• Journal of the Korean Society of Visualization
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• v.1 no.1
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• pp.82-91
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• 2003

The study of swirl flow has been of technical and scientific interest because it has an internal recirculation field and its tangential velocity is related to the curvature of the streamline. The fluid flow for ducts or elbows of an internal engine has been much studied through numerical methods and experiments, but studies about swirl flow has been insufficient. Using the PIV (Particle Image Velocimetry) method, this study found the time-mean velocity distribution, time-mean turbulent intensity, with swirl and without swirl flow for Re=10,000, 15,000, 20,000, and 25,000 along longitudinal sections and the results appear to be physically reasonable. In addition, axial velocity distribution is compared with that of Jeong's, Kodadadi's and Murakami's. It was found that the highest velocity of swirl and non-swirl flow occurs in the opposite position at the center of a round tube, $\phi$=45$^{\circ}$

• Journal of the Korean Society of Visualization
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• v.7 no.1
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• pp.21-28
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• 2009

The study of swirling flow is of technical and scientific interest because it has an internal recirculation field, and its tangential velocity is related to the curvature of streamline. The fluid flow for tubes and elbow of heat exchangers has been studied largely through experiments and numerical methods, but studies about swirling flow have been insufficient. Using the particle image velocimetry(PTV) method, this study found the time averaged velocity distribution with swirl and without swirl along longitude sections and the results appear to be physically reasonable. In addition, streamwise mean velocity distribution was compares with that of other. Furthermore, other experimental investigation was performed to study the characteristics of turbulent water flow in a horizontal circular tube by using liquid crystal. 2D PIV technique is employed for velocity measurement and liquid crystal is used for heat transfer experiments in water. Temperature visualization was made quantitatively by calibrating the colour of the liquid crystal versus temperature using various approaches.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.5
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• pp.220-230
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• 2017

In this study we apply and compare a variety of numerical methods for calculating residence time distribution in decay tanks, a major design component in the for reducing N-16 radioactivity. Our research group has used a streamlined method using user-defined particle numbers. However, this streamlined method has several problems, including low exiting particle ratios, particle diminishing, and unphysical time distribution, among others. We utilize three numerical methods to establish residence time and time distribution (streamlined, discrete phase method [DPM], and user defined scalar [UDS]) and subsequently compare the averaged results of each. The three tests demonstrate the flow features within the decay tanks, which are then numerically simulated to enable comparison. We conclude that although each simulation predicts similar time averages, the UDS methodology provides a smoother time distribution and tracer contour plots at specific times.

• Korean Chemical Engineering Research
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• v.48 no.4
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• pp.450-456
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• 2010

This study was conducted in order to design a piston, part of a shock absorber, and the findings after examining the features of the velocity distribution and the static pressure distribution of oil on a low-velocity piston are as follow. The compression speed of oil passing through an 0.9 mm orifice was 0.0156~0.0642 m/s, and the velocity vector of the velocity distribution and the static pressure distribution had a greater tendency to rotate when the velocity increased. In case of the velocity vector of the velocity distribution and the static pressure distribution with an 0.8mm orifice, the speed changed secondarily, the second pressure-drop was observed and as for the distribution of the streamline around the orifice, a vortex was produced around the center. As for the velocity distribution of oil passing from the compression cylinder to the compact pipe, the velocity was greater in orifice of small diameter. Also, the greater the pressure difference was between the compression cylinder and the compact cylinder, the greater the force it was upon the piston.

• Journal of ILASS-Korea
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• v.1 no.3
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• pp.37-50
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• 1996

Computational fluid dynamics was used to optimize an A/C duct. Three dimensional flow analysis in an automotive A/C duct was performed computationally using various turbulence models and compared numerical predictions such as outlet flow split, surface pressure distribution along the duct to experimental data. Additionally, we studied the effect of location variation of 2nd branch on exit flow ratio and could find optimal location of 2nd branch. The design of an A/C duct was modeled and calculated to enhance the airflow distribution in each outlet using the STAR-CD computational fluid dynamics software. In results, modified $k-\varepsilon$ turbulence model allows a successful prediction of static pressure distribution particulary at around strong curvature but little improvement flow split. In the future, adoption of CFD to design an A/C duct with modified $k-\varepsilon$ model will bring benefits of producing more accurate prediction, and also give designers more detail information much more than now.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.37-42
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• 2001

A computerized axial flow fan design system is developed with the capabilities for predicting the aerodynamic performance and the noise characteristics of fan. In the present study, the basic fan blading design is made by combining vortex distribution scheme with camber line design, airfoil selection, blade thickness distribution and stacking of blade elements. With the designed fan blade geometry, the through-flow field and the performance of fan are analyzed by using the streamline curvature computing scheme with spanwise total pressure loss and flow deviation models. Fan noise is assumed to be generated due to the pressure fluctuation induced by wake vortices of fan blades and to radiate as dipole distribution. The vortex-induced fluctuating pressure on blade surface is calculated by combining thin airfoil theory and the predicted flow field data. The predicted performances, sound pressure level and noise directivity patterns of fan by the present method are favorably compared with the test data of actual fans. Furthermore, the present method is shown to be very useful in designing the blade geometry of new fan and optimizing design variables of the fan to achieve higher efficiency and lower noise level.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.676-683
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• 2003

