• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.8
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• pp.1056-1067
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• 1997

Present study visualized flow pattern and investigated spray characteristics of twin-fluid atomization with converging-diverging nozzles. Particle sizes were measured by using the Malvern particle analyzer, and the radial size distributions were evaluated by using the tomographic transform technique. The results show that the SMD generally increases in the radial direction at a prescribed liquid flow rate and the increasing rate in the SMD becomes gradual as atomizing gas pressure increases. The SMD decreases as the liquid flow rate increases at a fixed GLR (gas/liquid mass ratio). The atomization performance of the protrusion-type nozzle turned out to be superior to that of the flush-type. However, in the case of the protrusion-type, flow separation occurs outside the liquid delivery tube when the pressure at the gas nozzle chamber is high enough, which may deteriorate the atomization performance.

• Particle and aerosol research
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• v.4 no.2
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• pp.69-75
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• 2008

Nanosize ZnO particles were prepared by oxidation of zinc vapor and the particle growth was modeled by a coagulation model by assuming that the characteristic time for reaction was much shorter than coagulation time and residence time (${\tau}_{reaction}{\ll}{\tau}_{coagulation}{\ll}{\tau}_{residence}$). Experimental measurement of zinc oxide particles diameter was consistent with the predicted result from the coagulation model. For practical purpose of predicting zinc oxide size in areosol reactor, the constant kernel solution is concluded to be sufficient, Uniqueness of nano-scale property of zinc oxide was confirmed by the higher photocatalytic activity of zinc oxide than nanosize titania particles.

• Wind and Structures
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• v.4 no.5
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• pp.441-454
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• 2001

Conical vortices on roof corners of a prismatic low-rise building have been investigated by using the PIV(Particle Image Velocimetry) technique. The Reynolds number based on the free stream velocity and model height was $5.3{\times}10^3$. Mean and instantaneous vector fields for velocity, vorticity, and turbulent kinetic energy were measured at two vertical planes and for two different flow angles of $30^{\circ}$ and $45^{\circ}$. The measurements provided a clear view of the complex flow structures on roof corners such as a pair of counter rotating conical vortices, secondary vortices, and tertiary vortices. They also enabled accurate and easy measurement of the size of vortices. Additionally, we could easily locate the centers of the vortices from the ensemble averaged velocity fields. It was observed that the flow angle of a $30^{\circ}$ produces a higher level of vorticity and turbulent kinetic energy in one of the pair of vortices than does the $45^{\circ}$ flow angle.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.5
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• pp.196-203
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• 2005

A semi-empirical method to determine the electrostatic characteristics of a diode type corona aerosol charger based on ion current measurement and electrostatic charging theory was presented. Results from mathematical model were in agreement with those from experimental investigation of the charger. Current-voltage characteristics, $N_{i}t$ product and charge distribution against aerosol size were obtained. It was shown that the space charge was significant and must be taken into account at high ion number concentration and low flow rate. Additionally, significant particle loss was evident for particles smaller than 20 nm in diameter where their electrical mobility was high. Increase in charging efficiency may be achieved by introducing surrounding sheath flow and applying AC high voltage. Overall, the approach was found to be useful in characterizing the aerosol charger.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.10
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• pp.78-85
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• 2004

The particle amount monitoring technique using ultrasound is proposed to determine the proper maintenance time of the filter in the supply process of pure gas in the unit of oxygen plant. There are advantages that it is adaptable in high temperature and high pressure, and it is not disturbed by being exposed in the gas flow, and it can be implemented very economically. The applicability of the ultrasonic technique is pre-studied through the theoretical analysis for the dependency of attenuation of ultrasonic wave on the particles in the gas flow. For the purpose, absorption, scattering and dispersion models are considered, and the attenuation by absorption and the change rate of the propagation speed are calculated fur the specific range of particle size and the ultrasonic wave frequency. It was expected by simulation that the absorptive attenuation by particles was the most sensitive to the change of particle amount. The experimental result showed high correspondence with the theoretical expectation so that this ultrasound attenuation measurement was proved to be highly effective for monitoring the amount of floating particles in the gas flow.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.157-163
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• 2011

Combustion of magnesium dust particle were fabricated test devices and combustion experiments were carried out. The ignition delay time were measured in change of magnesium particle mass flow rate in premixed flame. According to increasing magnesium particle mass flow rate, ignition delay time were more shorter. In addition, magnesium dust combustion temperature were measured different particle sizes and o/f ratio by two wavelength pyrometry. Dust combustion flame temperature is almost similarly, through to equivalence ratio, confirm the combustion flame temperature range characteristics.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.6
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• pp.847-853
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• 2008

