• 한국연소학회:학술대회논문집
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• 2001.06a
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• pp.9-16
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• 2001

When large size nozzle with low jet velocity is used, the buoyancy effect arises from the density difference among propane, air, and burnt gas. Flame characteristics in such buoyant jets have been investigated numerically to elucidate the effect of buoyancy on lifted flames. It has been demonstrated that the cold jet has circular cone shape since upwardly injected propane jet decelerates and forms stagnation region. In contrast to the cold flow, the reacting flow with a lifted flame has no stagnation region by the buoyancy force induced from the burnt gas. To further illustrate the buoyancy effect on lifted flames, the reacting flow with buoyancy is compared with non-buoyant reacting flow. Non-buoyant flame is stabilized at much lower height than the buoyant flame. At a certain range of fuel jet velocities and fuel dilutions. an oscillating flame is demonstrated numerically showing that the height of flame base and tip vary during one cycle of oscillation. Under the same condition. non-buoyant flame exhibits only steady lifted flames. This confirms the buoyancy effect on the mechanism of lifted flame oscillation.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.55.2-55.2
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• 2010

기존의 thermal spray coating은 분사시 가스와 입자가 높은 열을 동반하여 상대적으로 차가운 기판과의 충돌되는 과정에서 기판과 입자 사이에 열응력이 발생하게 되고, 이것은 코팅 특성을 저하시킨다. 또한 고온의 가연성 가스등의 사용으로 작업 시 안전문제 등의 단점이 있었다. 이러한 단점을 보완하기 위하여 분사 시 운동에너지를 주로 이용하는 cold spray coating 공정이 개발되었다. 이 공정은 코팅 입자를 임계속도 이상으로 가속시켜 입자와 기판이 충돌시 소성 변형을 통해 적층되는 코팅기술이다. Cold spray coating공정은 상온 코팅이 가능하기 때문에 주입입자의 물성이 비교적 그대로 유지되고, 고온의 열로 인한 기판의 변질을 막을 수 있다. Cold Spray coating에서 주로 원형 노즐을 사용하나 본 연구에서는 분사 효율 향상을 위한 광폭노즐을 사용하여 코팅 시간 단축을 기대하고 있다. 임계속도 이상의 입자 확보를 위하여 노즐의 expansion ratio와 노즐 shape의 변화를 주어 그에 따른 노즐내의 유동장을 수치해석을 통해 계산하였다. 분사되는 출구면과 기판 사이의 입자 속도 분포를 해석하였고, 이를 통해 임계속도 이상의 속도를 갖는 유효 입자들의 분포 및 유효 분사 면적을 예측하였다. 또한, 기존의 원형 노즐과 광폭 노즐과의 유동장 비교 및 각 노즐 분사면을 분석하여 cold spray coating공정에서의 효율적인 노즐 형상을 디자인하였다.

• Journal of Bio-Environment Control
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• v.6 no.3
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• pp.183-189
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• 1997

This study was performed to Investigate size of droplet sprinkled from mini-sprinkler. Twelve different kinds of the sprinkler having various structures and sizes of nozzle orifices were selected and tested. Diameters of the droplet reached at several distances from a sprinkler were measured by a machine vision system and the volume median diameters (VMM) were determined statistically. The size of droplet was not affected much by the size of nozzle orifice of a sprinkler but was rather more affected by structure of the sprinkler, especially by the shape of spreader of the sprinkler. Experiment of varying pressure of sprinkling water validated that the size of droplet was inversely proportional to water pressure powered by 1/3. Hence the size of droplet at any water pressure could be easily estimated from experimental data. The size of droplet increased as travel distance of the droplet increases in a relationship of and order function. The size of droplet of the tested sprinkler were in the ranges of 100-300fm within 1m of droplet travel distance, 230~470${\mu}{\textrm}{m}$ within 1~2m of droplet travel distance and 300~770${\mu}{\textrm}{m}$ within 2~3m of droplet travel distance.

