• Nuclear Engineering and Technology
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• v.54 no.6
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• pp.2077-2083
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• 2022

In the unlikely event of core disruptive accident in sodium cooled fast reactors, the reactor containment building would be bottled up with sodium and fission product aerosols. The behavior of these aerosols is crucial to estimate the in-containment source term as a part of nuclear reactor safety analysis. In this work, the evolution of sodium aerosol characteristics (mass concentration and size) is simulated using HAARM-S code. The code is based on the method of moments to solve the integro-differential equation. The code is updated to FORTRAN-77 and run in Microsoft FORTRAN PowerStation 4.0 (on Desktop). The sodium aerosol characteristics simulated by HAARM-S code are compared with the measured values at Aerosol Test Facility. The maximum deviation between measured and simulated mass concentrations is 30% at initial period (up to 60 min) and around 50% in the later period. In addition, the influence of humidity on aerosol size growth for two different aerosol mass concentrations is studied. The measured and simulated growth factors of aerosol size (ratio of saturated size to initial size) are found to be matched at reasonable extent. Since sodium is highly reactive with atmospheric constituents, the aerosol growth factor depends on the hygroscopic growth, chemical transformation and density variations besides coagulation. Further, there is a scope for the improvement of the code to estimate the aerosol dynamics in confined environment.

• Journal of Drive and Control
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• v.21 no.1
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• pp.8-15
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• 2024

This thesis investigates the jetting characteristics of an aerosol jet printing (AJP) process as a function of design and operating conditions. The governing equations of the AJP system are derived for experimentation and analysis. To understand the characteristics of the AJP system, it analyzes the jetting characteristics as a function of the flow rate of the carrier gas and the sheath gas, and the variation of the linewidth with the nozzle exit size based on particle tracking. The thesis focuses on computational fluid dynamics (CFD), which is a computer simulation. The particle tracking results obtained by CFD were analyzed using MATLAB. CFD analytical models can be analyzed in environments with different conditions and consider more specific situations than mathematical computational models. The validity of the CFD analysis is shown by comparing the experimental results with the CFD analysis.

• Journal of Drive and Control
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• v.21 no.2
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• pp.8-14
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• 2024

This paper investigates the jetting characteristics of an aerosol jet printing (AJP) process as a function of design and operating conditions. The governing equations of the AJP system are derived for experimentation and analysis. To understand the characteristics of the AJP system, this thesis analyzes the jetting characteristics as a function of the flow rate of the carrier gas and the sheath gas, and the variation of the linewidth with the nozzle exit size based on particle tracking. This thesis focuses on computational fluid dynamics (CFD), which is a computer simulation. The particle tracking results obtained by CFD were analyzed using MATLAB. CFD analytical models can be analyzed in environments with different conditions and consider more specific situations than mathematical computational models. The validity of the CFD analysis is shown by comparing the experimental results with the CFD analysis.

• Particle and aerosol research
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• v.19 no.3
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• pp.77-87
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• 2023

We present the development of a wetcyclone sampler designed for the sampling of airborne bacteria. The wetcyclone design involves a combination of two traditional cyclone shapes and computational fluid dynamics (CFD) analysis to validate its effectiveness in terms of pressure drop and collection efficiency. The wetcyclone exhibits a collection efficiency of over 90% for bacteria, specifically targeting Staphylococcus aureus. Additionally, the wetcyclone enables continuous bioaerosol sampling using a liquid medium (deionized water), demonstrating a concentration ratio exceeding >105 and a stable microbial recovery rate of 81.9%. The application of real-time quantitative polymerase chain reaction (qPCR) and the colony counting method ensures precise measurement of the concentration ratio and microbial recovery rate.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2005.11a
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• pp.261-262
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• 2005

• Particle and aerosol research
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• v.5 no.2
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• pp.45-52
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• 2009

Black carbon, which is a by-product of combustion of fossil fuel and biomass burning, is the component that imposes the largest uncertainty on quantifying aerosol climate effect. The direct, indirect and semi-direct climate effects of black carbon depend on its state of the mixing with other water-soluble aerosol components. The process that transforms hydrophobic externally mixed black carbon particles into hygroscopic internally mixed ones is called "aging". In most climate models, simple parameterizations for the aging time scale are used instead of solving detailed dynamics equations on the aging process due to the computation cost. In this study, a new parameterization for the black carbon aging time scale due to condensation and coagulation is presented as a function of the concentration of hygroscopic atmospheric components and the black carbon particle size. It is shown that the black carbon aging time scale due to condensation of sulfuric acid vapors varies to a large extent depending on the sulfuric acid concentration and the black carbon particle size. This result indicates that the constant aging time scale values suggested in the literature cannot be directly applied to a global scale modeling. The aging time scale due to coagulation with internally mixed aerosol particles shows an even stronger dependency on particle size, which implies that the use of a particle-size-independent aging time scale may lead to a large error when the aging is dominated by coagulation.

