• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.3
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• pp.219-224
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• 2020

Al₂O₃ powders with particle sizes of 0.35 ㎛, 0.5 ㎛, 1.5 ㎛, and 2.5 ㎛ are deposited onto glass and Cu substrates using the aerosol deposition (AD) process. The deposition characteristics of Al₂O₃ films using those four types of Al₂O₃ powders are investigated to determine the influence of the particle size on the films. To observe detailed micro-structures of the films, the cross-section and surface morphology are observed. Then, the crystalline size and internal strain are calculated from X-ray diffraction peaks in order to confirm the hammering effect as well as the micro-strain during the AD deposition. From the above results, deposition mechanisms related to the particle size are studied. The results of this study indicate the optimal particle size and formation mechanisms for dense Al₂O₃ film with a smooth surface roughness as well as for a porous Al₂O₃ film with a rough surface roughness.

• Particle and aerosol research
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• v.11 no.4
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• pp.99-105
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• 2015

The possible existence forms of particle aggregates in liquid medium are classified into four different types according to their morphological characteristics, including the single particles that are separated from each other, the linear aggregates in which all component particles are located in a line, the planar aggregates where all particles are arranged on a plane, and the volumetric aggregates where all particles forms a three-dimensional space. These particle aggregates with different space morphologies have different fractal dimensions and different influence on the rheological phenomena of the solid-liquid system. The effects of various aggregates on the suspension viscosity are analyzed and related with the particle concentration, and then a mathematical model is presented to determine the fractal dimensions of various aggregates by measuring the apparent viscosity of the solid-liquid system. In the model, the viscous fractal dimension is developed as a new concept, the fractal dimensions of different aggregates can be obtained separately and then the relative components of various aggregates experimentally analyzed.

• Particle and aerosol research
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• v.8 no.2
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• pp.55-68
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• 2012

Particulate matters (PM) which are collected into a diesel particulate filter (DPF) system have to be periodically removed by thermal oxidation. In this report, we fabricated an electrohydrodynamic-assisted pressure-swirl nozzle to spray diesel droplets finer. Atomization performance of the nozzle was evaluated using both experimental and numerical methods. Two types of nozzle designs, the charge induction type and the charge injection type, were tested. While the former generated diesel droplets of $400\;{\mu}m$ at an applied electric potential over 10 kV, the latter presented the droplets smaller than $23\;{\mu}m$ at an applied electric potential of 8 kV. The numerical simulation results showed that the reduced size of droplets caused higher evaporation of droplets and therefore the increased temperature, which would eventually increase the regeneration performance of the DPF system.

• Particle and aerosol research
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• v.9 no.2
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• pp.59-67
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• 2013

One of purposes in this study was to confirm the behavior of coughed particles under different ventilation conditions. Three types of ventilation systems were applied for this experiment and the properties of coughed particles were measured using computational fluid dynamics (CFD) in an intensive care unit. The changes of total airborne particles for each case showed different trends according to the ventilation type and time, but the deposited particles were similar in all conditions. Although the time taken for 50% of the particles to be deposited was the fastest in case 2, the portion of deposited particles after 300 seconds was only 5% in all conditions. In case 1, a relatively small number of particles were deposited on the wall, but the particle exhaust and deposition on the occupants were the highest. In case 3, the downward ventilation was applied as that recommended by the US Center for Disease Control and Prevention (CDC) and showed different exhaust efficiencies according to the particle size.

• Particle and aerosol research
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• v.15 no.1
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• pp.27-36
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• 2019

Numerical analysis has been conducted on three-dimensional airflow distribution in the passenger cabin of a high-speed electric train. The types of air distribution systems investigated in the present study were those of TGV and Shinkansen. The Reynolds-averaged Navier-Stokes equations governing the mass and momentum conservations of the airflow in the cabin were solved by using a finite volume method, which are coupled with the standard $k-{\varepsilon}$ turbulence model equations. Predicted velocity distributions were presented on several selected planes in the passenger cabin. The present three-dimensional simulations were found to show the overall features of the airflow in the passenger cabin fairly well. In particular, it was shown that the type of air distribution for Shinkansen was more suitable for a non-smoking cabin than that for TGV.

• Nuclear Engineering and Technology
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• v.55 no.1
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• pp.12-24
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• 2023

With the improvement of laser technology, the strategic needs of efficient and precise decontamination of various components in nuclear application units can be fulfilled by laser decontamination. The surface contaminants of nuclear facilities mainly exist both as loose contaminated layer and fixed oxide layer. The types of radionuclides and contamination layer thickness are closely related to the operation status of nuclear facilities, which have an important influence on the laser decontamination process. This study reviewed the mechanism of laser surface treatment and the influence of laser process parameters on the decontamination thickness, decontamination factor, decontamination efficiency and the distribution of aerosol particle. Although multiple studies have been performed on the mechanism of laser processing and laser decontamination process, there are few studies on the microscopic process mechanism of laser decontamination and the influence of laser decontamination on surface properties. In particular, the interaction between laser and radioactive contaminants needs more research in the future.

