• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1522-1527
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• 2004

The purpose of this study is to investigate the effect of swirler angle and swirl chamber aspect ration of nozzle on the characteristics of single and twin spray. The performances of nozzle has been investigated by measurements of spray angle, droplet size, velocity and Weber number at a water pressure 0.4MHz. Visualization of spray was conducted to obtain the spray angle and breakup process. The spray characteristics such as droplet size and velocity were measured by Phase Doppler Anemometry(PDA). It was found that the smaller swirler angle, the larger axial velocity became. It was also shown that the larger aspect ratio, the smaller droplet diameter became.

• International Journal of Automotive Technology
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• 제6권2호
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• pp.87-93
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• 2005

Spray patterns were visualized using the shadowgraph method, and the droplet size and velocity were measured using PDPA for high-pressure injections up to 2,600 bars. The spray pattern and spray characteristics, such as penetration, spray width, spray angle, droplet size, injection duration, and droplet velocity, were investigated to determine the suitable injection pressure. Spray penetration, width, angle, and velocity increased continuously up to 2,600 bars with the injection pressure in a high-pressure region. The rate of improvement of the above spray characteristics, however, declined rapidly, when the injection pressure reached 2,000 bars. The injection duration and droplet size generally decreased with the increase in the injection pressure, while the rate of improvement decreased abruptly after 2,000 bars. Consequently, the improvement rate of the spray characteristics became blunt at over 2,000 bars. This means that the suitable injection pressure is around 2,000 bars.

• Journal of Industrial and Engineering Chemistry
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• 제67권
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• pp.123-131
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• 2018

Using mixed nonionic surfactants Span/Tween, we investigated the effects of HLB value on the O/W emulsion stability and rheological behaviors. In this study, MS-01 (Span 60 & Tween 60) and MS-02 (Span 80 & Tween 80) was used as mixed nonionic surfactants. We considered required HLB value 10.85 and selected corresponding HLB value range 8-13. The droplet size distributions, droplet morphology, rheological properties, zeta-potential and creaming index of the emulsion samples were obtained to understand the mechanism and interaction of droplets in O/W emulsion. The results indicated that optimal HLB number for O/W emulsions was 10.8 and 10.7, while using MS-01 surfactant and MS-02 surfactant respectively. MS-01 (HLB = 10.8) sample and MS-02 (HLB = 10.7) sample showed smallest droplet size and highest zeta-potential value. Rheological properties are measured to understand rheological behaviors of emulsion samples. All emulsion samples showed no phase separation until 30 days storage time at $25^{\circ}C$.

• 한국응용과학기술학회지
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• 제30권4호
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• pp.602-611
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• 2013

We have investigated the influence of system composition and preparation conditions on the particle size of vitamin E acetate (VE)-loaded nanoemulsions prepared by PIC(phase inversion composition) emulsification. This method relies on the formation of very fine oil droplets when water is added to oil/surfactant mixture. The oil-to-emulsion ratio content was kept constant (5 wt.%) while the surfactant-to-oil ratio (%SOR) was varied from 50 to 200 %. Oil phase composition (vitamin E to medium chain ester ratio, %VOR) had an effect on particle size, with the smallest droplets being formed below 60 % of VOR. Food-grade non-ionic surfactants (Tween 80 and Span 80) were used as an emulsifier. The effect of f on the droplet size distribution has been studied. In our system, the droplet volume fraction, given by the oil volume fraction plus the surfactant volume fraction, was varied from 0.1 to 0.3. The droplet diameter remains less than 350 nm when O/S is fixed at 1:1. The droplet size increases gradually as the increasing the volume fraction. Particle size could also be reduced by increasing the temperature when water was added to oil/surfactant mixture. By optimizing system composition and homogenization conditions we were able to form VE-loaded nanoemulsions with small mean droplet diameters (d < 50 nm). The PIC emulsification method therefore has great potential for forming nanoemulsion-based delivery systems for food, personal care, and pharmaceutical applications.

• 대한기계학회논문집
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• 제17권7호
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• pp.1823-1832
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• 1993

CWS(coal-water slurry) is used for application in power plants, boilers, industrial furnaces. A single coal-water slurry droplet ignition has been examined to reveal the basic nature of their evaporation, volatilization and heating processes. The interior droplet temperature distribution has been considered. The effect of coal thermal conductivity, droplet size, water fraction in the slurry, gas temperature and velocity and radiation on the ignition phenomena were also studied. Either increasing the velocity and gas temperature or decreasing the droplet size and water fraction in the slurry may reduce the time for evaporation and ignition delay time.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1752-1757
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• 2008

Simple and highly efficient droplet merging method is proposed, which enables two nanoliter or picoliter droplets to merge regularly in a straight microchannel. We observe that two droplets of the same size but of different viscosities are merged by velocity difference induced as they are transported with the carrier fluid. To make viscosity difference, the mass ratio of water and glycerol is varied. Two droplets of the same size or of different sizes are generated alternatingly in the cross channel by controlling flowrates. This droplet merging method can be used to mix or encapsulate one target sample with another material, so that it can be applied to cell lysis, particle synthesis, drug discovery, hydrogel-bead production, and so on.