• Journal of the Semiconductor & Display Technology
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• v.21 no.2
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• pp.38-44
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• 2022

Plasma density in semiconductor fabrication equipment becomes higher to achieve the improved the throughput of the process, but the increase of surface corrosion of the ceramic coated chamber wall has been observed by the increased plasma density. Plasma chamber wall coating with aerosol deposition prefer to be firm and uniform to prevent the potential creation of particle inside the chamber from the deformation of the coating materials, and the aerosol discharge nozzle is a good control factor for the deposited coating condition. In this paper, we investigated the design of the nozzle of the aerosol deposition to form a high-quality coating film. Computational fluid dynamics (CFD) study was employed to minimize boundary layer effect and shock wave. The degree of expansion, and design of simulation approach was applied to found out the relationship between the divergence angle and nozzle length as the key parameter for the nozzle design. We found that the trade-off tendency between divergence angle and nozzle length through simulation and quantitative analysis, and present the direction of nozzle design that can improve the uniformity of chamber wall coating.

• Particle and aerosol research
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• v.10 no.2
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• pp.83-91
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• 2014

Since airborne bacteria have been known to aggravate indoor air quality, studies on reducing bacteria particles increase recently. In this study, a chamber(0.8m x 0.8m x 1.56m) system was built in order to simulate real conditions for reducing airborne bacteria, and evaluated by a simple aerosol reduction test. A method utilizing CFD(Computational Fluid Dynamics) simulation was used to detect the horizontal cross-sectional area which represents particle distribution in the chamber. Then an air-cleaner with HEPA filter and Carbon Fiber Ionizer was located on that area for aerosol reduction test. The CFD result found the area was located at 0.2m height from the bottom of the chamber, and the test showed aerosol reduction efficiencies using measurements of number concentration and CFU(colony forming unit) per each case. At the measurement of number concentration, the reduction efficiency of air-cleaner with filter and ionizer(Case 3) was about 90% after 4 minutes from the stop of the bacteria injection, and that with only filter(Case 2) was about 90% after 8 minutes from the beginning. Lastly, that without filter and ionizer(Case 1) was about 30% after 10 minutes. At the measurement of CFU, it shows similar results but it is related to viability of bio-aerosol.

• Asian Journal of Atmospheric Environment
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• v.6 no.4
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• pp.304-313
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• 2012

In this study, the ${\AA}$ngstrom exponent for polydispersed aerosol during dynamic processes was investigated. Log-normal aerosol size distribution was assumed, and a sensitivity analysis of the ${\AA}$ngstrom exponent with regards the coagulation and condensation process was performed. The ${\AA}$ngstrom exponent is expected to decrease because of the particle growth due to coagulation and condensation. However, it is difficult to quantify the degree of change. In order to understand quantitatively the change in the ${\AA}$ngstrom exponent during coagulation and condensation, different real and imaginary parts of the refractive index were considered. The results show that the ${\AA}$ngstrom exponent is sensitive to changes in size distribution and refractive index. The total number concentration decreases and the geometric mean diameter of aerosols increase during coagulation. On the while, the geometric standard deviation approaches monodispersed size distribution during the condensation process, and this change in size distribution affects the ${\AA}$ngstrom exponent. The degree of change in the ${\AA}$ngstrom exponent depends on the refractive index and initial size distribution, and the size parameter changes with the ${\AA}$ngstrom exponent for a given refractive index or chemical composition; this indicates that the size distribution plays an important role in determining the ${\AA}$ngstrom exponent as well as the chemical composition. Subsequently, this study shows how the ${\AA}$ngstrom exponent changes quantitatively during the aerosol dynamics processes for a log-normal aerosol size distribution for different refractive indices; the results showed good agreement with the results for simple analytic size distribution solutions.

• Particle and aerosol research
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• v.5 no.3
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• pp.95-109
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• 2009

A low temperature plasma process has been widely used for semiconductor fabrication and can also be applied for the preparation of solar cell, MEMS or NEMS, but they are notorious in the point of particle contamination. The nano-sized particles can be generated in the low temperature plasma process and they can induce several serious defects on the performance and quality of microelectronic devices and also on the cost of final products. For the preparation of high quality thin films of high efficiency by the low temperature plasma process, it is desirable to increase the deposition rate of thin films with reducing the particle contamination in the plasmas. In this paper, we introduced the studies on the generation and growth of nanoparticles in the low temperature plasmas and tried to introduce the recent interesting studies on nanoparticle generation in the plasma reactors.