A laboratory experiment using artificial fracture rocks was used to understand the 3-dimensional dispersion of a tracer and the mixing process in a fractured network. In this experiment, 12cm polystyrene foam cubes with two electrodes for monitoring electric conductivity (EC) were used as artificial fractured rocks. Distilled water with 0.5mS/m was used as a tracer in water with 35mS/m and the difference of EC between the tracer and the water was monitored by a multipoint simultaneous measurement system of electrical resistance. The results showed that even if the fracture arrangement pattern was not straight in the direction of the flow, the tracer did not diffuse along individual fractures and an oval tracer plume, which was the distribution of tracer concentrations, tended to be form in the direction of the flow. The vertical cross section of the tracer distribution showed small diffusivity in the vertical direction. The calculated total tracer volume passing through each measurement point in the horizontal cross section showed while that the solute passed through measurement points near the direction of hydraulic gradient and in other directions, the passed tracer volumes were small. Using Peclet number as a criterion, it was found that the mass distribution at the fracture intersection was controlled in the stage of transition between the complete mixing model and the streamline routing model.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.4 no.2
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• pp.180-188
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• 1994

This study was designed to investigate qualitatively whether respirators now being used in workplaces tit workers iflfaces well or not. Leak sites were determined after exposing the subjects to fluorescent aerosol and were analyzed by gender, brand and manufacturing nation. The results were as follows ; 1. Among those leak sites which were classified into four areas(nose, cheek, lip and chin), test aerosol was mostly deposited on the nose and the cheek areas. 2. The mean number of leak sites observed from the female subjects were 2.3 while the number were 2.2 from the male subjects. The most frequently observed leak site was nose and followed by chin, lip and cheek in descending order of frequency. 3. Among different brands of respirators, different leak sites were observed. Test subjects wearing the Sand N brands were more heavily exposed than those of wearing the D and M brands. 4. No significant difference of the number of leak sites were found between Korean-made and American-made masks. However, the most frequent leak site observed for the Korean-made ones was the nose area while it was the chin area for the American-made ones. 5. Analyses of 97 leak sites by shape showed that 27(27.8%) were point types, 54(55.7%) diffuse types and 16(16.5%) streamline types. 6. Test subjects indicated that the facepieces of Korean-made respirators were harder and smaller in size than those of American-made one. The most comfortable respirator selected was the respirator by the N Co. and the most uncomfortable one was the respirator by the D Co. This study suggests that many half-mask respirators now being used in the workplaces may not fit to workers well. Therefore, when selecting respirators, employers are advised to test respirators if they fit to workers well. And manufacturers are recommended to produce effective and comfortable respirators tested qualitatively and quantitatively not only in the laboratory but also in the field.

• Journal of the Korean Society of Tobacco Science
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• v.18 no.1
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• pp.12-20
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• 1996

The spermatogenesis and chromosome number were investigated in the pupal testes of Helicouerpa assulta Guenee by light microscopy. During the spermatogenesis, each bundle of P8(256) sperms developed by 6 mitotic and 2 meiotic spermatogonial divisions. From the early stage of spermatogenesis, it was distinguishable between two kinds of sperm differentiation, eupyrene and apyrene spermatogenesis, which are characteristic in Lepidoptera, by the differences in nuclear shape and cell distribution in immature spermatocyst. Through the followed spermiogenesis, the spermatocysts were developed into two kinds of mature cyst, a streamline-shaped eupyrene cyst with nucleated sperms of thready head or a long spindle-shaped apyrene cyst with anucleated sperms of cylindrical head. As the results off chromosomal analysis at metaphase of the spermatogonial mitosis and spermatocytic meiosis, the chromosome number were 2n=6a/n=31, respectively, and no variation between individuals.

• Tribology and Lubricants
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• v.17 no.5
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• pp.391-398
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• 2001

Two dimensional slow viscous flow around two counter-rotating equal cylinders is investigated based on Stokes'approximation. An exact formal expression of the stream function is obtained by using the bipolar cylinder coordinates and Fourier series expansion. From the stream function obtained, the streamline patterns around the cylinders are shown and the pressure distribution in the flow field is determined. By integrating the stress distributions on the cylinder, the force and the moment exerted on the cylinder are calculated. The flow rate through the gap between the two cylinders is also determined as the distance between two cylinders varies. Special attention is directed to the case of very small distance between two cylinders concerned with the lubrication theory and the minimum pressure is calculated to explain a possible cavitation.