• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1534-1539
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• 2004

This experiment has been carried out to measure the process of droplet formation between water phase fluid(PVA 3%) and organic phase fluid(oil) and vector fields measured by a Dynamic Micro-PIV method in the inside of a droplet while generated. Droplet length controlled by changing flow rate conditions in microchannel. Water-in-oil(W/O) droplets successfully generated at a Y junction and cross microchannel. But oil-in-water(O/W) droplets could not be formed at a Y junction microchannel. That is, PVA 3% flow could not be detached from the PDMS surface and ran parallel with oil flow. When PVA 3% flow rate was constant, droplet length and time period decreased as oil flow rate increased, but droplet frequency increased. When PVA 3% and oil flow rate ratio was constant, droplet length and time period decreased as flow rate increased, but droplet frequency increased. All that case, Standard deviation of droplet formation have less than 5% at averaged droplet length and regular-sized droplets were reproducibly formed.

• 대한기계학회논문집B
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• 제26권10호
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• pp.1355-1363
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• 2002

An experimental study was conducted to investigate the interaction phenomena of droplet array combustion in ambient environment. The droplet with 1 mm in diameter was supported from an optical fiber and ignited with a hot wire. Combustion lifetimes and burning rate constants were measured for fuel of nheptane according to parameters, which were junction and suspender spacings, and array configuration. Results show that the burning process considerably depends on the initial away configuration. The d$^2$-law is found to be correct when applied to both of the droplets in away and the single droplet. For separation distance of about 5mm, there exists a critical state. So the transition from a merged flame to separated flames occurs and burning velocity is much faster than before. Combustion lifetime of the lower droplet is shorter than that of the upper droplet in the two-dimensional arrays combustion. Burning rate constants of the droplets in arrays are smaller than that of the single droplet, while they become higher as separation distance increases. Combustion lifetimes of the droplets in arrays are longer than that of the single droplet and decrease as separation distance increase. It is concluded that the array configuration and the mergedness of the flame are the most important factors governing multi-droplet combustion.

• 대한기계학회논문집B
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• 제23권6호
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• pp.778-787
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• 1999

In this study, the autoignition process of liquid fuel, injected into hot and stagnant air in a 2-D axisymmetric confined cylindrical combustor, has been investigated. Eulerian-Lagrangian scheme was adopted to analyze the two-phase flow and combustion. The unsteady conservation equations were used to solve the transition of the gas field. Interactions between two phases were accounted by using the particle source in cell (PSI-Cell) model, which was used for detailed consideration of the finite rates of transports between phases. And infinite conduction model was adopted for the vaporization of droplets. The results have shown that the process of the autoignition consists of heating up of droplets, vaporization, mixing and ignition. The ignition criteria could be determined by the temporal variations of temperature, reaction rate and species mass fraction. And the effects of various parameters on ignition phenomena are examined. These have shown that the increasing the reaction rate and/or the vaporization rate can reduce the ignition delay time.

• 한국가시화정보학회지
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• 제5권2호
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• pp.39-47
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• 2007

This paper describes an experimental study on the droplet formation and the subsequent motion in a microchannel having a cross junction. While one kind of liquid (pure water or water-surfactant mixture) is drawn into a horizontal inlet channel, the other kind (oil) is introduced through two vertical inlet channels. Due to the effect of surface tension on the interface between the two fluids, the droplets of the first fluid are formed near the cross junction. In this study, we have found that the droplet formation is affected even by slight difference in the surface tension. When the surface tension between two fluids is decreased, the droplet size is decreased in order to keep the equilibration between the pressure and the surface tension. In addition, the time interval between each of the droplet formations is decreased and the distance between droplets is also decreased when the surface tension is decreased.

• 대한기계학회논문집B
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• 제30권5호
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• pp.489-495
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• 2006

Proton exchange membrane (PEM) should be sufficiently hydrated with a careful consideration of heat and water management. Water management has been a critical operation issue for better understanding the operation and optimizing the performance of a PEM fuel cell. The flooding on cathode side resulting from excess water can limit the fuel cell performance. In this study, the visual cell was designed and fabricated fur the visualization of liquid water droplet dynamics related to cathode flooding in flow channels. The experiment was carried out to observe the formation, growth and removal of water droplets using CCD imaging system. Effects of operating conditions such as cell temperature, air flow rate and air relative humidity on cathode flooding characteristics were mainly investigated. Based on this study, we can get the basic insight into flooding phenomena and its two-phase flow nature. It is expected that data obtained can be effectively used fur the setup and validation of two-phase PEM fuel cell models considering cathode flooding.

• 한국산학기술학회논문지
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• 제13권9호
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• pp.4334-4340
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• 2012

본 연구에서는 미세 액적을 발생시키는 액적 발생 장치를 개발 제작하고 이에 대한 성능 평가를 실시하였다. 액적 발생 장치는 spray-evaporation method를 기초로 제작하였으며, 0.3mm, 0.5mm의 오리피스를 사용하였다. 압축 공기 공급 압력을 1bar에서 4bar로 증가시키면서 공급 압력에 따른 발생되는 액적 크기의 미세 정도를 비교하였다. 또한 SMPS(Scanning Mobility Particle Sizer)와 OPC(Optical Particle Counter)를 이용하여 서로 다른 오리피스를 장착한 액적 발생 장치에서 발생되는 액적의 크기 분포를 측정하였다. 연구 결과, 0.3mm 오리피스를 장착한 장치에서 발생되는 액적은 $0.3{\mu}m$ 인근의 크기가 가장 많았으며, 미립화되는 입자는 매우 안정적이었다. 또한 0.5mm 오리피스를 장착한 장치가 0.3mm 오리피스를 장착한 장치에 비해 발생되는 액적의 크기가 큰 것으로 나타났다. 이러한 액적 발생 장치는 입자의 미세한 응집 현상이 나타나는데, 이것은 내부 액체가 미세한 액적으로 미립화되어 분사되기 때문인 것으로 사료된다. 본 연구에서 제작한 액적 발생 장치는 미세 입자를 미립화하기 위한 에어로졸 발생 장치로 사용 가능한 것으로 판단된다.

