• Journal of Power System Engineering
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• v.17 no.3
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• pp.50-56
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• 2013

The analysis of performance characteristics was carried out in the plate type evaporator with counter and parallel flow. To investigate performance of evaporator with water inlet temperature and refrigerant mass flow rate were changed. As a result, when the inlet temperature of water is $8^{\circ}C$, capacity of parallel flow evaporator higher than counter flow is 0.35%. But as the inlet temperature of water rises from $8^{\circ}C$ to $16^{\circ}C$, capacity of counter flow type evaporator higher than parallel flow type is 0.12%, 0.27%, 1.1%, 1.6%, respectively. The findings showed that counter flow type evaporator has a larger capacity than those that were parallel flow type evaporator. As the refrigerant mass flow rate rises, capacity and pressure drop increases in the counter and parallel flow type evaporator.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.305-310
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• 2007

For the understanding of the complex flow characteristics in the counter-rotating axial flow fan, it is necessary to investigate the three-dimensional unsteady flow fields in the counter-rotating axial flow fan. This information is also essential for the prediction of the aerodynamic and acoustical characteristics of the counter-rotating axial flow fan. Experimental study on the three-dimensional unsteady flow in the counter-rotating axial flow fan is carried out at the design point(operating condition). Three-dimensional unsteady flow fields in the counter rotating axial flow fan are measured at the cross-sectional planes of the upstream and downstream of each rotor using the $45^{\circ}$ inclined hot-wire. Three-dimensional unsteady flow fields in the counter-rotating axial flow such as the wake, the tip vortex and the tip leakage flow are shown the form of the velocity vectors and the velocity contours.

• Journal of Aerospace System Engineering
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• v.14 no.4
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• pp.18-24
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• 2020

The counter-flow jet from a supersonic/hypersonic vehicle causes a structural change in the shock wave generated around the aircraft, which can lead to reduced drag and heat loads. Since the idea is to mount a counter-flow jet device for drag reduction in the aircraft, it is necessary to understand the effect of such a device on the entire aircraft. In this study, the effect of drag reduction due to counter-flow jet on a conventional rocket configuration was analyzed through CFD analysis. The results showed that the drag reduction effect was the largest in the blunt region and that the counter-flow jet also affected the downstream of the aircraft. The analysis indicated that the drag reduction effect by the counter-flow jet was about 10 to 25 % when targeting the entire rocket-shaped area, while the effect was as high as 50% when targeting only blunt objects.

• Journal of Institute of Convergence Technology
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• v.5 no.1
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• pp.37-40
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• 2015

Numerical analyses on the aerodynamic characteristics of a counter rotating axial flow fan is carried out using the frequency domain panel method. Front rotor and rear rotor blades of a counter rotating axial fan are designed by using the simplified meridional flow analysis method with the radial equilibrium equation and the free vortex design condition, according to design requirements. Performance characteristics of a counter rotating axial flow fan are estimated for the variation of design parameters such as the hub to tip ratio, the taper ratio and the solidity. Pressure losses were higher at leading edge and hub region of rotor blades. Characteristic curve of the counter rotating fan was overpredicted without consideration of viscous effect.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.9
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• pp.1005-1014
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• 2004

Experiments were done for the three dimensional unsteady flow in a counter-rotating axial flow fan under peak efficiency operating condition. Flow fields in a counter rotating axial flow fan were measured at cross-sectional planes of the upstream and downstream of each rotor. Cross sectional flow patterns were investigated through the acquired data by the 45$^{\circ}$ inclined hot-wire. Flow characteristics such as tip vortex, secondary flow and tip leakage flow were confirmed through axial, radial and tangential velocity vector plot. It has been found that the radial and tangential velocity components disappeared, while the axial velocity component highly increased as soon as the tip vortex was generated. It has been observed that secondary flow and turbulence intensity which were increased by the front rotor were dissipated passing through the rear rotor. As the result the energy loss of the counter rotating axial flow fan decreased at the downstream of rear rotor. Also, it has been verified that tip vortex pattern of the rear rotor was dampened because the tip vortex generated by front rotor was mixed with that of the rear rotor.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1389-1394
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• 2004

