• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.12
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• pp.971-978
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• 2007

A spray-wall impingement process of a hollow-cone fuel spray from the high-pressure swirl injector in the Gasoline Direct Injection (GDI) engine were experimented and calculated at various wall geometries. The Linearized Instability Sheet Atomization (LISA) & the Aerodynamically Progressed Taylor Analogy Breakup (APTAB) model and the Gosman model were applied to model the breakup and the wall impingement process of the hollow-cone fuel spray. The numerical modelings were implemented in the modified KIVA code. The calculation results of spray characteristics, such as a spray development process and a radial distance after wall impingement, compared with the experimental results by the Laser Induced Exciplex Fluorescence (LIEF) technique. The droplet size distribution and the ambient gas velocity field, which are generally difficult to obtain by the experimental methods, were also calculated and discussed. It was found that the radial distance after wall impingement and Sauter Mean Diameter (SMD) decreased with increasing a cavity angle.

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.4
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• pp.443-448
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• 2014

This paper describes thermal flow characteristics in various pipelines: straight pipeline and curved pipeline. In the permafrost area, pipelines are exposed to an extremely low temperature ($-40^{\circ}C$). In this situation, three-dimensional flow analysis should be analyzed to investigate thermal effects such as pressure drop, temperature change, velocity deficit and distribution change of liquid droplet of internal fluid. In this paper, multi-phase and multi-species analysis was introduced to analyze the flow characteristics of permafrost pipelines on the vertical support members above ground.

• Journal of Korea Foundry Society
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• v.17 no.5
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• pp.480-487
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• 1997

Particle reinforced metal matrix composites(MMCs) via a centrifugal spray-cast deposition(CSD) process were fabricated by injecting second phase particles($Al_2O_3$<40${\mu}m$, W<17.3${\mu}m$) into copper melt on the atomizing disc. Compositing modes were investigated by combining microstructures and mathematical modeling between Cu droplets and the reinforced particles injected. The $Cu/W_P$ powders were shown that the W particles penetrate and get embedded in the Cu droplets. It is considered that the W particles composite preferentially in Cu melt on the atomizing disc. On the other hand, the $Al_2O_3$, particles did not penetrate into the Cu droplets on the atomizing disc but get attached in surface of Cu droplets during the flight. It is considered that the compositing may be attained in the flight distance which the relative velocity between Cu droplet and $Al_2O_3$, particle is maximum. The microstructure of the $Cu/W_P$ and the $Cu/(Al_2O_3)_p$ composite preform was strongly influenced by compositing modes of droplets, and after subsequent deposition it was comprised as it is called the dispersed type and the cell type of microstructure, respectively.

• Journal of Power System Engineering
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• v.18 no.6
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• pp.21-28
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• 2014

The studies of the spray characteristics for a CRDI engine had been advancing by many researchers, because the performance and exhaust emission were significantly affected with the spray characteristics. But most experiments of the studies would be done at low ambient pressure conditions under 2MPa. In this study, injection rates were measured with Zeuch's method at various ambient pressures to 5MPa and a constant injection pressure of 130MPa. On the same conditions, non-evaporating spray images were taken with a high speed camera and analyzed carefully with Adobe Photoshop CS3. Macroscopic spray characteristics and breakup processes in the spray could be found from the examined and analyzed data. The initial injection rate, penetration, angle, velocity and breakup of the spray were practically affected with a variation of the ambient pressure, but the injection start time and injection period were scarcely affected. As the ambient pressure was higher, the breakup of a high density droplet region in the spray was happened slowly and the main position of breakup was shifted from a front of the spray to a upstream around a nozzle. The results and techniques of spray visualization and injection rate measurement in this study would be practically effective to study a high pressure diesel spray for a CRDI.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.3
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• pp.50-57
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• 2007

Spray characteristics of an injector in a small liquid rocket engine (LRE) is characterized by Particle Image Velocimetry (PIV) and Dual-mode Phase Doppler Anemometry (DPDA). Instantaneous plane images captured by PIV are examined for the qualitative prediction of spray breakup with the setup of evaluation technique for effect of spray angles on injector performance. DPDA is also applied in order to quantify the average velocity, turbulent intensity, SMD, and number density of spray droplets along the spray stream distance leading to precise observation of spray atomization behavior. An objective of the study is the derivation of design parameters of new injectors and the establishment of performance criteria through the clear understanding of spray characteristics.

