• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.546-550
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• 2008

In this study, 3-dimensional Computational Fluid Dynamics (CFD) analysis was induced to simulate air flow and particle motion in the axial flow cyclone separator. The commercialized CFD code FLUENT was used to visualize pressure drop and particle collection efficiency inside the cyclone. We simulated 4 cyclone models with different shape of vane, such as turning angle or shape of cross section. For the air flow simulation, we calculated the flow field using standard ${\kappa}-{\varepsilon}$ turbulence viscous model. Each model was simulated with different inlet or outlet boundary conditions. Our major concern for the flow filed simulation was pressure drop across the cyclone. For the particle trajectory simulation, we adopted Euler-Lagrangian approach to track particle motion from inlet to outlet of the cyclone. Particle collection efficiencies of various conditions are calculated by number based collection efficiency. The result showed that the rotation angle of the vane plays major roll to the pressure drop. But the smaller rotation angle of vane causes particle collection efficiency difference with different inlet position.

• Korean Journal of Pharmacognosy
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• v.44 no.2
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• pp.118-124
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• 2013

Mast cells is the key effector cells for IgE-mediated allergic responses. In this study, we investigated whether Rhus trichocarpa extract (RT) inhibited IgE-mediated allergic responses in mast cells and an allergic animal model. We further tried to find its mechanism of action in mast cells. We found that RT suppressed antigen-stimulated degranulation and production of TNF-${\alpha}$ and IL-4 in rat basophilic leukemia (RBL)-2H3 mast cells and bone marrow-derived mast cells (BMMC), as well as IgE-mediated passive cutaneous anaphylaxis (PCA) in mice. As the mechanism of action of RT, it inhibited the activation of spleen tyrosine kinase (Syk), a pivotal signaling molecule for activation of mast cells and that of LAT, a downstream adaptor molecule of Syk in $Fc{\varepsilon}RI$-mediated signal pathways. RT also suppressed the activation of mitogen-activated protein (MAP) kinases and Akt. The current results demonstrated for the first time that RT has the anti-allergic effect through inhibiting degranulation and secretion of cytokines by suppression of Syk in antigen-stimulated mast cells. Therefore, RT might be useful for allergic diseases.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.4
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• pp.561-575
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• 1996

The interaction of turbulent mixed convection and surface radiation in a three-dimensional channel with the heated blocks is analyzed numerically. Two blocks are maintained at high temperature and the other bottom and horizontal walls are insulated. S-4 method is employed to calculate the effect of the radiative heat transfer. The low Reynolds number k-$\varepsilon$ model proposed by Launder and Sharma is used to estimate the turbulent influence on the heat transfer enhancement. From above modeling, the effects of various channel specifications on the flow and heat transfer characteristics are investigated. The variables used for the present study are Reynolds number, block spacing, the channel height spacing for block and the emissivity. Average Nusselt numbers along the block surfaces are correlated and presented in terms of Reynolds number, emissivity and dimensionless geometric parameters. For the range of conditions in this study, average Nusselt numbers along the block surfaces are strongly influenced by the Reynolds numbers and channel height spacing for block but weakly influenced by the block spacing and the emissivity of the adiabatic walls.

• The Korean Journal of Ceramics
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• v.1 no.1
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• pp.13-20
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• 1995

Effects of thermal annealing on the dielectric/piezoelectric properties of $Pb(Zn, Mg)_{1/3}Nb_{2/3}O_3-PbTiO_3$ ceramics (PZMNPT) with Zn/Mg=6/4) were examined across the rhombohedral/tetragonal morphotropic phase boundary (MPB). Both the relative dielectric permittivity ($\varepsilon$r)and the piezoelectric constant($d_33$)/electromechanical coupling constant ($k_p$)were increased by thermal annealing ($800^{\circ}$~$900^{\circ}C$) after sintering at $1150^{\circ}C$ for 1 hr. Based on the dielectric analysis using the series mixing model and the concept of a random distribution of the local Curie points, the observed improvements in the dielectric and piezoelectric properties of PZMN-PT were interpreted in terms of the elimination of PbO-rich amorphous intergranular layers(~1nm) induced by thermal annealing. A concrete evidence of the presence of amorphous grain-boundary layers in the unannealed (as-sintered) specimen was obtained by examining the structure of intergranular region using a TEM.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.556-560
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• 2011

The seawater lift pump system is responsible for maintaining the open canal level to provide the suction flow of circulating water pump at the set point. The objective of this paper is to design a 2-stage mixed flow pump(for seawater lifting) by inverse design and to evaluate the overall performance and the local flow fields of the pump by using a commercial CFD code. Rotating speed of the impeller is 1,750 rpm with the flow rate of 2,700 $m^3/h$. Finite volume method with structured mesh and Realizable ${\kappa}-{\varepsilon}$ turbulent model is used to guaranty more accurate prediction of turbulent flow in the pump impeller. The numerical results such as static head brake horse power and efficiency of the mixed flow pump are compared with the reference data. Also, the periodic condition calculation method for the mixed flow pump was carried out in order to investigate the pump performance characteristics with the modification of impeller geometry.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.28 no.2
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• pp.190-199
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• 2018

