• Journal of the Korean Society of Visualization
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• v.4 no.2
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• pp.76-80
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• 2006

The data for friction factor of the pipe correlated by Reynolds number and relative roughness have been reported well as a Moody chart. However, the results for corrugated shapes have been not investigated sufficiently. In this research, therefore, the pressure drop and friction factor are obtained. Flexible metal tubes with corrugations for the measurement are made of stainless steel plates. The kinds of tubes for the measurement are 5 annular types and helical types. The pressure drop & the velocity of the flow are obtained by micromanometer & digital pressure sensor, supplying dry air at several steps. Then the pressure drop is calculated for each tube, using the obtained data. The result shows that the pressure drop is strongly influenced by the viscous dissipation of kinetic energy due to the circulation of flows, rather than a viscous friction loss. The pressure drop increased consistently as the Reynolds number increases.

• Journal of Biosystems Engineering
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• v.32 no.6
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• pp.389-394
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• 2007

The power output of the stirling engine is influenced by the regenerator effectiveness. The regenerator effectiveness is influenced by heat transfer and flow friction loss of the regenerator matrix. In this paper, in order to provide basic data for the design of the regenerator matrix, characteristics of working fluid velocities were investigated by a packed method of matrix in the oscillating flow as the same condition of operation in a Stirling engine. As matrices, two different wire screens were used. The results are summarized as follows; 1. When a regenerator is not filled with any wire screen, working fluid velocity of the oscillating flow shows 1.3 times faster than that of one directional flow. 2. When a regenerator is filled with the wire screen of No.50, working fluid velocity of the oscillating flow reveals 2.5 times faster than that of one directional flow. 3. When a regenerator is filled with the wire screen of No. 100, working fluid velocity of the oscillating flow shows 2 times faster than that of one directional flow, regardless of the number of packed wire screens. 4. Working fluid velocity is decreased wire the increase in number of meshes and packed wire screens.

• Journal of computational fluids engineering
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• v.17 no.2
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• pp.1-10
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• 2012

This paper presents the numerical simulation results of heat transfer and friction loss for a rotating two-pass duct with the airfoil-guide vanes in the turning region. The Kriging model is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of flow field and heat transfer with shear stress transport turbulent model. To improve the heat transfer performance, angle and location of the airfoil-guide vanes have been selected as design variables. The optimization problem has been defined as a minimization of the objective function, which is defined as a linear combination of heat transfer related term and friction loss related term with a weight factor. The airfoil-guide vanes in the turning region keep the high level of heat transfer while the friction loss has a low value. By comparing the presence or absence of airfoil-guide vanes, it is shown that the airfoil-guide vanes exhibited the best heat transfer performance to improve the blade cooling except the first passage.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.1
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• pp.37-44
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• 2012

This paper describes energy loss in a pipe line of refuse collecting system. Analysis of energy loss in a pipe line is the decisive factor in a design of refuse collecting system. Using the results of energy loss analysis, we can determine the power of turbo-blower. The flow characteristics of the pipe line with refuse bags were analyzed by three-dimensional CFD. The refuse bag is modeled by using the shape obtained from profile measurement. Friction factors were calculated with changing the refuse bag size, mixing ratio and Reynolds number. And drag coefficients were calculated using the CFD results. From the results we can calculate energy loss in a pipe line of refuse collecting system and predict the capacity of turbo-blower.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.4
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• pp.421-428
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• 2007

Many engineering problems on the pipeline flow use continuity, energy, friction loss head equation. To calculate friction loss head in a pipeline, Darcy-Weisbach and many average velocity equations can be used and Hazen-Williams equation is used frequently in the pipe network for the water supply systems. Darcy-Weisbach equation is a general one acquired from applying Bernoulli's equation in the pipeline flow and Hazen-Williams equation is a experimental one in case that pipe velocity is below 3m/sec and pipe diameter is over 50mm. In this study, comparing Darcy-Weisbach with Hazen-Williams equation, relation f and C that are expressed as roughness coefficients of those equations is explained. Next, head losses calculated from using those equations are compared and those are applied in realistic pipelines. Comparing f with C, the f is decreasing linearly according to increase of the Reynolds number Re and increasing in case the C is decreasing. additionally, the C is increasing up to a point and then is decreasing according to increase of the Re. Next, the C is increasing and Re's range for increase of the C lengthens in case of decreasing of the relative roughness ${\varepsilon}/d$. Comparing head losses acquired from the two equations, head loss appears large in case that the C is decreasing and the ${\varepsilon}/d$ is increasing. additionally, Head loss calculated by the Darcy-Weisbach equation varies larger than one by Hazen-Williams equation in regard of the Re. Next, change aspect of head loss acquired by the C is distinguished more clearly than the one by the ${\varepsilon}/d$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.5 s.236
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• pp.545-553
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• 2005