Although combustion is essential in most energy generation processes, it is one of the major causes of air pollution. Circle fin exhaust pipes were designed to study the effect of cooling the recirculated exhaust gases (EGR) of Diesel engines on the chemical composition of the exhaust gases and the reduction in the percentages of pollutant emissions. The designs adopted in this study were exhaust pipes with solid and hollow fins around them direct surface force measurement in water using a nano size colloidal probe Technique The direct force measurement between colloidal surfaces has been an essential topic in both theories and applications of surface chemistry. As particle size is decreased from micron size down to true Carbon nano Colloid size (<10nm), surface forces are increasingly important. Nanoparticles at close proximity or high solids loading are expected to show a different behavior than what can be estimated from continuum and mean field theories. This paper use Water and CNC fluid at normal cooling system of EGR. Experimental result showed all good agreement at Re=$2.54{\times}10^{4}$.

• Fashion & Textile Research Journal
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• v.10 no.3
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• pp.371-376
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• 2008

Poly(ethylene-co-vinylacetate) (EVA) microspheres were prepared by thermally induced phase separation (TIPS) in toluene. The microsphere formation occurred by the nucleation and growth mechanism in metastable region. The effects of the concentration and component of the polymer and cooling rate on microsphere formation were investigated. The microsphere formation and growth were followed by the cloud point of the optical microscope measurement. The microsphere size distribution, which was obtained by particle size analyzer, became broader when the polymer concentration was higher, the content of vinyl acetate in EVA copolymer was higher, the cooling rate of EVA copolymer solution were lower. The content of disperse dye in EVA microsphere was obtained by TGA thermal analysis, the dye content of EVA15 and EVA18 were 3.5 and 2.0 wt% respectively.

• Particle and aerosol research
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• v.8 no.4
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• pp.151-160
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• 2012

Health effects caused by the ultrafine particles in ambient air are great concern to the public health, and the strict measuring and monitoring of the ambient aerosol are required. In this work, the characteristics of the aerosol size distribution in Pohang province are studied. Optical particle counters (Grimm APS 1108 and 1109) were used to measure the aerosol size distribution in the area. Locations near the national monitoring site located in the industrial and the residence area were selected for the measuring sites of this study, and the locations in border area between the industry and the residence were selected for the reference of the comparison. In the industry site, it is found that the concentration of aerosol particles near the size of 5 ${\mu}m$ appear characteristically and the fluctuations in concentration with respect to time are minimal. The mass concentration of the aerosol above 10 ${\mu}m$ in diameter in the industry area was found to fluctuate significantly. The mass portion of $PM_{10}$ and PM2.5 to TSP in the residence area were 83% and 51% respectively. In the industrial regional, it was found that the mass portion of PM10 and $PM_{2.5}$ to TSP were 76% and 35% respectively. In the boundary area the mass portion of $PM_{10}$ and $PM_{2.5}$ to TSP were 78% and 54% respectively.

• Journal of Environmental Science International
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• v.22 no.3
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• pp.347-358
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• 2013

The aerosol number concentration have measured with an aerodynamic particle sizer spectrometer(APS) at Gosan in Jeju Island, which is known as background area in Korea, from March 2010 to February 2011. The obtained results of asian dust events and non-asian dust period have been compared. The results show that the entire averaged aerosol number concentration from APS measurement during asian dust events and non-asian dust period are about 341 particles/$cm^3$ and 240 particles/$cm^3$, respectively. During asian dust events, the number concentration in small size ranges(${\leq}0.4{\mu}m$) are similar to non-asian dust period, however, those in large size ranges(${\geq}0.7{\mu}m$) are very higher than non-asian dust period. The contributions of the size resolved number concentration(23 channel in $0.25{\sim}10.0{\mu}m$) to total number concentration in that range are dramatically decreased with increased particle size. The contributions of smaller size ranges(${\leq}0.4{\mu}m$) during asian dust events are very low compared with non-asian dust period, on the other hand, those of larger size ranges(${\geq}0.4{\mu}m$) are higher than non-asian dust period. The number concentration in each size range are strongly correlated with the concentration in adjacent size range. And the total aerosol number concentration are depended on the number concentration in range of smaller than $0.58{\mu}m$ during non-asian dust period and asian dust events. On the other hand, $PM_{10}$ mass concentration has mainly affected with the number concentration in range of smaller than $1.0{\mu}m$ during non-asian dust period, however, during asian dust events, the mass concentration has mainly affected with the number concentration in range of $0.65{\sim}3.0{\mu}m$.