• Asian Journal of Atmospheric Environment
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• 제8권4호
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• pp.175-183
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• 2014

To visually and chemically verify the rainout of soot particles, a model experiment was carried out with the cylindrical chamber (0.2 m (D) and 4 m (H)) installing a cloud drop generator, a hydrotherometer, a particle counter, a drop collector, a diffusing drier, and an artificial soot particle distributer. The processes of the model experiment were as follows; generating artificial cloud droplets (major drop size : $12-14{\mu}m$) until supersaturation reach at 0.52%-nebulizing of soot particles (JIS Z 8901) with an average size of $0.5{\mu}m$-counting cloud condensation nuclei (CCN) particles and droplets by OPC and the fixation method (Ma et al., 2011; Carter and Hasegawa, 1975), respectively - collecting of individual cloud drops - observation of individual cloud drops by SEM - chemical identifying of residual particle in each individual droplet by SEM-EDX. After 10 minutes of the completion of soot particle inject, the number concentrations of PM of all sizes (> $0.3{\mu}m$) dramatically decreased. The time required to return to the initial conditions, i.e., the time needed to CCN activation for the fed soot particles was about 40 minutes for the PM sized from $0.3-2.0{\mu}m$. The EDX spectra of residual particles left at the center of individual droplet after evaporation suggest that the soot particles seeded into our experimental chamber obviously acted as CCN. The coexistence of soot and mineral particle in single droplet was probably due to the coalescence of droplets (i.e., two droplets embodying different particles (in here, soot and background mineral particles) were coalesced) or the particle capture by a droplet in our CCN chamber.

• 한국세라믹학회지
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• 제35권11호
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• pp.1171-1181
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• 1998

$SrZr_{0.95}$$Y_{0.05}$$O_{2.975}$ powder was synthesized by ultrasonic spray pyrolysis using a solution that Sr carbonate and Zr and Y nitrates were dissolved in a citric acid solution. The processes of particle formation were in-vestigated with respect to solution properties and pyrolysis temperature. With changing the solution con-centration form 0.1M to 0.01M there was a tendency that average sizes of droplets and particles were de-creased and their size distributions were narrowed. Citrate functional groups converted the droplets into gel particles which prevented an inhomogeneous precipitation of the metal ions and facilitated the diffusion of gases during thermal decomposition. As a result the powder having spherical particles without hollow par-ticles could be prepared. Low pyrolysis temperature led to amorphous particles due to incomplete pyrolysis and made the particles difficult to maintain spherical shape due to retarded gelation of the droplets. Whereas higher pyrolysis temperature produced hollow and broken particles because the droplets un-derwent rapid gelationand decomposition. The particles obtained at two pyrolysis temperature $500^{\circ}$and $1000^{\circ}C$ consisted of a perovskite phase and a very small amount of $SrCO_3$ However after calcination at $1000^{\circ}C$ the particles contained a single perovskite phase having an average particle size of 0.63${\mu}{\textrm}{m}$ and an apparent density near to the theoretical density.

• 한국분무공학회지
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• 제25권4호
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• pp.162-169
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• 2020

The worldwide focus on reducing the emissions, fuel and lubricant consumption in T-GDI engines is leading engineers to consider the crankcase ventilation and oil mist separation system as an important means of control. In today's passenger cars, the oil mist separation systems mainly use the inertia effect (e.g. labyrinth, cyclone etc.). Therefore, this study has investigated high efficiency cylinder head-integrated oil-mist separator by using a compact multi-impactor type oil mist separator system to ensure adequate oil mist separation performance. For this purpose, engine dynamometer testing with oil particle efficiency measurement equipment and 3D two-phase flow simulation have been performed for various engine operating conditions. Tests with an actual engine on a dynamometer showed oil aerosol particle size distributions varied depending on operating conditions. For instance, high rpm and load increases bot only blow-by gases but the amount of small size oil droplets. Submicron-sized particles (less than 0.5 ㎛) were also observed. It is also found that the impactor type separator is able to separate nearly no droplets of diameter lower than 3 ㎛. CFD results showed that the complex aerodynamics processes that lead to strong impingement and break-up can strip out large droplets and generate more small size droplets.

• 한국입자에어로졸학회지
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• 제13권3호
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• pp.119-125
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• 2017

A novel two stage cylindrical cyclone was developed for a 3 phase separator in shale oil production industry. The cyclone performance was compared with a cone type cyclone and multi cyclone at the same experimental condition using water and oil mists generated by a humidifier and atomizer at the flow rate 1 to $2m^3/min$. The removal efficiency of total suspended water droplets by the novel cyclone, calculated using inlet and outlet concentrations measured by an optical particle counter, was 99% which is higher than 90% of oil droplet removal efficiency at $2m^3/min$. It might be due to the evaporation of small water droplets during the tests. The water and oil droplet removal performance of the novel cyclone based on the quality factor which is a function of pressure drop and removal efficiency was the highest among three cyclones. The results indicate that the cyclone could be an economical device to remove water and oil mists from shale gas generation processes where a huge three phase separator is commonly used.