• Journal of Korean Society for Atmospheric Environment
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• v.19 no.4
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• pp.377-386
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• 2003

In order to develop a confident sampling technique, we designed and constructed a 6-port manifold MFC sampling system for collecting gaseous pollutants in air. Using this instrumentation, we tested the performance criteria of MFC system in terms of: (1) flow rate; (2) MFC-to-MFC variability; (3) tube-to-tube variability; and (4) time. It was interesting to find that the later two factors did not show any significant variations, while the former two show substantially large variations. However, as most of those variabilities are consistent enough to form systematic patterns, we were able to explain the occurrence patterns of all those MFC biases in terms of those four major variables. The overall results of our experiment suggest that one needs to use correction factor for each MFC unit under a given flow rate to maintain optimal accuracy and precision for sampling of those pollutants.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.4
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• pp.507-514
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• 2012

The present study is the analyses of what has been attempted and what was understood in terms of improving the regression rate and enlarging the basic understanding of internal flow dynamics. The first part is mainly intended to assess the role of helical grain configuration in the regression rate inside the hybrid rocket motor. To improve the regression rate, a combination of swirl (which is an active method) and helical grain (which is a passive method) was adopted. The second part is devoted to the internal flow dynamics of hybrid rocket combustion. A large eddy simulation was also performed with an objective of understanding the origin of isolated surface roughness patterns seen in several recent experiments. Several turbulent statistics and correlations indicate that the wall injection drastically changes the characteristics of the near-wall turbulence. Contours of instantaneous streamwise velocity in the plane close to the wall clearly show that the structural feature has been significantly altered by the application of wall injection, which is reminiscent of the isolated roughness patterns found in several experiments.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.3
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• pp.371-380
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• 1998

The flow patterns and dynamic properties of ship's propulsion mechanism of two-stage Weis-Fogh type are studied by the discrete vortex method. In order to study the effects of the interaction of the two wings two cases of the phase differences of the wing's motion are considered the same phase and the reverse phase. The flow patterns by simulations correspond to the photographs obtained by flow visualization and flowfield of the propulsion mechanism which is unsteady and complex is clearly visualized by numerical simulations. The time histories of the thrust an the drag coefficients on the wings are also calculated and the effects of the interaction of the two wings are numerically clarified.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.2
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• pp.103-114
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• 2001

During a compression molding process of Unidirectional Fiber Reinforced Plastic Composites, control of filling patterns in mold and distribution of fiber is needed to predict the effects of molding parameters on the flow characteristics. To obtain an excellent product and decide optimum molding conditions, it is important to know the relationship between molding conditions and viscosity. In this study, the anisotropic viscosity of the Unidirectional Fiber Reinforced Plastic Composites is measured by using the parallel plastometer. The model for flow state has been simulated by using the viscosity. The composites is treated as an incompressible New-tonian fluid. The effects of longitudinal/transverse viscosity ration A and slip parameter $\alpha$ on buldging phenomenon and mold filling patterns, are also discussed.

• Journal of Mechanical Science and Technology
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• v.18 no.10
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• pp.1869-1879
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• 2004

The present study has numerically investigated two-dimensional flow over three circular cylinders in an equidistant side-by-side arrangement at a low Reynolds number. For the study, numerical simulations are performed, using the immersed boundary method, in the range of g* < 5 at Re= 100, where g* is the spacing between two adjacent cylinder surfaces divided by the cylinder diameter. Results show that the flow characteristics significantly depend on the gap spacing and a total of five kinds of wake patterns are observed over the range: modulation-synchronized (g* (equation omitted) 2), inphase-synchronized (g* (equation omitted) 1.5) , flip-flopping (0.3 < g* (equation omitted) 1.2) , deflected (g* (equation omitted) 0.3), and single bluff-body patterns (g* < 0.3). Moreover, the parallel and symmetric modes are also observed depending on g* in the regime of the flip-flopping pattern. The corresponding flow fields and statistics are presented to verify the observations.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.1014-1021
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• 2002

Analysis of two-dimensional secondary flows given by an oscillatory motion of a liquid with a free surface in a rectangular container subject to a linear reciprocating force is performed by numerical and experimental methods. FVM is used for the numerical computation of the two-dimensional flows. We considered the effects of the free-surface properties such as the surface tension and the dilatational viscosity. The boundary-layer analysis as well as an experiment is used in establishing the free surface properties. The secondary flow patterns are visualized by a laser sheet. It is shown that the secondary flow patterns predicted by the numerical methods are in good agreement with the experimental results.

