• Title/Summary/Keyword: flow channel

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Study on Two-Dimensional Laminar Flow through a Finned Channel (박막이 부착된 채널내의 2차원 층류유동장에 대한 연구)

  • Yoon Seok-Hyun;Jeong Jae-Tack
    • Journal of computational fluids engineering
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    • v.7 no.3
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    • pp.53-59
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    • 2002
  • A two-dimensional laminar flow through a channel with a pair of symmetric vertical fins is investigated. At far up- and down-stream from the fins, the plane Poiseuille flow exists in the channel. The Stokes flow for this channel is first investigated analytically and then the other laminar flows by numerical method. For analytic method, the method of eigen function expansion and collocation method are employed. In numerical solution for laminar flows, finite difference method(FDM) is used to obtain vorticity and stream function. From the results, the streamline patterns are shown and the additional pressure drop due to the attached fins and the force exerted on the fin are calculated. It is clear that the force depends on the length of fins and Reynolds number. When the Reynolds number exceeds a critical value, the flow becomes asymmetric. This critical Reynolds number Re/sub c/ depends on the length of the fins.

Flow Analysis of Reverse Flow in a Channel with High Angle of Attack (받음각이 큰 평판 채널 내의 역류 유동 해석)

  • Choi, Seung;Sohn, Chang-Hyun
    • Journal of the Korean Society of Visualization
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    • v.5 no.1
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    • pp.37-42
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    • 2007
  • Reverse flow occurs in a channel when there is an obstruction at the entry. However it has been shown recently that reverse flow can be realized without an obstruction, by staggering the sides of the channel and placing it at an angle of attack to the oncoming flow. In this study the latter flow is computationally investigated. Studies have been carried out for different widths (gap between the two walls forming the channel), and at an angle of attack of 30. The results have captured all the essential features of this complex phenomenon and show the time dependent pumping mechanism which leads to the occurrence of reverse flow.

A Study on Flow Characteristics according to Meandering Low Flow Channel Shape in the Compound Cross Section Typed Straight Channel (복단면인 직선수로 내 사행 저수로의 형태에 따른 흐름특성 연구)

  • Kim, Seonghwan;Choi, Gyewoon
    • Journal of Wetlands Research
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    • v.19 no.4
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    • pp.484-490
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    • 2017
  • In order to examine flow characteristics according to the shape of the meandering low flow channel in the compound cross section typed straight channel, we assumed the representative channel type in Korea and confirmed the validity of the 3D numerical simulation by carrying out the hydraulic model. Based on this study, numerical simulations were also conducted on other types of river channel. As a result of the numerical model test (using the velocity value measured by the water depth observation from the hydraulic model test), it was confirmed that the numerical simulation results are in good agreement with the numerical simulation results. As a result of analyzing the flow field according to the changes in the shape of the low flow channel, it was confirmed that the secondary flow examined in the previous studies occurred. Also, it was confirmed that the maximum flow velocity point moves according to the expansion cross sectional area of flow in high flow plain. Ultimately, it is thought that it is necessary to understand the position of the water impingement (which is an important factor in river design) and the extent of the impact because the change of the channel width affects the flow.

Numerical Study on Comparison of Serpentine and Parallel Flow Channel in High-temperature Proton Exchange Membrane Fuel Cells (고온형 고분자전해질형 연료전지에서의 사형 유로와 평행 유로 성능비교에 대한 수치해석적 연구)

  • AHN, SUNGHA;OH, KYEONGMIN;JU, HYUNCHUL
    • Transactions of the Korean hydrogen and new energy society
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    • v.29 no.1
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    • pp.41-55
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    • 2018
  • General polymer electrolyte fuel cell (PEMFC) operates at less than $80^{\circ}C$. Therefore liquid phase water resulting from electrochemical reaction accumulates and floods the cell which in turn increases the mass transfer loss. To prevent the flooding, it is common to employ serpentine flow channel, which can efficiently export liquid phase water to the outlet. The major drawback of utilizing serpentine flow channel is the large pressure drop that happens between the inlet and outlet. On the other hand, in the high temperature polymer electrolyte fuel cell (HT-PEMFC), since the operating temperature is 130 to $180^{\circ}C$, the generated water is in the state of gas, so the flooding phenomenon is not taken into consideration. In HT-PEMFCs parallel flow channel with lower pressure drop between the inlet and outlet is employed therefore, in order to circulate hydrogen and air in the cell less pumping power is required. In this study we analyzed HT-PEMFC's different flow channels by parallel computation using previously developed 3-D isothermal model. All the flow channels had an active area of $25cm^2$. Also, we numerically compared the performance of HT-PEMFC parallel flow channel with different manifold area and Rib interval against the original serpentine flow channel. Results of the analysis are shown in the form of three-dimensional contour polarization curves, flow characteristics in the channel, current density distribution in the Membrane, overpotential distribution in the catalyst layer, and hydrogen and oxygen concentration distribution. As a result, the performance of a real area fuel cell was predicted.

