation was compared with other various correlations in the turbulent flow conditions.

• Progress in Superconductivity
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• v.11 no.2
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• pp.96-99
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• 2010

We measured electrical shot noise in a metal-insulator-metal tunnel junction, which was made by using electron-beam lithography and double-angle evaporation technique. Since the dependence of the shot noise on bias voltage and temperature is theoretically well known, we can determine the temperature of the junction by measuring the noise as the voltage across the junction is changed. A cryogenic low noise amplifier was used to amplify the noise signal in the frequency range of 600-800 MHz, which enabled fast measurement of noise signal and thus temperature. With further study, this method could be useful for primary thermometry in cryogenic temperatures.

• Journal of Hydrogen and New Energy
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• v.24 no.5
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• pp.444-450
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• 2013

The distribution performance of refrigerant distributors in air conditioner evaporators was examined numerically and experimentally. Internal flow analysis of the distributor by CFD found that the distance from the socket to the cone, the angle of the cone and the base area of the cone were the most important factors affecting refrigerant distribution ability and vortex creation. To enhance distribution performance, two distributors with improved internal structures were designed. To test these new structures, distribution performance was also analyzed by CFD and an empirical experiment was carried out using the water-nitrogen. Experimental results on the distribution fraction of each distributor hole showed a good agreement with the results of the CFD analysis. Thus, the new design of the distributors enhanced distribution performance of the refrigerant distributors.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.357.1-357.1
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• 2014

Superhydrophobic WOx nanowire (NW) arrays were fabricated using a thermal evaporation and surface chemistry modification methods by self-assembled monolayer (SAM). As-prepared non-wetting WOx NWs surface shows water contact angle of $163.2^{\circ}$ and has reliable stability in underwater conditions. Hence the superhydrophobic WOx NWs surface exhibits silvery surface by total reflection of water layer and air interlayer. The stability analysus of underwater superhydrophobicity of WOx NWs arrays was conducted by changing hydrostatic pressure and surface energy of WOx NWs arrays. The stability of superhydrophobicity in underwater conditions decreased exponentially as hydrostatic pressure applied to the substrates increased3. In addition, as surface energy decreased, the underwater stability of superhydrophobic surface increased sharply. Specifically, sueprhydrophobic stability increased exponentially as surface energy of WOx NWs arrays was decreased. Based on these results, the models for explaining tendencies of superhydrophobic stability underwater resulting from hydrostatic pressure and surface energy were designed. The combination of fugacity and Laplace pressure explained this exponential decay of stability according to hydrostatic pressure and surface energy. This study on fabrication and modeling of underwater stability of superhydrophobic W18O49 NW arrays will help in designing highly stable superhydrophobic surfaces and broadening fields of superhydrophobic applications even submerged underwater.

• Journal of Power System Engineering
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• v.7 no.3
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• pp.74-79
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• 2003

Alumina($Al_2O_3$) and Al 6061 were brazed by using Al-12wt% Si filler metal in a high vacuum environment. The interfacial microstructure and mechanical properties of the joints were investigated. The results obtained were as follows. (1) The maximum tensile strength of 54Mpa was acquired at the processing conditions of high vacuum ($3{\times}10^{-6}Torr$), $620^{\circ}C$ and 10min, but this condition will not be used in the industrial area due to high evaporation of Al alloy composition. (2) Reaction products for holding time and brazing temperature worked as stress relieve layer and the fractures after the mechanical properties test were occurred to the ceramic side or reaction layer. (3) The glancing angle X-ray diffraction analysis for the reaction product of $Al_2O_3/Al$ 6061 were processed. the joint strengths were low due to existed $Al_2Si_5\;and\;SiO_2$.