Experiments were done for the unsteady flow in a counter rotating axial flow fan near peak efficiency and stall point. Flow fields in a counter rotating axial flow fan were measured at cross-sectional planes of the upstream and downstream of each rotor. Cross sectional passage flow patterns were investigated through the acquired data by the $45^{\circ}$ inclined hot-wire. Comparison of flow characteristics between two different operating conditions such as tip vortex, secondary flow and turbulence intensity were performed through the analyses of axial, radial and tangential velocity distributions. As a result, tip vortex and secondary flows are enforced and measured obviously at stall point.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.822-827
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• 2003

Experiments were done for the three dimensional unsteady flow in a counter rotating axial flow fan under stable operating condition. Flow fields in a counter rotating axial flow fan were measured at cross-sectional planes of the upstream and downstream of each rotor. Cross sectional flow patterns were investigated through the acquired data by the $45^{\circ}$ inclined hot-wire. Flow characteristics such as tip vortex, secondary flow and tip leakage flow were confirmed through axial, radial and tangential velocity vector plot. Swirl velocity, which was generated by the front rotor, was recovered in the form of static pressure rise by the rear rotor except for hub and tip regions.

• Journal of the Korean Electrochemical Society
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• v.11 no.1
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• pp.51-58
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• 2008

Many researches for effects of different flow configurations on performance of Proton Exchange Membrane Fuel Cell have extensively been done but the effects of flow direction at the same flow channel shape should be considered for optimal operation of fuel cell as well. In this paper a numerical computational methode for simulating entire reactive flow fields including anode and cathode flow has been developed and the effects of different flow direction at parallel flow was studied. Pressure drop along the flow channel and density distribution of reactant and products and water transport, ion conductivity across the membrane and I-V performance are compared in terms of flow directions(co-flow or counter-flow) using above numerical simulation method. The results show that the performance under counter-flow condition is superior to that under co-flow condition due to higher reactant and water transport resulting to higher ion conductivity of membrane.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.12 s.243
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• pp.1615-1620
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• 2005

We present a novel flow-rate independent cell counter using a fixed control volume between double electrical sensing zones. The previous device based on the single electrical cell sensing in a given flow-rate requires an accurate fluid volume measurement or precision flow rate control. The present cell counter, however, offers the flow-rate independent method for the cell concentration measurement with counting cells in a fixed control volume of $22.9{\pm}0.98{\mu}{\ell}$. In the experimental study, using the RBC (Red Blood Cell), we have compared the measured RBC concentrations from the fabricated devices with those from Hemacytometer. The previous and present devices show the maximum errors of $20.3\%\;and\;16.1\%$, which are in the measurement error range of Hemacytometer (about $20\%$). The present device also shows the flow-rate independent performance at the constant flow-rates ($5{\mu}{\ell}/min$ and $10{\mu}{\ell}/min$) and the varying flow-rate (4, 2, and $4{\mu}{\ell}/min$). Therefore, we demonstrate that the present cell counter is a simple and automated method for the cell concentration measurement without requiring an accurate fluid measurement and precision flow-rate control.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.201-210
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• 2002

Experiments were done for performance and flow characteristics of a counter-rotating axial flow fan. Performance curves of a counter-rotating axial flow fan were obtained and compared by varying the blade pitch angles. The fan characteristic curves were obtained following the Korean Standard Testing Methods for Turbo Fans and Blowers (KS B 6311). The fan flow characteristics were measured using a five-hole probe and a slanted hot-wire. The velocity profiles between the hub and tip of the fans were measured and analyzed at the peak efficiency point. The peak efficiency of the counter-rotating axial flow fan was improved about 15% respectively, compared with the single rotating axial fan. The single rotating axial flow fan showed relatively law efficiency due to the swirl velocities behind rotor exit which produced pressure losses. The counter-rotating axial flow fan showed that the swirl velocity generated by the front rotor was eliminated by the rear rotor and the associated dynamic pressure is recovered in the from of the static pressure rise.