• Journal of Korea Foundry Society
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• v.17 no.5
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• pp.494-501
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• 1997

In order to manufacture large rod preforms of 2014 Al alloy with a good mechanical property by spray forming method, it was spray-formed at a droplet temperature of $715^{\circ}C$, a droplet flight distance of 400mm, and a spraying angle of $35^{\circ}$. The rod preforms were extruded at $397^{\circ}C$ with the die temperature of $420^{\circ}C$ under the hot extrusion ratio 21:1 and T6 heat treatment was performed. The 2014 Al alloys cast by hot top process were also extruded and heat-treated at the same condition as a reference material. Microstructural observation and tensile test were carried out to investigate the effects of extrusion on microstructure and mechanical property of spray-formed Al alloy. Spray-formed Al alloys had many porosities due to inappropriate process conditions such as long droplet flight distance and low droplet temperature but have fine equiaxed grain. These porosities were reduced with decreasing in grain size by hot extrusion. Ultimate tensile strength and yield strength of spray formed-extruded 2014 Al alloy were inferior to those of the normal cast-extruded 2014 Al alloy, but elongations were superior. The control of porosity was important to get spray formed preform with a good mechanical property.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.107-110
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• 1999

The ultrasonic spray method was employed to make (Y,Gd)BO$_3$:Eu Phosphor, and its optical properties under 147nm VUV and 254 nm UV excitations were characterized and then compared with that produced by the solid-state reaction. The mixed solution of acetate hydrates of Y, Gd, Eu and boric acid diluted in water or methanol was used as the precursor fur the spray. It was found that (Y,Gd)BO$_3$:Eu phosphor made by this ultrasonic spray had a spherical shape and fine particle size of 1${\mu}{\textrm}{m}$. The crystalline structure for the as-sprayed phosphor was amorphous, but it converted into the same polycrystalline phase of solid state reaction after post heat treatment at 110$0^{\circ}C$ for 2hr. The emitting intensity under VUV and UV excitations for the spray-formed (Y,Gd)BO$_3$:Eu phosphor, however, was inferior to the later one. The excitation spectra were also studied and compared under VUV and UV excitations to explain the change of emitting intensity with Gd substitution in (Y$_{1-x}$ Gd$_{x}$)BO$_3$:Eu Phosphors made by spray and solid state reaction.on.

• Archives of Metallurgy and Materials
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• v.64 no.2
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• pp.607-611
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• 2019

Thermal/cold spray deposition were used for additive manufacture of oxide dispersion strengthened (ODS) steel layers. Mechanically alloyed F/M ODS steel powders (Fe(bal.)-10Cr-1Mo-0.25Ti-0.35Y2O3 in wt.%) were sprayed by a high velocity oxygen fuel (HVOF) and cold spray methods. HVOF, as a thermal method, was used for manufacturing a 1 mm-thick ODS steel layer with a ~95% density. The source to objective distance (SOD) and feeding rate were controlled to achieve sound manufacturing. Y₂Ti₂O₇ nano-particles were preserved in the HVOF sprayed layer; however, unexpected Cr₂O₃ phases were frequently observed at the boundary area of the powders. A cold spray was used for manufacturing the Cr₂O₃-free layer and showed great feasibility. The density and yield of the cold spray were roughly 80% and 45%, respectively. The softening of ODS powders before the cold spray was conducted using a tube furnace of up to 1200℃. Microstructural characteristics of the cold sprayed layer were investigated by electron back-scattered diffraction (EBSD), the uniformity of deformation amount inside powders was observed.

• Journal of Mechanical Science and Technology
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• v.16 no.7
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• pp.986-998
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• 2002

Flow and spray characteristics are critical factors that affect the performance and exhaust emissions of a direct injection diesel engine. It is well known that the swirl control system is one of the useful ways to improve the fuel consumption and emission reduction rate in a diesel engine. However, until now there have only been a few studies on the effect of flow on spray. Because of this, the relationship between the flow pattern in the cylinder and its influence on the behavior of the spray is in need of investigation. First, in-cylinder flow distributions for 4-valve cylinder head of DI (Direct Injection) Diesel engine were investigated under steady-state conditions for different SCV (Swirl Control Valve) opening angles using a steady flow rig and 2-D LDV (Laser Doppler Velocimetry). It was found that swirl flow was more dominant than that of tumble in the experimented engine. In addition, the in-cylinder flow was quantified in terms of swirl/tumble ratio and mean flow coefficient. As the SCV opening angle was increased, high swirl ratios more than 3.0 were obtained in the case of SCV -70° and 90°. Second, spray characteristics of the intermittent injection were investigated by a PDA (Phase Doppler Anemometer) system. A Time Dividing Method (TDM) was used to analyze the microscopic spray characteristics. It was found that the atomization characteristics such as velocity and SMD (Sauter Mean Diameter) of the spray were affected by the in-cylinder swirl ratio. As a result, it was concluded that the swirl ratio improves atomization characteristics uniformly.