• The Journal of the Society of Korean Medicine Diagnostics
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• v.16 no.1
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• pp.19-26
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• 2012

Objectives The aim of this study is to develop a cardiovascular simulator that can reproduce blood pressure pulse and blood flow similar to those of the human body. Methods In order to design a system similar to the human cardiovascular system, the required performances were determined by investigating the hemodynamic characteristics of the heart and the arterial system. Main organ to be imitated is heart in simulator. The rest of the system was minimally designed. Also, a blood pressure and blood flow measurement system was developed for measuring the results. Results The developed system showed blood pressure pulse at similar range of the human aorta. The result waveform include primary wave caused by ventricular systole except reflected wave. Conclusions The blood pressure and blow flow patterns were replicated by the simulator. These patterns were similar to those of the human body. The system will play an important role in studying pulse diagnostics.

• Journal of the Semiconductor & Display Technology
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• v.22 no.4
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• pp.1-6
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• 2023

In CO₂ laser surface machining of plastic films in modern display manufacturing, scattering of fume particles could be a major source of well-recognized film surface contamination. This computational fluid dynamics research investigates the suction air flow patterns over a film surface as well as the dispersion of micron-sized fume particles with low-Reynolds number particle drag model. The numerical results show the recirculatory flow patterns near laser machining point on film surface and also over the surface of vertical suction slot, which may hinder the efficient removal of fume particles from film surface. The dispersion characteristics of fume particles with various particle size have been tested systematically under different levels of suction flow intensity. It is found that suction removal efficiency of fume particles heavily depends on the particle size in highly nonlinear manners and a higher degree of suction does not always results in more efficient particle removal.

• 한국태양에너지학회:학술대회논문집
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• 2009.04a
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• pp.162-169
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• 2009

In summer electrical energy is consumed in very high rate. It is used to operate conventional air conditioning system. Hot and humid air can germinate mould spores, encourage ill health, and create physiological stress (discomfort). Dehumidifier solar cooling effect is the one alternative solution saving electrical energy. We use surplus heat energy in the summer, to get cooling effect and then to get human reach to comfort condition. These devices have two system, dehumidifier and regeneration system. This paper will be focus in dehumidifier system. Dehumidifier system use for absorbing moisture in the air and decreasing air temperature. When the liquid desiccant as strong solution contact with the vapor air in the packed tower, it works. The heat and mass transfer performances of flow pattern in the packed tower of dehumidifier are analyzed and compared in detail. In this experiment was introduced, the flow patterns are parallel flow and counter flow. The performance of these flow patterns will calculate from air side. Which is the best flow pattern that gave huge mass transfer rate? The proposed dehumidifier flow pattern will be helpful in the design and optimization of the dehumidifier solar cooling system.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.4
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• pp.833-846
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• 1988

Two-phase flow heat transfer phenomena with flash evaporation inside a vertical tube were studied experimentally. Void fractions were measured using electrical probes, and the flow patterns were identified from the output voltage signal itself. The flow pattern as well as the beat transfer rates were changing along the axial distance from the tube inlet with the system pressure. As the pressure inside the tube decreases with fixed inlet temperature, the overall heat transfer coefficient through the tube wall and the boiling heat transfer coefficient inside the tube increase whereas the condensation heat transfer coefficient outside the tube decreases. The boiling heat transfer coefficient inside the tube measured by the experiments appeared to be somewhat larger than the value obtained from the Chen's correlation. Also, the flow patterns identified from present experiments are at the larger quality region of the low pattern map based on the transition criteria of Mishima and Ishii. This may be due to the non-equilibrium flashing phenomenon occurred at the nozzle exit and the tube inlet ; this also implies that the flow pattern of the two-phase flow depends strongly on the inlet conditions.