• Korean Journal of Metals and Materials
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• v.46 no.6
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• pp.363-369
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• 2008

Effects of top coat morphology and thickness on thermal fatigue behavior of thermal barrier coatings (TBC) were investigated in this study. Thermal fatigue tests were conducted on three coating specimens with different top coat morphology and thickness, and then the test data were compared via microstructures, cycles to failure, and fracture surfaces. In the air plasma spray specimens (APS1, APS2), top coat were 200 and $300{\mu}m$ respectively. The thickness of top coat was about $700{\mu}m$ in the perpendicular cracked specimen (PCS). Under thermal fatigue condition at $1,100^{\circ}C$, the cycles to top coat failure of APS1, APS2, and PCS were 350, 560 and 480 cycles, respectively. The cracks were initiated at the interface of top coat and thermally grown oxide (TGO) and propagated into TGO or top coat as the number of thermal fatigue cycles increased. For the PCS specimen, additive cracks were initiated and propagated at the starting points of perpendicular cracks in the top coat. Also, the thickness of TGO and the decrease of aluminium concentration in bond coat do not affect the cycles to failure.

• Journal of the Korea Society of Computer and Information
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• v.28 no.2
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• pp.209-216
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• 2023

This paper aims to develop a model to estimate the paint thickness in a shipyard spray painting according to changes of spraying distance and speed. We acquired the experimental datasets of five different conditions with respect to the spraying distance and speed using a painting robot. In addition, we applied a preprocessing step to handle noises which might be caused by various reasons such as a nozzle damage. Our method is to transform a thickness function of a specified spraying distance and speed into another function of an unknown spraying and speed. We observed that the proposed method shows more stable and more accurate predictions compared with an artificial neural network-based approach.

• Journal of Powder Materials
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• v.28 no.4
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• pp.310-316
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• 2021

The effects of different spray angles (90°, 85°, 80°) on the microstructure and mechanical properties of a Y₂O₃ coating layer prepared using the atmospheric plasma spray (APS) process were studied. The powders employed in this study had a spherical shape and included a cubic Y₂O₃ phase. The APS coating layer exhibited the same phase as the powders. Thickness values of the coating layers were 90°: 203.7 ± 8.5 ㎛, 85°: 196.4 ± 9.6 ㎛, and 80°: 208.8 ± 10.2 ㎛, and it was confirmed that the effect of the spray angle on the thickness was insignificant. The porosities were measured as 90°: 3.9 ± 0.85%, 85°: 11.4 ± 2.3%, and 80°: 12.7 ± 0.5%, and the surface roughness values were 90°: 5.9 ± 0.3 ㎛, 85°: 8.5 ± 1.1 ㎛, and 80°: 8.5 ± 0.4 ㎛. As the spray angle decreased, the porosity increased, but the surface roughness did not show a significant difference. Vickers hardness measurements revealed values of 90°: 369.2 ± 22.3, 85°: 315.8 ± 31.4, and 80°: 267.1 ± 45.1 HV. It was found that under the condition of a 90° angle with the lowest porosity exhibited the best hardness value. Based on the aforementioned results, an improved method for the APS Y₂O₃ coating layer was also discussed.

• Journal of ILASS-Korea
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• v.27 no.2
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• pp.77-83
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• 2022

In this study, the thickness of the liquid sheet formed by a low speed impinging jet onto a flat plate was measured by the direct contact method. The spatial distribution characteristics of the sheet thickness in the radial and circumferential directions, and the effects of jet velocity and liquid viscosity were analyzed. The measurement results were compared with the theoretical predictions. The wavy surface was observed in the case of low viscosity water, but not in the high viscosity aqueous glycerol solutions. The sheet thickness increased as the circumferential angle increased or the distance from the impinging point increased, but the thickness decreased as the circumferential angle increased around the impinging point. As the jet speed increased, the sheet thickness decreased, and the sheet thickness increased as the liquid viscosity increased. Comparison with the theoretical predictions showed that the measurement results agreed well in the case of low viscosity water or high viscosity liquids around the impinging point. The distribution characteristics of the sheet thickness can provide useful means for prediction of spray characteristics in splash plate injectors.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.3
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• pp.131-137
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• 2005

Ultra high pressure injection equipment was developed to estimate and analyze the spray characteristics in ultra high pressure injection. Spray patterns were visualized by schlieren method and analyzed in ultra high pressure. Spray tip penetration, spray thickness, spray volume, and entrained air mass increased with the increase of the injection pressure. But over 2,800 bars of the injection pressure region, it was shown that the rate of improvement was not increased remarkably ,and the spray characteristics such as spray penetration, volume, and entrained air mass were reversed and got worse at 4,140 bars.