Analysis of Performance Characteristics by Inner Flow Path of Side Channel Type Ring Blower (사이드 채널형 링블로워의 임펠러 내부 유로에 따른 성능변화 분석)

  • Lee, Kyoung-Yong;Choi, Young-Seok;Jeong, Kyung-Ho;Park, Woon-Jean
    • The KSFM Journal of Fluid Machinery
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    • v.15 no.4
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    • pp.67-71
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    • 2012
  • This study analyzed performance changes by an inner flow path of impeller groove for side channel type ring blower using CFD. Two models have the same side channel and clearance while one has an inner flow path and the other doesn't. To analyze the performance change of a ring blower, overall performance and local flow field were analyzed. For the overall performance, pressure increase and impeller torque were checked under the design flow condition. Under the design flow condition, pressure increase was greater for the model with the inner flow path. The model with the inner flow path showed improved efficiency because the area subject to torque decreased due to the creation of inner flow path. To analyze local flow field, a section was created from the representative location of each impeller groove toward the direction of radius. Inner channel pressure distribution depending on the rotation direction shows that the model with the inner flow path has pressure equilibrium of working fluid through the inner flow path. Velocity distribution of inside impeller groove shows that flow field was coupled and appeared to form an inner wall where the flow field was stabilized.

Numerical study of dividing open-channel flows at bifurcation channel using TELEMAC-2D (TELEMAC-2D모형을 이용한 개수로 분류흐름에 대한 수치모의 연구)

  • Jung, Dae Jin;Jang, Chang-Lae;Jung, Kwansue
    • Journal of Korea Water Resources Association
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    • v.49 no.7
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    • pp.635-644
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    • 2016
  • This study investigates variation of flow characteristics due to variation of branch channel width and discharge ratio at bifurcation channel using 2D numerical model. The calculated result considering secondary flow is more accurate and stable than without considering one. The diversion flow rate ($Q_3/Q_1$) is reduced by flow stagnation effect according to the interaction of the secondary flow and flow separation zone in branch channel. The less upstream inflow or the lower upstream velocity, the bigger variation of diversion flow rate by changing branch channel width. At uniform downstream boundary condition, the rate of change in Froude number of downstream of main channel($Fr_2$)-diversion flow rate ($Q_3/Q_1$) relations is similar about -2.4843~-2.6675 when branch channel width ratio (b/B) is decreased. At uniform diversion flow rate ($Q_3/Q_1$) condition, the width of recirculation zone in branch channel is decreased when branch channel width ratio (b/B) is decreased. The less upstream inflow in the case of increasing branch channel width or the narrower branch channel width in the case of increasing upstream inflow, the bigger reduction ratio of recirculation zone width. At uniform inflow discharge ($Q_1$) condition, diversion flow rate, the width and length of recirculation zone in branch channel are decreased when branch channel width ratio (b/B) is decreased.

Numerical Analysis on Performance Characteristics of PEMFC with Parallel and Interdigitated Flow Channel (평행류와 Interdigitated 유로를 가진 교분자 전해질 연료전지(PEMFC)의 성능특성에 대한 수치해석)

  • Lee, Pil-Hyong;Cho, Son-Ah;Choi, Seong-Hun;Hwang, Sang-Soon
    • Journal of the Korean Electrochemical Society
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    • v.9 no.4
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    • pp.170-177
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    • 2006
  • Optimum design of flow channel in the separation plate of Proton Exchange Membrane Fuel Cell is very prerequisite to reduce concentration over potential at high current region and remove the water generated in cathode effectively. In this paper, fully 3 dimensional computational model which solves anode and cathode flow fields simultaneously is developed in order to compare the performance of fuel cell with parallel and interdigitated flow channels. Oxygen and water concentration and pressure drop are calculated and i-V performance characteristics are compared between flows with two flow channels. Results show that performance of fuel cell with interdigitated flow channel is hi민or than that with parallel flow channel at high current region because hydrogen and oxygen in interdigitated flow channel are transported to catalyst layer effectively due to strong convective transport through gas diffusion layer but pressure drop is larger than that in parallel flow channel. Therefore Trade-off between power gain and pressure loss should be considered in design of fuel cell with interdigitated flow channel.