• Korean Journal of Veterinary Research
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• v.38 no.4
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• pp.898-908
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• 1998

The aim of this experiments were to assess the time-interval change of motional characteristics in frozen-thawed semen of Korean native cattle (KNC) by using computer aided semen analysis (CASA) technology. Twenty-six KNC frozen semen straws were obtained from Korean KNC improvement department, livestock improvement main division, national livestock cooperatives federation in Korea. Specimens were allowed to thaw at $37^{\circ}C$ for 30 sec in water bath. Semen analysis was performed on semen image analysis system (SIAS, Medical supply, Korea) adjusted to the gate settings and used the semen droplet ($5{\mu}l$) placed on Makler counting chamber (Sefi medical instrument, Israel) prewarmed at $37^{\circ}C$. The same person used the same micropipette to fill the Makler counting chamber. A total of 150 or more of sperms were analysed in each specimen by a single trained person by scanning at least 5 to 10 fields. The measurement parameters in SIAS were as follows ; frame rate = 30 frames per sec, image capture = 1 sec, minimum motile speed = $10{\mu}m/s$, maximum countable sperm number = 400. Statistical analysis was done by Student t-test with use of the Sigma plot program on a IBM personal computer. The dancemean(DNM) and hyperactivated sperm(HYP) of frozen-thawed KNC semen kinematics were significantly decreased(p < 0.05) after 10 min of incubation at $37^{\circ}C$ water bath. But, wobble(WOB) of same sample semen was significantly increased(p < 0.05) after 10 min of incubation and significantly decrease(p < 0.05) after 60 min of same incubation. And, after 30 mim of incubation, significantly differences were found most of motion kinematics, motifity(MOT), curvilinear velocity(VCL), straight line velocity(VSL), average path velocity(VAP), amplitude of lateral head displacement(ALH), beat cross frequency(BCF), mean angular displacement(MAD), dance(DNC), on same sample semen. The DNM of KNC semen sample was variable kinematics after 30 min of incubation. Also, the linearity(LIN) and straightness(STR) was significantly decreased(p < 0.05) from 60 min of incubation. In conclusion, the AI within 30 min after thawing of frozen semen can be an effective method for obtaining high fertility rate in KNC reproductive program.

• International Journal of Automotive Technology
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• v.5 no.4
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• pp.221-238
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• 2004

Wall interactions of direct injection spray were investigated using laser-sheet imaging, shadowgraphy, wetted footprint and phase Doppler interferometry techniques. A narrow-cone high-pressure swirl injector is used to inject iso-octane fuel onto a plate, which has three different impact angles inside a pressurized chamber. Heated air and plate conditions were compared with unheated cases. Injection interval was also varied in the heated case to compare dry- and wet- wall impingement behaviors. High-speed macroscopic Mie-scattering images showed that presence of wall and air temperature has only minor effect on the bulk spray structure and penetration speed for the narrow-cone injector tested. The overall bulk motions of the spray plume and its spatial position at a given time are basically unaffected until a few millimeters before impacting the wall. The surface properties of the impact surface, such as the temperature, the presence of a preexisting liquid film also have a small effect on the amount of wetting or the wetted footprint; however, they have strong influence on what occurs just after impact or after a film is formed. The shadowgraph in particular shows that the plate temperature has a significant effect on vapor phase propagation. Generally, 10-20% faster horizontal vapor phase propagation is observed along the wall at elevated temperature condition. For impingement onto a preexisting film, more splash and evaporation were also observed. Contrary to some preconceptions, there is no significant splashing and droplet rebounding from surfaces that are interposed in the path of the DI gasoline spray, especially for the oblique impact angle cases. There also appears to be a dense spray front consists of large sac spray droplets in the oblique impact angle cases. The bulk of the spray is not impacted on the surface, but rather is deflected by it The microscopic details as depicted by phase Doppler measurements show that the outcome of the droplet impaction events can be significantly influenced. Only droplets at the spray front have high enough Weber numbers for wall impact to wet, splash or rebound. Using the sign of vertical velocity, the time-resolved downward droplets and upward droplets are compared. The Weber number of upward moving droplets, which seldom exceeds unity, also decreases as the impact angle decreases, as the droplets tend to impact less and move along the wall in the deflected spray plume.