• Journal of ILASS-Korea
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• v.1 no.4
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• pp.24-31
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• 1996

This study addresses the behavior characteristics of diesel spray injected on the impinging disk with the room temperature. The models of impinging spray are the stick, the reflect and the wall jet model In the initiative of the fuel injection the impinging spray was the reflect model. because the momentum of droplets was very large. This model developed to the wall jet model according to the time approaches. On the low temperature disk the fuel film was made by the attachment of the droplets with low Weber number. The thickness of impinging spray was increased when the disk approached to the nozzle tip. Mathematical analysis for calculation with the behavior of impinging spray have to consider the reflecting effect and the influence of the fuel film.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.5
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• pp.25-32
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• 2000

In this paper, experiments investigating the high-temperature region heat transfer coefficients for the spray cooling of hot flat plates were performed by down spray water using flat spray nozzles. The heat transfer surface is made of copper and is 100mm in length and 40mm in width and 15mm in thickness. The experimental condition of spray are as follows: temperatures of the water droplets are T=20~$80^{\circ}C$ and droplets volume fluxes are D=0.001565~0.010438$m^3/m^2s$. Next, correlating equations for the heat transfer characteristics of spray cooling in the high temperature region are developed from the effects of droplets volume flux and the surface temperature of heat transfer plate.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.919-924
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• 2000

Spray impingement model and fuel film formation model were developed and incorporated into the computational fluid dynamics code, STAR-CD. The spray/wall interaction process were modelled by considering the change of behaviour with surface temperature condition and fuel film formation. We divided behaviour of fuel droplets after impingement into stick, rebound and splash using Weber number and parameter K. Spray impingement model accounts for mass conservation, energy conservation and heat transfer to the impinging droplets. A fuel film formation model was developed by Integrating the continuity, the Navier-Stokes and the energy equations along the direction of fuel film thickness. The validation of the model was conducted using diesel spray experimental data and gasoline spray impingement experiment. In all cases, the prediction compared reasonably well with experimental results. Spray impingement model and fuel film formation model have been applied to a direct injection diesel engine combustion chamber.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.4
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• pp.304-311
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• 2006

Experiments on evaporative spray cooling on the square plate heaters with plain or micro-porous coated surfaces were performed in this study. Micro-porous coated surfaces were made by using DOM [Diamond particle, Omegabond 101, Methyl-Ethyl-Keton] method. In case of purely air-jet cooling, the micro-porous coating doesn't affect the cooling capacity. In spray cooling three different flow patterns (complete wetting, evaporative wetting, dryout) are observed on both plain and micro-porous coated surfaces. The effects of various operating conditions, such as water flow rate, particle size, and coating thickness were investigated on the micro-porous coated surfaces. It is found that the level of surface wetting is an important factor to determine the performance of spray cooling. It depends on the balance between absorbed liquid amount by capillary force over porosity and the evaporative amount. The micro-porous coated surface has largest cooling capacity, especially in the evaporative wetting zone. It is found that the effects of liquid flow rate and coating thickness are significant in evaporative wetting zone, but are not in complete wetting and dryout zones.

• Journal of the Korean Ceramic Society
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• v.28 no.3
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• pp.197-204
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• 1991

The photoelectrochemical conversion in SnO2 films deposited by spray pyrolysis using SnCl4-alcohol solution and N2 gas has been studied. The photocurrent increases with increasing deposition temperature up to 40$0^{\circ}C$ and then decreases, and the electron affinity decreases as the deposition temperature increases to 40$0^{\circ}C$. As the concentration of the spray solution increases, the photocurrent reaches a maximum value at the concentration of 0.05M, and the electron affinity is consistent. As the thickness of the film increases, the photocurrent increases with a maximum value at the thickness of 4600$\AA$, and electron affinity does not change.