• Journal of Advanced Marine Engineering and Technology
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• v.24 no.5
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• pp.103-110
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• 2000

A two phase compound jet, which mixes pulverized solid particles with the air in the test section, is experimentally analyzed in this study. Two phase flow is jetted 10 degree upward in the primary jet, while the secondary jet utilizes the air only. The height difference between the primary and secondary central axises is 32.5mm. The velocity vector field, concentration field, and turbulent properties of solid particles are measured by using 3-Dimensional Particles Dynamics Analyzer. When the jet angle of the secondary jet goes into effect, the solid particle recirculation zone becomes larger. Also, solid particle concentration becomes more dense due to a velocity decrement of particles.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.06a
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• pp.160-173
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• 1997

Microstructure of hypereutectic Al-17wt.% Si alloy, fabricated by mechanical stirring and by reheating at semi-solid state, was investigated by optical microscope. Flow behavior semi-solid metal also was investigated at diffentent mould temperatures 280$^{\circ}C$, 290$^{\circ}C$ and 300$^{\circ}C$. Size of silicon particles were increased over 100$\mu\textrm{m}$ during solidification as a result of stirring. It is considered as microstructural coarsening by bonding between neighbouring primary silion particles during stirring of slurry. In case of reheating at semi-solid state, however, primary silicon particle was not increased at size of 40$\mu\textrm{m}$ and nearly spherical aluminum solde particle also could be obtained uniformly in distribution. The fludity of Al-17wt.% Si alloys at semi-solid state was improved when solid fraction was 0.7 at mould temperature of 300$^{\circ}C$ than other conditions.

• Journal of Energy Engineering
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• v.1 no.1
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• pp.76-86
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• 1992

A three-dimensional model has been developed for pulverized coal combusters and gasifiers. Coal devolatilization, heterogeneous char oxidation, gas particle interchange, radiation, gas phase oxidation, primary and secondary stream mixing, and heat losses are considered. A finite difference method was used to solve the ordinary non-linear differential equations. The effects of primary and secondary stream flow ratio and coal particle size are investigated.

• Korean Chemical Engineering Research
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• v.53 no.4
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• pp.440-444
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• 2015

Effects of operating variables on the solid circulation rate were investigated in a three-phase circulating fluidized bed, of which inside diameter was 0.102m and height was 3.5m, respectively. Gas velocity, primary and secondary liquid velocities, particle size and height of solid particles piled up in the solid recycle device were chosen as operating variables. The solid circulation rate increased with increasing primary and secondary liquid velocities and height of solid particles piled up in the solid recycle device, but decreased with increasing particle size. The value of solid circulation rate decreased only slightly with increasing gas velocity in the riser. The values of solid circulation rate were well correlated in terms of dimensionless groups within the experimental conditions.

• Journal of the Korean Ceramic Society
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• v.35 no.10
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• pp.1049-1054
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• 1998

In order to fabricate ideal powders new processing is necessary in which the solute atoms in solution ra-pidly move to mix each other to the degree of molecular level the viscosity of solution should be low not to effect the moving of solute atoms and the powders could be directly obtained as crystalline. Supercritical fluid is defined as condensed gas sated up to its critical pressure and temperature. In this paper su-percritical fluid methods were studied as a new ceramic processing of powder preparation. The crystalline powders of TiO2 which are useful for electronic ceramic materials were fabricated by hydrolysis of titanium (IV) ethoxide using ethanol as a supercritical fluid at the condition of 270$\pm$3$^{\circ}C$, 7.3 MPa for 2hr. The cry stalline anatase powders could be directly obtained and its primary particle size was 20 min.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.6
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• pp.714-724
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• 1985

Two-phase(air-solid, air-liquid droplet) turbulent round jet has been analyzed numerically using two equation turbulence model. The mean motion of suspending particles in air has been treated as the secondary fluid with virtual density and eddy viscosity. In this paper, the local mean velocity of secondary fluid is not assumed to be the same as that of the primary one. Dissipation rate of turbulent kinetic energy which arises because the particles can not catch up with the turbulent fluctuations of the primary fluid has been modelled by using the concept of Kolmogorov's spectral energy transfer. Numerical computations were performed for flows with different volume fraction of the dispersed phase and the diameter of particle. Results show that the total rate of turbulent energy dissipation, turbulent intensities and spreading rate of jets are reduced by the increase of volume fraction of dispersed phase. However it does not show consistent tendency with increasing the particle diameter. This investigation also shows that presence of particles in the fluid modifies the structure of the primary fluid flow significantly. Predicted velocity profiles and turbulence properties qualitatively agree with available data.