Objectives: The purpose of this case study is to assess the current airflow and find the ideal ventilation conditions in tank reactors for minimizing the possibility of exposure respiratory dusts(size of $2.5{\mu}m$, $10{\mu}m$) when workers exchange catalysts in the tank reactors. Methods: A Numerical study was performed to determine ideal ventilation conditions, We considered two sizes of airborne respiratory particles($2.5{\mu}m$, $10{\mu}m$) at 12points from the bottom of tank reactor. We changed input & output ventilation conditions and analyzed the particle motion in the tank reactor. The star-ccm+, computational fluid dynamics tool was used to predict air & particle flow patterns in the tank reactor and a numerical simulation was achieved by applying the realized ${\kappa}-{\varepsilon}$ turbulence model and the Lagrangian particle tracking method. Results: From the results, the increase of recirculation air had a significant impact on removing dusts because they are removed by HEPA filter. To the contrary, Increasing the clean air quantity or changing the input position of clean air is not good for workers because it causes the exit of respiratory dusts through workers' entrance or cause it to remail suspended in the air in the workplace tank.

• Journal of Power System Engineering
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• v.22 no.1
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• pp.11-17
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• 2018

The steady-state, incompressible and three-dimensional numerical analysis was carried out to evaluate the internal flow fields characteristics of wind tunnel contractions made by Morel's curve equations. The turbulence model used in this study is a realizable ${\kappa}-{\varepsilon}$ well known to be excellent for predicting the performance of the flow separation and recirculation flow as well as the boundary layer with rotation and strong back pressure gradient. As a results, when the flow passes through the interior space of the analytical models, the flow resistance at the inlet of the plenum chamber is the largest at $Z_m=300$, 400 mm, but the smallest at $Z_m=700mm$. The maximum turbulence intensity in the test section is about 2.5% when calculated by the homogeneous flow, so it is improved by about 75% compared to the 10% turbulence intensity at the inlet of the plenum chamber due to the contraction.

• Wind and Structures
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• v.15 no.4
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• pp.313-329
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• 2012

There have existed for a number of years good practice guidelines for the use of Computational Fluid Dynamics (CFD) in the field of wind engineering. As part of those guidelines, details are given for the size of flow domain that should be used around a building of height, H. For low-rise buildings, the domain sizes produced by following the guidelines are reasonable and produce results that are largely free from blockage effects. However, when high-rise or tall buildings are considered, the domain size based solely on the building height produces very large domains. A large domain, in most cases, leads to a large cell count, with many of the cells in the grid being used up in regions far from the building/wake region. This paper challenges this domain size guidance by looking at the effects of changing the domain size around a tall building. The RNG ${\kappa}-{\varepsilon}$ turbulence model is used in a series of steady-state solutions where the only parameter varied is the domain size, with the mesh resolution in the building/wake region left unchanged. Comparisons between the velocity fields in the near-field of the building and pressure coefficients on the building are used to inform the assessment. The findings of the work for this case suggest that a domain of approximately 10% the volume of that suggested by the existing guidelines could be used with a loss in accuracy of less than 10%.

• Structural Engineering and Mechanics
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• v.27 no.2
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• pp.135-148
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• 2007

A new finite shear wall element model and a method for calculation of 3D multi-storied only shear walled or shear walled - framed structures using finite shear wall elements assumed ideal elasto - plastic material are developed. The collapse load of the system subjected to factored constant gravity loads and proportionally increasing lateral loads is calculated with a method of load increments. The shape functions over the element are determined as a cubic variation along the story height and a linear variation in horizontal direction because of the rigid behavior of the floor slab. In case shear walls are chosen as only one element in every floor, correct solutions are obtained by using this developed element. Because of the rigid behavior of the floor slabs, the number of unknowns are reduced substantially. While in framed structures, classical plastic hinge hypothesis is used, in nodes of shear wall elements when vertical deformation parameter is exceeded ${\varepsilon}_e$, this node is accepted as a plastic node. While the system is calculated with matrix displacement method, for determination of collapse safety, plastic displacements and plastic deformations are taken as additional unknowns. Rows and columns are added to the system stiffness matrix for additional unknowns.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.5
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• pp.82-89
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• 1995

The three-dimensional fluid motion through the intake port and cylinder of a single DOHC SI engine was investigated with a commercial computational fluid dynamics simulation program, STAR-CD. This domain includes the intake port, intake valves and combustion chamber. Steady induction port flows for various valve lifts have been simulated for an actual engine configuration. The geometry was obtained by direct interface with a three-dimensional CAD software for complicated port and valve shape. The computational grid was generated using the commercial preprocessor ICEM CFD/CAE. Detailed procedures were presented on the generation of the geometry and the block-structured mesh. A standard k-${\varepsilon}$ turbulent model was applied to consider the complexity of the geometry and the fluid motion. The global flow patterns and the distributions of various quantities, such as pressure, velocity magnitude around the valve seat etc., were examined. The computational results, such as mass flow rate, discharge coefficient etc., for various valve lifts were compard with the experimental results and the computational results were found in good agreement with the experiment.