• Journal of computational fluids engineering
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• v.11 no.3 s.34
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• pp.14-21
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• 2006

A numerical simulation of the binary collision dynamics of water drops for size ratios of 1 and 0.75, for the Weber number range of 5 to 100, and for all impact parameter is reported. Two different types of separating collisions, namely reflexive and stretching separations, are identified. A numerical method is based on a fractional-step method with a finite volume formulation and the interface is tracked with Volume of Fluid(VOF) method, including surface tension. Numerical results for size ratios 1 and 0.75 are reasonablely compared with Ashgriz and Poo's experimental results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.1
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• pp.99-112
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• 1997

Mixing process of impinging jets of liquid oxidizer and liquid fuel is simulated by using water and sodium carbonate (Na$_{2}$CO$_{3}$) solution. The shapes of liquid sheets are visualized and flowrate distributions are measured by collecting droplets using measuring cells. Mixing charateristics are studied by using acid-base titration. Stable liquid sheets are formed and two liquid jets are well mixed for symmetric impinging jets. Similarity in flowrate distribution for various measuring heights is observed. For asymmetric impinging jets, liquid sheets become unstable as the difference in the velocities of jets increases. In some extreme cases, liquid sheets are not formed and the jets are separated. Dimensionless variables are adopted demonstrating similarly in flowrate distribution. Mixing characteristics vary significantly with experiment conditions.

• Applied Microscopy
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• v.28 no.3
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• pp.263-271
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• 1998

Oocyte maturation of the swordtail (Kiphophorus hellerii) was investigated by light and electron microscopy. In the ovary of the swordtail, various staged oocytes were observed, Mature oocytes were located in ovarian cortex, meanwhile immature ones were positioned in ovarian medulla. The oocyte was surrounded by several structures or cells such as chorion, follicle cells, follicular theaca and ovarian epithelium, respectively, from the inside toward outside. Growing and maturing oocytes healed numerous microvilli which interconnected the oocyte and the follicle cells to communicate each other. The mature oocyte had the electron dense chorion which appeared to be ultrastructure of two layers and contained pore canals. Oocyte maturation was characterized by not only the enlarged cell size and well differentiated cell organelles, brit also the increases of fat droplets, pinocytotic vesicles and yolk granules.

• Applied Microscopy
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• v.28 no.3
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• pp.273-282
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• 1998

Ultrastructure of fertilized egg envelope in the tomato clown anemonefish (Amphiprion freatus) was examined by mean of light, scanning and transmission electron microscopies. The fertilized egg of tomato clown anemonefish was of non-transparent, ellipsoidal, adhesive and non-floted type, and there were numerous oil droplets in the yolk sac and adhesive filaments in the area of the animal pole. The outer surface of egg envelope was smooth. The fertilized egg envelope consisted of two distinct layers; a non-adhesive outer electron-dense layer and an inner layer, consisting of five horizontal low electron-dense lamellae alternating with the middle electron dense interlamellae.

• Journal of the Korean Society of Combustion
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• v.14 no.3
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• pp.29-36
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• 2009

Simulation is performed to analyze the characteristics of turbulent spray combustion in a diesel engine condition. An extended Conditional Moment Closure (CMC) model is employed to resolve coupling between chemistry and turbulence. Relevant time and length scales and dimensionless numbers are estimated at the tip and the mid spray region during spray development and combustion. The liquid volume fractions are small enough to support validity of droplets assumed as point sources in two-phase flow. The mean scalar dissipation rates (SDR) are lower than the extinction limit to show flame stability throughout the combustion period. The Kolmogorov scales remain relatively constant, while the integral scales increase with decay of turbulence. The chemical time scale decreases abruptly to a small value as ignition occurs with subsequent heat release. The Da and Ka show opposite trends due to variation in the chemical time scale. More work is in progress to identify the spray combustion regimes.

• Journal of Power System Engineering
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• v.16 no.2
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• pp.49-53
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• 2012

Thermal spray coatings developed by deposition of splats, it formed by impacting molten droplets on substrates during thermal spray process. In this study, the Ni-based coatings were fabricated by thermal spray process with two different process parameters, oxygen gas flow and acetylene gas flow, with three different levels of each parameters. The morphology of splats and microstructure were observed by optical microscope. Hardness test were performed on the Ni-based coatings. It was confirmed that process parameters of thermal spray process have effect in morphology of splats. These effects also have important implications on the deposit microstructure and properties of Ni-based coatings.

• Korea-Australia Rheology Journal
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• v.11 no.3
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• pp.241-246
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• 1999

In this study, we consider the effect of nonionic surfactants on the rheological responses of emulsion systems under the action of a uniform do electric field. The model emulsions consist of a less conducting dispersed phase and a more conducting continuous phase. When the shear flow is weak, the positive viscosity effect is produced due to the formation of chain-like morphology. The nonionic surfactants used here generate two distinctively different effects. Specifically, first, the steric hindrance induced by the surfactant molecules renders the structure unstable, and thereby reduces the degree of positive viscosity effect. Secondly, the presence of surfactant molecules also prevents the rotation of the dispersed droplets by anchoring across the interface or by decreasing the size of dispersed phase. The second effect suppresses the negative viscosity effect.

• Journal of computational fluids engineering
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• v.8 no.4
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• pp.6-15
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• 2003

It is an aim of this study to perform extensive numerical study for analyzing the anisotropic turbulence effects on spatial and temporal behaviors of droplet for impinging sprays. The turbulence model of Durbin is used for comparisons with the k-ε model. The turbulence-induced dispersions of droplets are considered to describe the anisotropy of turbulence effectively and spray/wall interactions are simulated using the model of Lee and Ryou. Present study investigates the overall and the internal structures of impinging diesel sprays such as spray shapes, radius and height of wall sprays, Sauter mean diameter (SMD), local droplet velocity, and local gas velocity and compared the results with experimental data by two adopted turbulence models. When the anisotropy effect of turbulence is included, better predictions for both gas and droplet tangential velocities are obtained, compared to the k-ε model. It is concluded that anisotropic effect of turbulence should be considered for simulating impinging diesel sprays.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.4 s.121
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• pp.333-341
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• 2007

Waveform design method for inkjet printing has been proposed tv pressure wave measurement. The pressure wane inside the inkjet dispenser can be effectively measured by current measurement due to self-sensing capability of PZT. The pressure wave measured from current was verified by commercially availablelaser vibrometer. In order to obtain high speed inkjet droplets, two pulse waveform was designed such that the pressure wane after droplet formation can be minimized.

• Journal of the Korean Society of Visualization
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• v.3 no.2
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• pp.3-13
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• 2005

The optical patterantor provides the high resolution and quantitative information of the spray. Fuel distribution and Sauter Mean Diameter (SMD) can be measured from fluorescence and Mie-scat-tering images. To correct the attenuation of the laser beam and signal in dense spray region, the method to find the geometric mean of the signal intensities obtained from two cameras was evaluated and verified in a solid-cone spray. In high pressure environment, the increased number density of the droplets cause multiple scattering. The optical patternation technique using a laser beam instead of a laser sheet was applied to minimize the multiple scattering problem. The pattern of a coaxial spray was changed from hollow-cone to solid-cone shape, and the spray angle was reduced as the ambient pressure increased from 0.1 to 4.0 MPa.