• Clean Technology
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• v.29 no.4
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• pp.305-312
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• 2023

Due to the strengthening of environmental requirements, aging denitrification facilities need to improve their performance. The present study aims to suggest the possibility of improving performance using computational analysis techniques. This involved modifying both the geometric design and the operating conditions, including the flow path shape of the equipment such as the inlet guide vane and the curved diffusing part, and the flow control of the ammonia injection nozzle. The conditions presented in this study were compared with existing operating conditions in terms of the flow uniformity, the NH₃/NO molar ratio of the mixed gas flowing into the catalyst layer, and the total pressure drop of the facility. The flow field applied in the computational analysis ranged from the outlet of the economizer in the combustion furnace to the inlet of the air preheater, the full domain of the denitrification facility. The performances were derived by solving the flow fields using ANSYS-Fluent and the injection amount of ammonia was adjusted for each nozzle using Design Xplorer. Compared to the denitrification performances of the equipment currently in operation, the conditions proposed in this study showed an improvement in the flow uniformity and NH₃/NO composition ratio by 45.1% and 8.7%, respectively, but the total pressure drop increased by 1.24%.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.7
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• pp.675-682
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• 2013

To verify the effect of inner- and outer-stage gas jets, a shear coaxial injector was designed to analyze the axial velocity profile and breakup phenomenon with an increase in the measurement distance. When the measurement position was increased to Z/d=100, the axial flow showed a fully developed shape due to the momentum transfer, aerodynamic drag effect, and viscous mixing. An inner gas injection, which induces a higher momentum flux ratio near the nozzle, produces the greater shear force on atomization than an outer gas injection. Inner- and Outer-stage gas injection do not affect the mixing between the inner and outer gas flow below Z/d=5. The experiment results showed that the main effect of liquid jet breakup was governed by the gas jet of an inner stage. As the nozzle exit of the outer-stage was located far from the liquid column, shear force and turbulence breaking up of the liquid jets do not fully affect the liquid column. In the case of an inner-stage gas injection momentum flux ratio within 0.84, with the increase in the outer gas momentum flux ratio, the SMD decreases. However, at an inner-stage gas jet momentum flux ratio over 1.38, the SMD shows the similar distribution.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.34 no.1
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• pp.1-10
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• 2022

In this study, the two horizontal shroud tidal current energy converter, which can generate power even under low flow speed conditions, was developed. In order to determine the shape of the shroud system, a three-dimensional numerical simulation test was conducted, and a 1/6 scale down model was made to perform a hydraulic model experiment. The hydraulic model experiment was performed under four flow conditions, and the flow speed, torque, and RPM were measured for each experimental case. As a result of the numerical simulation test, it was found that the flow speeds passing through the nozzle were increased by about 2~3 times in the cylinder, and when the extension ratio was 2:1, the highest flow speed was shown. In addition, it was found that the flow speeds increased 2.8 times when the diameter ratio between the nozzle and the cylinder was 1.5:1. Meanwhile, as a result of the hydraulic model experiment, it was found that when the tip speed ratio was between 1.75 and 2, the power coefficient was 0.32 to 0.34.

• Journal of the Korean Vacuum Society
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• v.22 no.1
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• pp.1-6
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• 2013

In this paper, to develop linear source for evaporating $600{\times}1,200mm$ size of large area CIGS absorber layer, we simulated linear thermal source and obtained ${\pm}5%$ thickness uniformity with various nozzle sizes and regular nozzle distance. Flux density was confirmed linear source length. Using this linear source, we tested thickness uniformity of Copper, Indium single layer which was obtained Cu ${\pm}5%$ and In ${\pm}5%$ thickness uniformity. And then CIGS absorber layers were evaporated with In-line single-stage co-evaporation. Large area CIGS absorber layers were confirmed composition uniformity of $$Cu{\leq_-}5%$$, $$In{\leq_-}7%$$, $$Ga{\leq_-}4%$$, $$Se{\leq_-}3%$$ with 600 mm width by XRF. Uniform shape of CIGS absorber layers was confirmed by SEM. XRD showed peaks which indicate chalcopyrite structure of CIGS absorber layers. Thus, developed linear source is suitable for evaporating CIGS absorber layer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.9
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• pp.1317-1324
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• 1998