• Journal of Environmental Science International
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• v.29 no.1
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• pp.79-93
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• 2020

To determine the size distributions of water-soluble inorganic ionic species (WSIS) in roadside aerosols, sampling experiments were carried out in the urban roadside area of Jeju City on August 2018 and January 2019 by using the eight-stage cascade impactor sampler. The mass of roadside aerosols were partitioned at 57% in fine fraction, 36-37% in coarse fraction, and 6-7% in giant fraction, regardless of summer and winter. The mass concentrations of WSIS except for Na+ and SO42- in roadside aerosols were higher in winter than in summer. The size distributions of Na⁺, Mg²⁺, Ca²⁺ and Cl^- were characterized by bimodal types with coarse particle mode peaking around 3.3-4.7 ㎛ and 5.8-9.0 ㎛. The size distributions of NO₃^- and K⁺ shifted from a single fine mode peaking around 0.7-1.1 ㎛ in winter to bimodal and/or trimodal types with peaks around coarse mode in summer. SO₄^2- and NH₄⁺ showed a single fine mode peaking around 0.7-1.1 ㎛. The MMAD of roadside aerosols was lower than that of Na⁺, Mg²⁺, Ca²⁺ and Cl-. Based on the marine enrichment factors and the ratio values of WSIS and the corresponding value for sea water, the composition of roadside aerosols in Jeju City may be practically affected by terrestrial sources rather than marine source.

• Particle and aerosol research
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• v.12 no.2
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• pp.43-50
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• 2016

The influence of basalt fibres on the compressive strength of the geopolymer type binders has been studied. For the experiments 2 types of the basalt fibres were used, namely chopped and spooled fibres. Both types of basalt fibres were 7-10 micron thick in diameter and cut into pieces of 6 mm length. The fibres were mixed with 1% weight to the fly ash powder, followed by the addition of the activator solution (8M NaOH). The pastes obtained were cured at $70^{\circ}C$ for 20 h revealing compact bodies. Compressive strength was measured after 7 days and microstructure observation performed with SEM. The cube bodies ($2{\times}2{\times}2cm$) reveal compressive strength of 47.25(4.03) MPa, while it decreased to 34.0(9.05) MPa in spooled basalt fibres and to 17.33(5.86) MPa in the chopped basalt fibres containing binder, i.e 76% and 36% of the strength without fibres, respectively. The much weaker compressive strength of the chopped fibres containing binder is related to the absence of significant adhesion between the geopolymer binder and the basalt fibres, forming voids instead. Alkali leaching effect of basalt fibres could probably explain the drop in the compressive strength with spooled and chopped fibres, respectively.

• Korean Journal of Remote Sensing
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• v.37 no.6_2
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• pp.1891-1900
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• 2021

Fine particulate matter (FPM; diameter ≤ 2.5 ㎛) is frequently found in metropolitan areas due to activities associated with rapid urbanization and population growth. Many adolescents spend a substantial amount of time at school where, for various reasons, FPM generated outdoors may flow into indoor areas. The aims of this study were to estimate FPM concentrations and categorize types of FPM in schools. Meteorological and chemical variables as well as satellite-based aerosol optical depth were analyzed as input data in a random forest model, which applied 10-fold cross validation and a grid-search method, to estimate school FPM concentrations, with four statistical indicators used to evaluate accuracy. Loose and strict standards were established to categorize types of FPM in schools. Under the former classification scheme, FPM in most schools was classified as type 2 or 3, whereas under strict standards, school FPM was mostly classified as type 3 or 4.

• Journal of Korean Society for Atmospheric Environment
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• v.32 no.6
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• pp.593-602
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• 2016

The physicochemical characteristics of particulate matter emissions from various vehicle's fuel types were studied at the facility of Transport Pollution Research Center(TPRC), National Institute of Environmental Research (NIER), Korea. Three different types of fuels such as gasoline, liquefied petroleum gas (LPG) and diesel were tested on the NIER driving mode and the constant speed modes(30, 70, and 110 km/h). Chemical composition of submicron particles from vehicle emissions was measured by the High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS) during running cycles. Organics were dominant chemical species of particulate matter emissions for all three different vehicles' fuel types. Moreover, regardless of fuel types, emission rate of organics and inorganics decreased as the average speed of vehicle increased. The portion of fully oxidized fragment families of $C_xH_yO_z$ accounted for over 98% of organic aerosol(OA) in LPG and diesel vehicles, while the relatively high fraction of $C_xH_y$ in OA was observed in gasoline vehicle.