• Proceedings of the KSME Conference
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• 2001.11b
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• pp.124-130
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• 2001

The heat transfer and flow measurements were made on a cylindrical pedestal mounted on a flat plate with a turbulent impinging air jet. The heat transfer coefficient distributions on the flat plate were measured using the shroud-transient technique and liquid crystal was used to measure the surface temperature. The jet Reynolds number (Re) is 23,000, the dimensionless nozzle-to-surface distance (L/d) from 2 to 10, the dimensionless pedestal diameter-to-height (H/D) from 0 to 1.5, the dimensionless 2nd pedestal diameter-to-height ($H/D_2$) from 0 to 0.4 and the distance from the stagnation point to 2nd pedestal (p/D). The results show that for H/D = 0.5 to 1.5, the Nusselt number distributions on the plate surface exhibit a maximum between $r/d\;{\cong}\;1.0$ and 1.5. The presence of the pedestal appears to cause the flow separation and reattachment on the plate surface, which results in the maximum heal transfer coefficient. Also, for p/D = 2.5 and $H/D_2$ = 0.3, the local Nusselt number in the region corresponding to $r/d\;{\cong}\;1.1$ was increased up to 50% compared to that for $H/D_2=0$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.6
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• pp.51-58
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• 2006

The spray characteristics of liquid jet injected into subsonic cross-flow were investigated experimentally. Spray trajectories were captured using CCD camera. Droplet sizes were measured using PDPA and Image Express. The nozzle diameter was 0.5 mm, and its length-to-diameter ratios (L/D) ran$4.11{\times}10^6$ged from 1.0 to 6.0. Experimental results indicate that the breakup point is delayed by increasing gas momentum ratio and the penetration length is decreased by increasing Weber number. At low injection angle(${\theta}$ < $90^{\circ}$), Weber number is dominant parameter for trajectories, but at high injection angle(${\theta}$ > $90^{\circ}$), L/D is dominant parameter for trajectories rather than Weber number.

• Journal of Power System Engineering
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• v.14 no.3
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• pp.5-12
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• 2010

The purpose of this study is to analyze heterogeneous distribution of branch-like structure at downstream region of inner spray. The previous many studies about diesel spray structure have yet stayed in the analysis of 2-D structure, and there are very few of informations which are concerned with 3-D analysis of the structure. The heterogeneous distribution of droplets in inner spray affects the mixture formation of diesel spray, and also the combustion characteristics of the diesel engines. Therefore, in order to investigate 3-D structure of evaporative spray the laser beam of 2-D plane was used in this study. Liquid fuel was injected from a single-hole nozzle (l/d=5) into a constant-volume vessel under high pressure and temperature in order to visualize the spray phenomena. The incident laser beam was offset on the central axis. From the images analysis taken by offset of laser beam, we examine formation mechanism of heterogeneous distribution by vortex flow at the downstream of the diesel spray. As the experimental results, the branch-like structure formed heterogeneous distribution of the droplets consists of high concentration of vapor phase in the periphery of droplets and spray tip of branch-like structure. Also the 3-D spatial structure of the evaporative diesel spray can be verified by images obtained from 2-D measurement methods.

• Membrane and Water Treatment
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• v.14 no.3
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• pp.129-140
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• 2023

The appropriate injection of H₂O₂ is essential to produce hydroxyl radicals (OH·) by mixing H₂O₂ quickly and exposing the resulting H₂O₂ solution to UV irradiation. This study focused on evaluating mixing device of H₂O₂ as a design factor of UV/H₂O₂ AOP pilot plant using a surface water. The experimental investigation involved both experimental and model-based analyses to evaluate the mixing effect of different devices available for the H₂O₂ injection of a tubular hollow pipe, elliptical type of inline mixer, and nozzle-type injection mixer. Computational fluid dynamics analysis was employed to model and simulate the mixing devices. The results showed that the elliptical type of inline mixer showed the highest uniformity of 95%, followed by the nozzle mixer with 83%, and the hollow pipe with only 18%, after passing through each mixing device. These results indicated that the elliptical type of inline mixer was the most effective in mixing H₂O₂ in a bulk. Regarding the pressure drops between the inlet and outlet of pipe, the elliptical-type inline mixer exhibited the highest pressure drop of 15.8 kPa, which was unfavorable for operation. On the other hand, the nozzle mixer and hollow pipe showed similar pressure drops of 0.4 kPa and 0.3 kPa, respectively. Experimental study showed that the elliptical type of inline and nozzle-type injection mixers worked well for low concentration (less than 5mg/L) of H₂O₂ injection within 10% of the input value, indicating that both mixers were appropriate for required H₂O₂ concentration and mixing intensity of UV/ H₂O₂ AOP process. Additionally, the elliptical-type inline mixer proved to be more stable than the nozzle-type injection mixer when dealing with highly concentrated pollutants entering the UV/H₂O₂ AOP process. It is recommended to use a suitable mixing device to meet the desired range of H₂O₂ concentration in AOP process.

