• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.129-134
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• 2009

In the present study, the characteristic of flow distribution in the channel of a plate heat exchanger is investigated numerically. In order to accomplish the efficient and fast analyses of the flow characteristics in the channel, a semi-microscopic analysis has been performed using a porous media model. For semi-microscopic analysis using porous media, the flow resistance coefficients are obtained through the result of pressure drop in the experimental data. The results showed that the variation of mass flow rate, geometry and chevron angle strongly depend on the flow distribution in the channel. Particularly, the chevron angle is most important factor for uniform flow distribution.

• 한국표면공학회지
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• 제36권1호
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• pp.69-73
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• 2003

The atmospheric pressure plasma is regarded as an effective method for surface treatments because it can reduce the period of process and doesn't need expensive vacuum apparatus. The performance of non-transferred plasma torches is significantly depended on jet flow characteristics out of the nozzle. In order to produce the high performance of a torch, the maximum discharge velocity near an annular gap in the torch should be maintained. Also, the compulsory swirl is being produced to gain the shape that can concentrate the plasma at the center of gas flow. In this work, the distribution of gas flow that goes out to atmosphere through a plenum chamber and nozzle is analyzed to evaluate the performance of atmospheric pressure plasma torch which can present the optimum design of the torch. Numerical analysis is carried out with various angles of an inlet flow velocity. Especially, three-dimensional model of the torch is investigated to estimate swirl effect. We also investigate the stabilization of plasma distribution. For analyzing the swirl in the plenum chamber and the flow distribution, FVM (finite volume method) and SIMPLE algorithm are used for solving the governing equations. The standard k-model is used for simulating the turbulence.

• Korea-Australia Rheology Journal
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• 제15권1호
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• pp.35-41
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• 2003

It is expected that particle size distribution of any portion obtained through screening, is of more uniform than that of the original mixture, typically following such as log-normal, Rosin-Rammler distributions and so on. In this study, therefore, a new relation between parameters of the uniform distribution and flow characteristics of the coarse particle suspensions is derived based on the continuous polydisperse model (Ookawara and Ogawa, 2002b), which is derived from the discrete polydisperse model (Ookawara and Ogawa,2002a). The derived model equation predicts a linear increase of viscosity with shear rate, viz., dilutant flow characteristics. Further, the increase of viscosity is expected to be proportional to the square of volume fraction of particles, and to show the linear dependency on density and average diameter of particles. It is also shown that the uniform distribution model includes additional term that expresses the effect of distribution width. For verification of the model, the experimental results of Clarke (1967) are cited as well as in our previous work for the monodisperse model (Ookawara and Ogawa,2000) since most parameters were varied independently in his work. It is suggested that the newly introduced term expands the applicable range compared with the monodisperse model.

• 산업경영시스템학회지
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• 제41권2호
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• pp.95-104
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• 2018

Using network betweenness centrality we attempt to analyze the characteristics of Seoul metropolitan subway lines. Betweenness centrality highlights the importance of a node as a transfer point between any pairs of nodes. This 'transfer' characteristic is obviously of paramount importance in transit systems. For betweenness centrality, both traditional betweenness centrality measure and weighted betweenness centrality measure which uses monthly passenger flow amount between two stations are used. By comparing traditional and weighted betweenness centrality measures of lines characteristics of passenger flow can be identified. We also investigated factors which affect betweenness centrality. It is the number of passenger who get on or get off that significantly affects betweenness centrality measures. Through correlation analysis of the number of passenger and betweenness centrality, it is found out that Seoul metropolitan subway system is well designed in terms of regional distribution of population. Four measures are proposed which represent the passenger flow characteristics. It is shown they do not follow Power-law distribution, which means passenger flow is relatively evenly distributed among stations. It has been shown that the passenger flow characteristics of subway networks in other foreign cities such as Beijing, Boston and San Franciso do follow power-law distribution, that is, pretty much biased passenger flow traffic characteristics. In this study we have also tried to answer why passenger traffic flow of Seoul metropolitan subway network is more homogeneous compared to that of Beijing.

• 한국자동차공학회논문집
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• 제6권4호
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• pp.108-120
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• 1998

A theoretical study of three-dimensional unsteady compressible non-reacting flow inside double flow of monolith catalytic converter system attached to 6-cylinder engine was performed for the achievement of performance improvement, reduction of light-off time, and longer service life by improving the flow distribution of pulsating exhaust gases. The differences between unsteady and steady-state flow were evaluated through the numerical computations. To obtains the boundary conditions to a numerical analysis, one dimensional non-steady gas dynamic calculation was also performed by using the method of characteristics in intake and exhaust system. Studies indicate that unsteady representation is necessary because pulsation of gas velocity may affect gas flow uniformity within the monolith. The simulation results also show that the level of flow maldistribution in the monolith heavily depends on curvature and angles of separation streamline of mixing pipe that homogenizes the exhaust gas from individual cylinders. It is also found that on dual flow converter systems, there is severe interactions of each pulsating exhaust gas flow and the length of mixing pipe and junction geometry influence greatly on the degree of flow distribution.