In general, DI gasoline engine has the advantages of higher power output, higher thermal efficiency, higher EGR tolerance and lower emissions due to the operation characteristics of increased volumetric efficiency, compression ratio and ultra-lean combustion scheme. In order to apply the concept of stratified charge into direct injection gasoline engine, some kinds of methodologies have been adapted in various papers. In this study, a reflector was adapted around the injector nozzle to apply the concept of stratified charge combustion which leads the air-fuel mixture to be rich near spark plug. Therefore, the mixture near the spark plug is locally rich to ignite while the lean mixture is wholly introduced into the combustion chamber. The characteristics of combustion is analyzed with the variations of fuel injection pressure and load in a stratified -charge direct injection single cylinder gasoline engine. The obtained results are summarized as follows ; 1. The MBT spark timing approached to TDC with the increase of load on account of the increase of evaporation energy, but has little relation with fuel injection pressure. 2. The stratification effects are apparent with the increase of injection pressure. It is considered by the development of secondary diffusive combustion and the increase of heat release of same region, but proceed rapidly than diesel engine. Especially, in the case of high pressure injection (l70bar) and high load (3.0kgf m), the diffusive combustion parts are developed excessively and results in the decrease of peak pressure than in the case of middle load. 3. The index of engine stability, COVimep value, is drastically decreased with the increase of load. 4. To get better performance of DI gasoline engine development, staged optimizaion must be needed such as injection pressure, reflector, intake swirl, injection timing, chamber shape, ignition system and so on. In this study, the I50bar injection pressure is appeared as the optimum.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1391-1398
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• 2011

Design and performance analysis of a steam turbine for variations of degree of reaction were performed by computer simulation. Design parameters such as blade angles, exit areas, and heights of the nozzle and moving blade were represented as functions of the degree of reaction. The main performance factors such as turbine power, diagram efficiency, and axial thrust were also expressed in terms of the degree of reaction. For further information about the design and performance, the blade angles and main performance factors were investigated as functions of the flow coefficient. The turbine power and diagram efficiency reached a maximum value for a given degree of reaction and flow coefficient, and the symmetric shape of the moving blade showed distortion as the degree of reaction was increased.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.1
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• pp.105-113
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• 2009

The performance of a direct-injection type diesel engine often depends on the strength of swirl or squish, shape of combustion chamber, the number of nozzle holes, etc. This is of course because the combustion in the cylinder was affected by the mixture formation process. In this paper, combustion process of biodiesel fuel was studied by employing the piston which has several grooves with inclined plane on the piston crown to generate swirl during the compression stroke in the cylinder in order to improve the atomization of high viscosity fuel such as biodiesel fuel and toroidal type piston generally used in high speed diesel engine. To take a photograph of flame, single cylinder, four stroke diesel engine was remodeled into two stroke visible engine and high speed video camera was used. The results obtained are summarized as follows; (1) In the case of toroidal piston, when biodiesel fuel was supplied to plunger type injection system which has very low injection pressure as compared with common-rail injection system, the flame propagation speed was slowed and the maximum combustion pressure became lower. These phenomena became further aggravated as the fuel viscosity gets higher. (2) In the case of swirl groove piston, early stage of combustion such as rapid ignition timing and flame propagation was activated by intensifying the air flow in the cylinder. (3) Combustion process of biodiesel fuel was improved by the reason mentioned in paragraph (2) above. Consequently, the swirl grooves would also function to improve the combustion of high viscosity fuel.