• Journal of Power System Engineering
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• v.10 no.3
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• pp.32-37
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• 2006

In this paper, we present the flow and heat transfer characteristics with the array of impinging jet nozzles by using the numerical computation and experiment. Numerical solutions were obtained for dimensionless gap H=6, dimensionless outlet length L=10 and Reynolds number Re=1500 by using the commercial CFD code, CFX-5. Experimental and numerical results were agreed well with each other. It was found that the impinging jet with circular array nozzles generated the uniform heat transfer area and the maximum heat transfer is higher than rectangular array nozzles for certain parameter sets. It is one of the most important utilities providing steam to turbine in order to supply mechanical energy in thermal power plant. It is composed of thousands of tubes for high efficient heat transfer.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.75-80
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• 2005

The present work was undertaken to numerically analyze the defrosting phenomena of windshield glass. In order to analysis the phase change from frost to water on windshield glass by discharging hot air from a defroster nozzle, the flow and the temperature field of the cabin interior, the heat transfer through the windshield glass, and the phase change of frost should be solve simultaneously. In the present work, the flow field was obtained by solving 3-D incompressible Navier-Stokes equations, and the temperature field was computed from the incompressible energy equation. The phase change process was solved by the enthalpy method. For the code validation, the temperature and the phase change of the driven cavity were calculated. The calculation showed a good agreement with other numerical results. Then, the present code was applied to the defrosting problem of a real automobile, and a good agreement with the experimental data was also obtained.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.726-731
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• 2000

This study was experimentally analyzed to improve the performance and to reduce exhaust emissions in a turbochaged D.I. diesel engine of the displacement 9.4L. In generally, the system of intake port, fuel injection and turbocharger are very important factors which have influence on the engine performance and exhaust emission because the properties in the injected fuel depend on the combustion characteristics. The optimum results which is tested as available factors fur better performance and emission are as follows; the swirl ratio is 2.43, compression ratio is 16, combustion bowl is $5^{\circ}$ re-entrant type, nozzle hole diameter is ${\phi}0.28*6$, injection timing is BTDC $13^{\circ}CA$ and turbocharger is GT40 model which are selected compressor A/R 0.58 and turbine A/R 1.19.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.165-168
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• 2000

로켓엔진에서 노즐은 추력을 발생하고, 단위 면적당 열 전달이 최대가 되는 곳으로 구조적으로 가장 취약한 부분이다. 이런 가혹한 조건에서 사용되어질 수 있는 4D 탄소/탄소 복합재를 제조하였으며. 초밀도화시, 탄화압력은 100bar 와 900bar 에서 각각 시행되었다. 만들어진 시편의 밀도는 1.5~l.9g/$cm^3$ 이었다. 실제 로켓을 모사할 수 있는 지상연소시험을 통해 밀도에 따른 삭마율을 계산한 결과, 밀도가 높을수록 삭마율은 감소하였다. 또한 3-point bending test를 통해 굽힘강도(flexural strength)를 측정하였으며, 굽힘강도를 개선시켜주었다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.155-158
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• 2005

The spray characteristics of liquid jet minted in subsonic cross-flow were investigated numerically and experimentally. The behaviors of column, penetration and breakup of plain liquid jet in non-swirling cross-flow of air have been studied. Numerical and physical models are based on a modified KIVAII code. The primary atomization is represented by a wave model based on the KH(Kelvin-Helmholtz) instability that is generated by a high interface relative velocity between the liquid and gas flows. CCD camera has been utilized in oder to capture the spray trajectory. The nozzle diameter was 0.5 mm and its L/D ratios were between 1 and 5. Numerical and experimental results indicate that the breakup point is delayed by increasing gas momentum ratio, the penetration decreases by increasing Weber number and the turbulent or nonturbulent liquid jet is obtained at different L/D ratio.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.3
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• pp.324-333
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• 1998

Measurements of the local heat transfer coefficients on a hemispherically concave surface with a round oblique impinging jet were made. The liquid crystal transient method was used for these measurements. This method, which is a variation of the transient method, suddenly exposes a preheated wall to an impinging jet while video recording the response of liquid crystal for the surface temperature measurements. The Reynolds number used was 23,000 and the nozzle -to -jet distance was L/d=2, 4, 6, 8 and 10 and the jet angle was $\alpha$=0$^{\circ}$, 15$^{\circ}$, 30$^{\circ}$and 40$^{\circ}$. In the experiment, the maximum Nusselt number at all region occurred at L/d(equation omitted)6 and Nusselt number decreases as the inclined jet angle increases. For the normal jet the contours of constant Nusselt number are circular and as the jet is inclined closer and closer to the surface the contours become elliptical shape. The decreasing rate of the Nusselt number at X/d＞ 0(upstream) on a surface curvature are higher than those on a flate plate and the decreasing rate of the Nusselt number at X/d ＜0(downstream) on a surface curvature are lower than those on a flate plate. And also, the decreasing rate of local Nusselt number distribution at X/d ＜0(upstream) exhibit lower than with X/d ＜0(downstream) as jet angle increases. The second maximum Nusselt number occurred at long distance from stagnation point as jet angle increases.