• 대한기계학회논문집
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• 제18권4호
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• pp.1039-1049
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• 1994

The intermitternt and transient fuel spray have been investigated from the simultaneous measurement of droplet sizes and velocities by using Phase/Doppler Particle Analyzer(PDPA). Measurement have been done on the spray axis and at the edge of the spray near nozzle at various gas-to-liquid density ratios(.rho./sub g//.rho./sub l/) that ranges from those found in free atmospheric jets to conditions typical of diesel engines. Probability density distributions of the droplet size and velocity were obtained from raw data and mathematical probability density functions which can fit the experimental distribations were extracted using the principle of maximum likelihood. In the near nozzle region on the spray axis, droplet sizes ranged from the lower limit of the measurement system to the order of nozzle diameter for all (.rho./sub g/ /.rho./sub l/) and droplet sizes tended to be small on the spray edge. At the edge of spray, average droplet velocity peaked during needle opening and needle closing. The rms intensity is greatly incresed as the radial distance from the nozzle is increased. The probability density function which can best fit the physical breakage process such as breakup of fuel drops is exponecially decreasing log-hypebolic function with 4 parameters.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.559-564
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• 2008

A prediction of binary droplets collision is important in the formation of falling drops and the evolution of sprays. The droplet velocity, impact parameter and drop-size ratio have influence on the interaction of the droplets. By the effect of these parameter, the collision processes are generated with the complicated phenomena. The droplet collision can be classified into four interactions such as the bouncing, coalescence, reflexive separation and stretching separation. In this study, the two-phase flow of the droplet collision was simulated numerically by using the Level Set method. 2D axi-symmetric simulations on the head-on collisions in the coalescence and reflexive separation, and 3D simulation on the off-center collisions in the coalescence and stretching separation were performed. These numerical results showed good agreements with the experimental and analytical results. For tracking the identity of droplets after the collision, transport equation for the volume fraction of the each initial droplet were used. From this, the identities of droplets were analyzed on the collision of droplets having different size.

• Journal of Advanced Marine Engineering and Technology
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• 제37권1호
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• pp.1-8
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• 2013

데칸에 물을 혼합하여 일정한 크기와 간격으로 액적을 형성하여 물과의 혼합비율, 분위기 온도, 액적의 크기와 간격 등이 유화액적의 점화와 미소폭발의 특성에 어떠한 영향을 주는가를 고온의 연소실에서 특성을 비교하였다. 점화가 시작하는 온도는 물의 비율이 낮을수록, 액적 크기가 클수록 낮아진다. 물의 혼합비율에 따른 수명시간은 단일 액적에서는 미소폭발의 영향으로 수명시간이 현저하게 짧아지나, 액적크기가 크고 분위기온도가 높을수록 미소폭발의 발생빈도는 자주 나타나게 된다. 퍼짐시간은 물의 혼합비율이 적을수록 더 빨라지고 서스펜더의 수가 많을수록 더 짧아짐을 알 수 있다.

• 대한기계학회논문집A
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• 제29권3호
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• pp.418-424
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• 2005

We present the design, fabrication and experimental results of 4-bit digital microinjectors, whose ejected droplet volumes are adjusted by the digital operation of a 4-bit microheater array. We design the reference microinjectors as well as its comparative test structures. In the fabrication process, we use a five-mask micromachining process and the total chip size of the fabricated microinjector is $7,640{\mu}m{\times}5,260{\mu}m.$ We measure the ejected droplet volumes and velocities, which are adjusted from $12.1{\pm}1.0~55.6{\pm}14.7pl\;and\;2.3{\pm}0.1~15.7{\pm}0.8m/s.$ respectively, depending on the 15 possible combinations of 4-bit microheater array. We also experimentally characterize the effect of geometric variation including the microheater size, inter-microheater gap, microchannel width and sequential operation of microheater array on the ejected droplet volume and velocity. Among these parameters, we find that the microheater size is the most dominant parameter affected to the ejected droplet volumes and velocities. Thus, the present microinjector has a potential for application to the high-resolution inkjet printers with multiple gray levels or high-precision fluid injectors with variable volume control.