In the present study, The characteristics of developing steady laminar flows of a straight duct connected to a $180^{\circ}$ curved duct were examined In the entrance region through experimental measurement. Flow characteristics such as shear stress distributions, pressure distributions and friction coefficient experimentally in a square cross-sectional straight duct by using the PIV system. For the PIV measurement by particles produced from mosquito coils particles. The experimental data were obtained at 9 points dividing the test sections by 400mm. Experimental results can be summarized as follows. Critical Reynolds number, $Re_{cr}$ which indicates transition from laminar steady flow to transition steady flow was 2,150. Shear stress per unit length on the wall was stronger than that in the fully developed flow region. This was attributed to the fact that shear stress and pressure loss in the curvature of a duct were increased. Pressure distributions were gradually decreased irrespective of Reynolds number In the whole test section. This trends were in a good agreement with the reference results. Pipe friction coefficient in the steady state flow region was calculate from method of least squares. The co-relationship between fiction coefficient and Reynolds number was established as follow; ${\lambda}=56/Re$.

• Journal of the Korean Society of Mechanical Technology
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• v.13 no.4
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• pp.1-7
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• 2011

The paper concerns numerical study of fully developed laminar flow of a Newtonian water and non-Newtonian fluids, 0.2% aqueous of sodium carboxymethyl cellulose(CMC) solution in eccentric annuli with combined bulk axial flow and inner cylinder rotation. Pressure losses and skin friction coefficients have been measured when the inner cylinder rotates at the speed of 0~200 rpm. A numerical analysis considered mainly the effects of annular eccentricity and inner cylinder rotation. The present analysis has demonstrated the importance of the drill pipe rotation and eccentricity. In eccentricity of 0.7 of a Newtonian water, the flow field is recirculation dominated and unexpected behavior is observed. it generates a strong rotation directed layer, that two opposing effects act to create two local peaks of the axial velocity. The influences of rotation, radius ratio and working fluid on the annular flow field are investigated.

• Nuclear Engineering and Technology
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• v.56 no.8
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• pp.3435-3449
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• 2024

Considering that system analysis codes are used for the evaluation of the performance of Passive Safety Systems (PSSs), it is important to investigate the capability of the system analysis code to reliably predict the heat transfer and natural circulation flow, which are the main phenomena governing the performance of a PSS. Since MARS-KS has been widely validated for heat transfer models, this study focuses on evaluating its capability to predict the single and two-phase pressure drops and natural circulation flow. The straight pipe simulation results indicate that the pressure drop predictions are reliable within ±5 % error margin for the single-phase flow and the errors of pressure drop up to - 30 % for the two-phase flow. Through single-phase natural circulation flow analysis, it is concluded that the use of the appropriate K-factor modeling based on the flow regimes is important since the natural circulation flow rate in MARS-KS is mainly affected by the form loss factor modeling. With two-phase natural circulation flow analysis, this study emphasizes the behavior of the system could change significantly depending on the two-phase wall friction and pressure loss modeling. With the analysis results, modeling considerations for the PSS performance evaluation with the system analysis codes are proposed.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.4
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• pp.447-458
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• 2009

Energy loss at manholes, often exceeding friction loss of pipes under surcharged flow, is considered as one of the major causes of inundation in urban areas. Therefore, it is necessary to analyze head loss at manholes, especially in case of surcharged flow. Hydraulic experiments were conducted with three cases. Case A is to test whether the shapes of the manholes influence head loss coefficients. Case B and C were proposed to further reduce head losses by improving the manhole hydraulic efficiency. In case B, the joining part of the pipe at both shapes of manholes is shifted from central part to side part. The test in case C is to check the average head loss coefficient by installing the side benching in square manhole, based on shifted joining part model. The average head loss coefficient for circular and square manhole on case A was 1.6. This did not show much difference of the head loss coefficients in spite of the discharge variation in this case. However, case B and C show large difference between head loss coefficients due to the strong oscillation of water surface and the horizontal swirl motion. The circular and square manholes in case B reduced the head loss by 30% and 6% than ones in case A, respectively. The average head loss coefficient for circular manhole in case B was 1.1. Case C reduced average loss coefficients of the square manhole in case A from 1.6 to 1.1. Accordingly, the circular manhole in case B and the square manhole in case C showed the effective way to reduce the head loss. These head loss coefficients could be available to apply to the urban sewer system with surcharged flow.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.11
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• pp.751-759
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• 2010

A newly developed type PCHE(Printed Circuit Heat Exchanger), which has a longitudinal corrugation flow channel, was fabricated using etching and diffusion bonding to evaluate its hydraulic performance. The pressure drop characteristics obtained from the experimental results are presented and the local friction factors associated with different hydraulic diameters and inclination angles are discussed. The results of a three-dimensional numerical simulation are presented, conducted using commercial CFD(Computational Fluid Dynamics) software at lower Reynolds number range. The numerical results were validated by experimental data obtained from helium gas experimental apparatus. The results of CFD prediction show fairly good agreement with the experimental data.