• Journal of the Microelectronics and Packaging Society
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• v.13 no.3 s.40
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• pp.33-38
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• 2006

Aerosol slurry composed of dielectric materials, distilled water, and deflocculants was sprayed on the substrates, through a high-pressure spray gun as an aerosol. The coated layers were cofired together with $Al_{2}O_{3}$ substrates and green sheets on which the inner connectors were printed. Although the coating rate of coated layers strongly depended on slurry viscosity, spray shape, and the pressure of the spray gun, the coated density was not changed. Buried conductors were maintained as printed by high pressure spray coating method, because the pressing process was not used. At the optimum condition of air controller step 3-4 and slurry viscosity c.p 2000-4000, dense and uniform layers could be achieved. Comparing with conventional lamination process using green sheets, spray coating method enabled thin dielectric layers of $20{\sim}50{\mu}m$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.6 s.249
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• pp.553-559
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• 2006

Most diesel injector, which is currently used in high-pressure common rail fuel injection system of diesel engine, is driven by the solenoid coil energy for its needle movement. The main disadvantage of this solenoid-driven injector is a high power consumption, high power loss through solenoid coil and relatively fixed needle response's problem. In this study, a prototype piezo-driven injector, as a new injector mechanism driven by piezoelectric energy based on the concept of inverse piezo-electric effect, has been designed and fabricated to know the effect of piezo-driven injection processes on the diesel spray structure and internal nozzle flow. Firstly we investigated the spray characteristics in a constant volume chamber pressurized by nitrogen gas using the back diffusion light illumination method for high-speed temporal photography and also analyzed the inside nozzle flow by a fully transient simulation with cavitation model using VOF(volume of fraction) method. The numerical calculation has been performed to simulate the cavitating flow of 3-dimensional real size single hole nozzle along the injection duration. Results were compared between a conventional solenoid-driven injector and piezo-driven injector, both equipped with the same micro-sac multi-hole injection nozzle. The experimental results show that the piezo-driven injector has short injection delay and a faster spray development and produces higher injection velocity than the solenoid-driven injector. And the predicted simulation results with the degree of cavitation's generation inside nozzle for faster needle response In a piezo-driven injector were reflected to spray development in agreement with the experimental spray images.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.354-355
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• 2006

We manufactured photoelectrode of dye-sensitized solar cells (DSC) by using three methods such as squeeze method, spray method, and combination method (squeeze method first, spray method second). We examined how the morphology of an electrode's surface, the pore between particles, and condensation have an effect on an open-circuit voltage, photocurrent, fill factor, and energy conversion efficiency. Open-circuit voltage of dye-sensitized solar cells manufactured by using three methods is about 0.66V when the photoelectrode of the three DSCs is about $5{\mu}m$ thick. Photocurrent and fill factor and conversion efficiency of DSC manufactured by using squeeze method is 18.5 and 34 and 7.8, respectively. Photocurrent and fill factor and conversion efficiency of DSC manufactured by using spray method is 3.62 and 62 and 2.8, respectively. Photocurrent and fill factor and conversion efficiency of DSC manufactured by using combination method is 10.7 and 46 and 5.9, respectively. In conclusion, we find that the combination method is better than the other two methods in such respects as energy conversion efficiency and fill factor.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3062-3067
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• 2007

HVOF thermal spray guns are now being widely used to produce protective coatings, on the surfaces of engineering components. HVOF technology employs a combustion process to heat the gas flow and melt the coating materials which are particles of metals, alloys or cermets. Particle flow which is accelerated to high velocities and combustion gas stream are deposited on a substrate. In order to obtain good quality coatings, the analysis of torch design must be performed. The reason is that the design parameters of torch influence gas dynamic behaviors. In this study, numerical analysis is performed to predict the gas dynamic behaviors in a HVOF thermal spray gun with various torch shapes. The CFD model is used to deduce the effect of changes in nozzle geometry on gas dynamics. Using a commercial code, FLUENT which uses Finite Volume Method and SIMPLE algorithm, governing equations have been solved for the pressure, velocity and temperature distributions in the HVOF thermal spray torch.

• Journal of ILASS-Korea
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• v.1 no.1
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• pp.55-62
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• 1996

In a fuel injection engine, atomization of liquid fuel and mixture formation process has influenced(or affected) directly on the engine performance and pollutant emission. In this study, the characteristics of fuel spray and the behaviors of secondary atomization developed at the downstream of the valves were investigated using an image processing method. Solid and perforated valves are chosen in order to evaluate the valve performance in terns of air flow rate, valve opening angle and valve shape. Experimental results clearly indicate that the spray atomization quality can be improved by increasing the perforated rat io and the blockage rat io in the perforated valve, the characteristics of spray atomization is improved by using the perforated valve with high perforated rat io and blockage ratio.

• Agricultural and Biosystems Engineering
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• v.1 no.1
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• pp.16-21
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• 2000

Measurement of spray deposit is necessary for evaluation of a chemical application technology. However it is not easy and time consuming. A simple method for measuring the deposition amount of spray using a tracer and a spectrophotometer was developed. Various materials were tested to determine an adequate tracer. Food dye was selected as a tracer, because it was cheep and easily treatable. Using NIRS(Near Infrared Reflection Spectrophotometer), a regression curves between maximum absorbance of a solution and concentration of the tracer were obtained. Yellow food dye solution showed a peak of spectrum at 452 nm, and absorbance of peak showed a tendency to increase as concentration increased. Green or pink food dye were tested and judged to be good tracers. However, tracer concentration should not exceed certain limits in order to measure maximum absorption. Using spraying liquid with known tracer concentration and known amount of washing liquid, spray deposit amount on real targets on leaves could be estimated at less than 13% error level.