Traffic Flow Estimation based Channel Assignment for Wireless Mesh Networks

  • Pak, Woo-Guil;Bahk, Sae-Woong
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.5 no.1
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    • pp.68-82
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    • 2011
  • Wireless mesh networks (WMNs) provide high-speed backbone networks without any wired cable. Many researchers have tried to increase network throughput by using multi-channel and multi-radio interfaces. A multi-radio multi-channel WMN requires channel assignment algorithm to decide the number of channels needed for each link. Since the channel assignment affects routing and interference directly, it is a critical component for enhancing network performance. However, the optimal channel assignment is known as a NP complete problem. For high performance, most of previous works assign channels in a centralized manner but they are limited in being applied for dynamic network environments. In this paper, we propose a simple flow estimation algorithm and a hybrid channel assignment algorithm. Our flow estimation algorithm obtains aggregated flow rate information between routers by packet sampling, thereby achieving high scalability. Our hybrid channel assignment algorithm initially assigns channels in a centralized manner first, and runs in a distributed manner to adjust channel assignment when notable traffic changes are detected. This approach provides high scalability and high performance compared with existing algorithms, and they are confirmed through extensive performance evaluations.

The study on heat transfer enhancement using indirect cooling system in the channel with heat source (간접냉각방식을 이용한 열원이 부착된 채널내의 열전달 촉진에 관한 연구)

  • 김광추;박만흥;윤준규
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.11 no.3
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    • pp.321-331
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    • 1999
  • A numerical study is carried out for increasing heat removal using indirect cooling system. Computation is performed for nine cases as variation of flow condition in the lower channel. As the result of this study, water is more effective than air at the same pressure loss in spite of the lower inlet velocity. In channel configuration, the vertical channel is more effective than horizontal channel because of the buoyancy effect. Under the condition that heat generation is the same, counter flow effectively decreases the temperature difference among blocks. Parallel flow is more effective than counter flow when average temperature of all blocks is considered. In the case of installing obstacles in the lower channel, it is desirable to install obstacles in the bottom of lower channel. Heat transfer rate increases as the height of obstacles increases.

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A Study of the Flow Phenomenon of Water in a Channel with Flat Plate Obstruction Geometry at the Entry

  • Khan, M.M.K.;Kabir, M.A.;Bhuiyan, M.A.
    • Journal of Mechanical Science and Technology
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    • v.17 no.6
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    • pp.879-887
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    • 2003
  • The flow in a parallel walled test channel, when obstructed with a geometry at the entrance, can be forward, reverse and stagnant depending on the position of the obstruction. This interesting flow phenomenon has potential benefit in the control of energy and various flows in the process industry In this experiment, the flat plate obstruction geometry was used as an obstruction at the entry of the test channel. The parameters that influence the flow inside and around the test channel were the gap (g) between the test channel and the obstruction geometry, the length (L) of the test channel and the Reynolds number (Re). The effect of the gap to channel width ratio (g/w) on the magnitude of the velocity ratio (V$\_$i/ / V$\_$o/ : velocity inside/ velocity outside the test channel) was investigated for a range of Reynolds numbers. The maximum reverse flow observed was nearly 20% to 60% of the outside velocity for Reynolds number ranging from 1000 to 9000 at g/w ratio of 1.5. The maximum forward velocity inside the test channel was found 80% of the outside velocity at higher g/w ratio of 8. The effect of the test channel length on the velocity ratio was investigated for different g/w ratios and a fixed Reynolds number of 4000. The influence of the Reynolds number on the velocity ratio is also discussed and presented for different gap to width ratio (g/w). The flow visualisation photographs showing fluid motion inside and around the test channel are also presented and discussed.