• 한국기계가공학회지
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• 제10권4호
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• pp.115-120
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• 2011

A ribbed tube consumes more power to transport the fluid by comparing with flat one. After the tangential velocity component occurs, its contact area with the ribbed tube becomes large and it enables the effective energy transportation. The flow characteristics vary according to the geometry of tube rib. This study aims to investigate the flow characteristics of fluids working at Reynolds numbers of 20,000, 40,000, 60,000 and 80,000 with the air at $15^{\circ}C$ in the ribbed test tube high 1mm and wide 8.48mm. As the flow characteristics are included with the states of fully developed hydrodynamical region, axial velocity vector distribution and non-dimensional velocity distribution, they are shown with the physical validity.

• 설비공학논문집
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• 제10권1호
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• pp.1-10
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• 1998

A header is the device that makes uniform flow distribution in all branches from header of heat exchangers, pipe burner or chemical equipments. In this study, experimental tests have been performed in order to investigate the flow distribution characteristics in a straight header and tapered header which have 6 and 11 glass pipe branches. The experimental equipment consists of a water circulation system where the fluid velocity in each glass pipe is measured by Ar-ion LDV system. From the experiments and the theoretical equation, it could be recommended that tapered header should be determined so that its internal velocities inside the header become uniform according to taper of the header and number of attached branches for uniform flow distribution in energy systems.

• Nuclear Engineering and Technology
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• 제54권7호
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• pp.2720-2727
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• 2022

The Generation IV Lead-cooled fast reactor (LFR) take the liquid lead or lead-bismuth eutectic alloy (LBE) as the coolant of the primary cooling circuit. Combined with the natural characteristics of lead alloy and the design features of LFR, the system is the simplest and the number of equipment is the least, which reflects the inherent safety characteristics of LFR. The nuclear main coolant pump (MCP) is the only power component and the only rotating component in the primary circuit of the reactor, so the various operating characteristics of the MCP are directly related to the safety of the nuclear reactor. In this paper, various working conditions that may occur in the normal rotation (positive rotating) of the MCP and the corresponding internal flow characteristics are analyzed and studied, including the normal pump condition, the positive-flow braking condition and the negative-flow braking condition. Since the corrosiveness of LBE is proportional to the fluid velocity, the distribution of flow velocity in the pump channel will be the focus of this study. It is found that under the normal pump condition and positive-flow braking conditions, the high velocity region of the impeller domain appears at the inlet and outlet of the blade. At the same radius, the pressure surface is lower than the back surface, and with the increase of flow rate, the flow separation phenomenon is obvious, and the turbulent kinetic energy distribution in impeller and diffuser domain shows obvious near-wall property. Under the negative-flow braking condition, there is obvious flow separation in the impeller channel.

• 대한조선학회논문집
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• 제44권3호
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• pp.228-237
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• 2007

The flow characteristics around a horn-type rudder behind an operating propeller of a high-speed large container carrier are studied through a numerical method in fully wetted and cavitating flow conditions. The computations are carried out in a small scale ratio of 10.00(gap space=5mm) to consider the gap effects. The Reynolds averaged Navier-Stokes equation for a mixed fluid and vapor transport equation applying cavitation model are solved. The axisymmetry body-force distribution technique is utilized to simulate the flow behind an operating propeller. The gap flow, the three-dimensional flow separation, and the cavitation are the flow characteristics of a horn-type rudder. The pattern of three-dimensional flow separation is analyzed utilizing a topological rule. The various cavity positions predicted by CFD were shown to be very similar to rudder erosion positions in real ship rudder. The effect of a preventing cavitation device, a horizontal guide plate, is also investigated.

• 대한기계학회논문집B
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• 제22권2호
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• pp.139-152
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• 1998

In the present study, the flow characteristics of developing laminar oscillatory flows in a square -sectional 180 deg. curved duct are investigated experimentally. The experimental study using air in a square-sectional 180 deg. curved duct is carried out to measure velocity distributions with a data acquisition and LDV (Laser Doppler Velocimetry) processing system. In this system, Rotating Machinery Resolver (RMR) and PHASE program are used to obtain the results of unsteady flows. The major flow characteristics of developing oscillatory flows are found by analyzing velocity curves, mean velocity profiles, time-averaged velocity distribution of secondary flow, wall shear stress distributions, and entrance lengths. In a lower dimensionless angular frequency, the axial velocity distribution of laminar oscillatory flow in a curved duct shows a convex shape in a central part and axial symmetry. The maximum value of wall shear stress in a lower dimensionless angular frequency is located in an outside wall, but according to increasing the dimensionless angular frequency, the maximum of wall shear stress is moved to inner wall. The entrance lengths of laminar oscillatory flows in a square-sectional 180 deg. curved duct is obtained to 90 deg. of bended angle of duct in this experimental conditions.