• Journal of the Korean Society of Food Science and Nutrition
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• v.37 no.10
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• pp.1278-1286
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• 2008

The effect of Tween 20 addition on changes in the stability of methylcellulose (MC) emulsions (1 wt% MC, 10 wt% n-tetradecane, 20 mM bis-tris buffer, pH 7) was investigated by creaming stability and orthokinetic stability measurements. In the case of MC emulsions containing varying amounts of oil (1$\sim$30 wt%) and no Tween 20 added, creaming stability, judged by mean migration velocity of fat globules ($V_m$), was found to depend on droplet size: the larger the droplet size, the worse the stability [$V_m$: 0.326 $\mu$m $min^{-1}$ ($d_{32}$: 0.32 $\mu$m) ${\rightarrow}V_m$: 0.551 $\mu$m $min^{-1}$ ($d_{32}$: 0.53 $\mu$m)]. With Tween 20, creaming stability was found to be worse than the one without Tween 20, except for MC emulsion containing 0.2 wt% Tween 20. In addition, cream stability was the lowest with the lowest concentration of Tween 20 and a tendency to recover with increasing Tween 20 concentration [$V_m$: 0.598 $\mu$m $min^{-1}$ (0.01 wt%)${\rightarrow}V_m$: 0.389 $\mu$m $min^{-1}$ (0.2 wt%)] was found. From viscosity measurement for aqueous bulk phase of MC emulsions, such a change in the creaming stability was found to coincide well with the results of viscosity measurement. Therefore, it was reasonable to say that creaming stability of MC emulsions containing Tween 20 depended on MC concentration in aqueous bulk phase, which was in turn varied by competitive adsorption between MC and Tween 20 at the oil droplet surface. In case of orthokinetic stability, judged by destabilization time ($t_d$), it was found that the addition of Tween 20 resulted in lowered stability with more pronounce tendency at higher concentrations [$t_d$: 160 min (0.03 wt%)${\rightarrow}t_d$: 100 min (0.2 wt%)]. Moreover, combined with previous results, the orthokinetic stability of MC emulsions containing Tween 20 was found to be exponentially proportional to MC load. In conclusion, competitive adsorption between MC and Tween 20 may affect the stability properties of MC emulsion to varying extents, depending on the concentration of Tween 20.

• Journal of computational fluids engineering
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• v.20 no.2
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• pp.23-36
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• 2015

The $2^{nd}$ generation ice accretion analysis program has been developed and validated for various icing conditions. The essential feature of the $2^{nd}$ generation code lies in its capability of handling general 3-D geometry and improved accuracy. The entire velocity fields are obtained based on Navier-Stokes equations in order to take the massively separated flow field into account. Unlike $1^{st}$ generation code, the droplet trajectories are calculated using Eulerian approach, which is adopted to yield appropriate collection efficiency even in the shadow region. For improved thermodynamic analysis on the surfaces, water film model and modified Messinger model are newly included in the present analysis. The ice shape for a given time step is obtained by considering the exact amount of ice accreted on the surface. Each module of the icing analysis code has been seamlessly integrated on the OpenFOAM platform. The developed code was validated against available experimental data for 2D airfoils and 3D DLR-F4. Due to the lack of experimental data, the computed results of DLR-F4 were compared with those obtained from FENSAP-ICE, which is state-of-the-art 3D icing analysis code. It was clearly shown that the present code produces comparable results to those of FENSAP-ICE, in terms of prediction accuracy and the capability of handling general 3-D geometries.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.385-388
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• 2002

The researches of a two-phase atomizers have been carried out in the field of automotive and aerospace industries in order to improve the atomization performance of the liquid droplets ejecting from these nozzles. The smaller droplets have the advantages of the reduction of environmental pollution matter and effective use of energy through the improvement of heat and mass transfer efficiency. Thus, to propose the basic information of two-phase flow, an internal mixing atomizer was designed, its shape factor was 0.6 and the liquid feeding hole was positioned at the center of the mixing tube which was used to mix the air and liquid. The experimental work was performed in the field after the nozzle exit orifice. The measurement of the liquid droplets was made by PDPA system. This system can measure the velocity and size of the droplets simultaneously. The number of the droplets used in this calculation was set to 10,000. The flow patterns were regulated by ALR (Air to Liquid mass Ratio). ALR was varied from 0.1024 to 0.3238 depending on the mass flow rate of the air. The analysis of sampling data was mainly focused on the spray characteristics such as flow characteristics distributions, half-width of spray, RMS, and turbulent kinetic energy with ALR.