• Particle and aerosol research
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• v.20 no.1
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• pp.13-24
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• 2024

The concentrations of polycyclic aromatic hydrocarbons (PAHs) and elemental carbon (EC) in particulate matter, typical primary aerosols have decreased in Seoul between 2003 and 2018 (80% for PAHs and 85% for EC). The yearly mean benzo[a]pyrene (BaP) concentration has been lower than 1 ng/m3 since 2010-2011, the target value set by the European Union (EU) and China. A series of policies related to solid fuel and vehicle in South Korea and China should be effective in the reduction of the ambient PAHs and EC concentrations. But the emission data of PAHs and EC at both countries did not support that hypothesis. Possible causes are uncertainties in the emission inventories of primary carbonaceous aerosols in South Korea and China, although there may be a minor effect of the emissions from North Korea on the concentrations in Seoul. Thus the further policy directions against PAHs and EC such as improvements of emissions inventories and measurements, intensive regulation of non-road mobile sources and control of PAHs derivatives are discussed.

• Particle and aerosol research
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• v.9 no.3
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• pp.133-137
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• 2013

Measuring particle size distribution is one of the primary concerns in aerosol studies. For a nano-particle size distribution measurement, many scientists use a combination of a differential mobility analyzer (DMA) and a condensation particle counter (CPC) system, which is a called scanning mobility particle sizer (SMPS). Although it has a very high particle size resolution, some issues still remain. These problems include residence time between a DMA and a CPC, discontinuity of a CPC, and disturbance due to long scanning time during the precise measurement of particles. In particular, long scanning time is not adequate for measuring particle size distribution since the particle concentration is changing during the measurement. In this study, we developed radial exhaust multi-port system (REM-system) with no scanning time and high resolution to measure real-time particle size distribution. As a result of the REM-system performed using mono-disperse particle, it is expected that this system will be suitable for measuring continuously changing aerosol. If the counting efficiency of multi-condensation particle counter (M-CPC) and data inversion matrix are completed, REM-system will be a very adequate system for unsteady aerosol, which changes for SMPS scanning time.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.381-384
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• 2001

The combined stirring method to uniform distribution of particle is consisted of two strring force both electro-magnetic stirring generated from induction heating and mechanical stirring with graphite stirrer. PMMC billets were fabricated with the volume fractions ranged from 0% to 20% and particle sizes ranged from 14$\mu\textrm{m}$ to 25$\mu\textrm{m}$. It is important to control the size of primary ${\alpha}$-AI solid particles because it could become the cause of the particle pushing or capture phenomena from the fact that secondary dendrite arm spacing size depends on the cooling rate during the solidification in hypoeutectic AI-Si alloy.

• Journal of Korean Society of Water and Wastewater
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• v.19 no.6
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• pp.775-780
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• 2005

This study was performed to investigate the effect of foulant characteristics on Membrane fouling index such as Silt Density Index (SDI) and Modified Fouling Index (MFI). A linear relationship was found relating the fouling index (both SDI and MFI) on particle concentration, but fouling index values were nonlinearly (exponentially) with increasing organic concentration. When organic matter was the primary cause of fouling, the MFI was not accurately predicted due to internal fouling such as pore adsorption. The fouling index was determined mainly by particle characteristics when both particle and organic coexisted in the feed water. This observation was attributed to lessening of organic pore adsorption by particle cake layer formed on the membrane surface. Bench-scale actual fouling experiments demonstrated that permeate flux declines much faster with feed water containing particles than organic matters although fouling potential predicted by SDI values were identical, indicating that the accurate prediction of fouling potential requires the development of fouling index reflecting different foulant characteristics.