• Journal of computational fluids engineering
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• v.17 no.2
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• pp.93-99
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• 2012

The present study focuses on the case of developing flow with in a channel containing a long array of sinusoidal waves (2a/${\lambda}$=0.1, ${\lambda}$=h, ${\lambda}$ is the wavelength, 2a is the wave height, h is the mean channel depth) at the bottom wall. The Reynolds number defined with channel height, h and the mean velocity, U, is Re=6,700. The channel is sufficiently long such that transition is completed and the flow is fully developed over the downstream half of the channel. For the case of an incoming steady flow with no resolved turbulence, the instantaneous flow fields in the transition region are characterized by the formation of arrays of highly-organized large-scale hairpin vortices whose dimensions scale with that of the roughness elements. The paper explains the mechanism for the formation of these arrays of hairpin vortices and shows these eddies play the primary role in the formation of the large-scale streaks of high and low velocity over the wavy wall region. The presence of resolved turbulence in the incoming flow, reduces the streamwise distance needed for the streaks to develop over the wavy region, but does not affect qualitatively the transition process. In the fully-developed region, isolated and trains of large-scale hairpins play an important role in the dynamics of the streaks over the wavy wall.

• Biomolecules & Therapeutics
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• v.13 no.1
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• pp.35-40
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• 2005

This study was performed to investigate the regulatory mechanism of cerebral blood flow of adenosine A$_{2B}$ receptor agonist in the rats, and to define whether its mechanism is mediated by adenylate cyclase, guanylate cyclase and potassium channel. In pentobarbital-anesthetized, pancuronium-paralyzed and artificially ventilated male Sprague-Dawley rats, all drugs were applied topically to the cerebral cortex. Blood flow from cerebral cortex was measured using laser-Doppler flowmetry. Topical application of an adenosine A$_{2B}$ receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA; 4 umol/I) increased cerebral blood flow. This effect of NECA (4 umol/I) was not blocked by pretreatment with adenylate cyclase inhibitor, MDL-12,330 (20 umol/I). But effect of NECA (4 umol/I) was blocked by pretreatment with guanylate cyclase inhibitor, LY-83,583 (10 umol/I) and pretreatment with ATP-sensitive potassium channel inhibitor, glipizide (5 umol/I). These results suggest that adenosine A$_{2B}$ receptor increases cerebral blood flow. It seems that this action of adenosine A$_{2B}$ receptor is mediated via the activation of guanylate cyclase and ATP-sensitive potassium channel in the cerebral cortex of the rats.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.5
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• pp.571-579
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• 2007

This study was conducted to qualify the equality of the flow distribution from open channel between rapid mixing basin and flocculation basins in a domestic full-scale water treatment plant, and suggest a remedy for improving the equality. In order to evaluate the feasibility of the suggested remedy, computational fluid dynamics (CFD) technique are used, and for verifying the CFD simulation results wet tests were carried out for the pilot scale channel based on geometric similarity. From the results of CFD simulation and wet tests, it was investigated that the modification of hydraulic structure in the distribution channel, which is to install the longitudinal orifice baffle in flow direction, could improve the equality of the flow distribution. Also, in the case that Froude number is relatively small (Froude number <<0.03), the open ratio of orifices on the installed baffle hardly affects the equality of flow distribution.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.5
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• pp.550-556
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• 2022

In this study, the flow uniformity was analyzed by performing numerical analysis on the 1 kWe internal manifold type solid oxide fuel cell stack according to the channel height of the separator. Also, it was examined by varying the fuel utilization rate and oxygen utilization rate. From the calculation results, we found that as the channel height of the separator decreased, the pressure drop increased exponentially. In addition, it was found that as the channel height of the separator decreased, the gas flow resistance inside the unit cell increased, and the flow resistance increased the pressure drop, thereby improving the flow uniformity inside the stack. Finally, the calculation results showed that as the fuel and oxygen utilization increased, the flow uniformity also improved.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.70-70
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• 2003

• Journal of the Society of Naval Architects of Korea
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• v.40 no.4
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• pp.22-29
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• 2003

New high-speed depressurized circulating water channel was designed by using the CFD code. Flow in the channel has free surface and pressure in the test section can be depressed. In this study, Flow separation and bubble occurrence were considered in designing the contraction nozzle shape for better flow uniformity Tn the test section. To supplement velocity defect due to the free surface, nozzle injection system more effective in high-speed flow was installed instead of drum system. Necessary power and injection techniques were proposed. And guide vane arrangement was analyzed to reduce the flow resistance and keep quiet free surface from ´surging´. Wave absorber was devised to reduce the wave resistance and to prevent the entrainment of air to the diffuser.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.1
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• pp.17-24
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• 2003

A mathematical model of the hydrodynamic and heat transfer performances of two-phase flow (gas-liquid) in thin film region of micro channel is proposed. For the formulation of modeling, the flow of the vapor phase and the shear stress at the liquid-vapor interface are considered. In this work, disjoining pressure and capillary force which drive the liquid flow at the liquid-vapor interface in thin film region are adopted also. Using the model, the effects of the variations of channel height and heat flux on the flow and heat transfer characteristics are investigated. Results show that the influence of variation of vapor pressure on the liquid film flow is not negligible. The heat flux in thin-film region is the most important operation factor of micro cooler system.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1098-1103
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• 2004

In this study, the effect of channel flow in the concave surface on local heat transfer characteristics of array jets was investigated experimentally. A TLC method is employed to determine local heat transfer coefficients on the target plate and also flow visualization has been conducted to investigate the behavior of a row of impinging jets and array of impinging jets. Two different array patterns of impinging array jets devices are tested for Reynolds number(Re=10,000). In a row of impinging jets, secondary vortex is strongly maintained by main vortex at nozzle-to-plate distance of H/d=2. Therefore, the Nusselt number slowly decreased at the mid-way region between adjacent jets. In array jets, the local maximum Nusselt number region move further in the downstream direction due to the increase of channel flow velocity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.2
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• pp.154-159
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• 2004

A new microflow rate controller for medical injection was developed and evaluated. The flow rate was controlled by changing the friction depth as well as the friction length of the micro-channel. A precise micro-fabrication of the micro-channel was requested for an accurate flow control. The friction depth was inversely proportional to the friction length, which gives a linear flow control to the channel length. The channel groove was fabricated with a plastic material. A rubber containing silicone oil was covered over the groove, which satisfies both lubrication and leakage prevention. The flow controller was validated by performing the numerical simulation and experiment. A good agreement was shown between computation and experiment.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.4
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• pp.324-331
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• 2004

Particle Image Velocimetry (PIV) measurements have been carried out to investigate the pulsatile flow characteristics in a triangular grooved channel. The results showed that a vortex was generated at the tip of the groove and flowed into the groove rotating inside during the acceleration phase of the main stream promoting the mixing of the fluid. Then, at the deceleration phase of the main stream, the vortex entrained fluid from the relatively slow moving main stream to grow bigger than the groove size. Finally the vortex was ejected to the main stream carrying the fluid away from the groove, resulting in the enhancement of mixing between the stagnant fluid in the groove and the main stream in the channel. It was found that the fluid mixing enhancement is maximized when the pulsatile period is the same as the time duration which the vortex takes to grow larger enough to fill the groove and to be ejected to the main stream.