• Proceedings of the KSME Conference
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• 2000.04b
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• pp.795-800
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• 2000

A CCFL(Counter Current Flow Limit) test have been performed in narrow annular gaps with large diameter, because it has been confirmed that the CCFL phenomena affected the critical power in hemispherical narrow gap geometries from the SONATA(Simulation Of Naturally Arrested Thermal Attack)-IV (In-Vessel)/VISU(Visualization)-II experiments. The objectives of the CCFL experiments are to investigate the small gap sizes(1, 2mm) effect on CCFL under the large diameter condition and to confirm the findings of the VISU-II study that global dryout in hemispherical narrow gaps was induced by the CCFL. The test section was made of acrylic resin to allow visual observation on the two-phase flow behaviors inside annular gaps. It was observed from visualization that a part of water supplied was accumulated in the upper plenum and a significant increase in the differential pressure across the gap was occurred, which was the definition of the CCFL occurrence in this experimental study. From the experimental results in annular gap with large diameter it can be known that an increase in the differential pressure was not big at small air flow-rates. When the CCFL was occurred, the differential pressure across gaps was increased significantly and a water accumulated in the upper plenum. The occurrence of CCFL was correlated using the Wallis parameter.

• Nuclear Engineering and Technology
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• v.34 no.4
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• pp.396-405
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• 2002

An experimental study on counter-current flow limitation phenomena in narrow annular passages was carried out The gap sizes tested were 1, 2 and 3 mm. This is very small compared with the outer diameter of the annular passage, 500 mm. It was visually observed that a CCFL might occur in some part of the periphery while the other part is remained in a counter current flow pattern. That is, non-uniform behaviour of fluids due 4o a 2-dimensional effect appear in a large diameter facility. Because of this non-uniformity, a CCFL is defined in the present work as the situation where net water accumulation is sustained. That is, some amount of water should not be allowed to penetrate the gap and accumulate over the gap at CCFL criterion. The measured data are presented in the form of Wallis＇type correlation with characteristic length of gap size. It was found that the present correlation is in good agreement with other empirical correlation based on measurements whose test section diameter is close and the gap size is much larger than that of the present test section.

• Journal of electromagnetic engineering and science
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• v.5 no.3
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• pp.146-151
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• 2005

Electromagnetic penetration into an annular aperture in a thick conducting plane is investigated with the integral transform and eigen-function expansion method. The solution is analytic and is represented in rapidly-convergent series which is amenable to numerical analysis. Numerical computations shows that apertures with narrow annular gap have sharp transmit power peaks in frequency response.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.136-141
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• 2000

A study of counter-current two-phase flow in narrow rectangular channels has been performed. Two-phase flow regimes were experimentally studied in 760 mm long and 100 mm wide test sections with 2.0 and 3.0mm gaps. The resulting data have been compared to previous transition models. For the transition from bubbly to slug flow the superficial velocity of gas increased as the gap width increased. The comparison of experimental data to the transition model developed by Taitel and Barnea showed relatively good agreement for the bubbly-to-slug transition in the case of 2mm gap width. For the criteria of Mishima and Ishii to be applicable to the slug-to-churn transition the distribution parameter should be well defined for narrow channels. Even though the gap width of narrow channels increased the superficial gas velocity did not change for the transition form chum to annular flow regime. For the chum-to-annular transition the model of Taitel and Barnea showed discrepancies with experimental data, especially in the channel with larger gap.

• Progress in Superconductivity and Cryogenics
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• v.10 no.4
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• pp.1-5
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• 2008

Flow and heat transfer characteristics of liquid nitrogen in narrow annular channels are very important for many practical applications. In the present study, the experimental investigation of flow boiling of liquid nitrogen in narrow annular channels with gap size of 0.2 and 0.5 mm is carried out. The pressure drop and heat transfer coefficients are experimentally measured. The comparison of the theoretical models for the pressure drop and the correlations of the flow boiling to the experimental results are carried out.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.3
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• pp.329-338
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• 2001

In this paper, we designed microstrip patch antenna to enhance the weak point of general microstrip patch antenna that has narrow bandwidth and analyzed that. To reduce reactance in probe feed antenna, capacitive gap added to the patch. Using single patch and auxiliary wire, makes dual frequency resonant. So bandwidth is improved and gain also becomes higher. To verify with experiment, PCS band antenna is designed, fabricated. For PCS band antenna, bandwidth is 180 MHz in VSWR<1.5 and gain is 8.6 dBi.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.1
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• pp.212-222
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• 1994

In the annular Modified Chemical Vapor Deposition process using two concentric tubes, the inner tube is heated to maintain high temperature gradients to have high thermophoretic force which can increase particle deposition efficiency. However, higher axial velocity in a narrow gap between inner and outer tubes can result in a longer tapered entry length. In the present paper, a new concept using an annular jet from the inner tube is presented and shown to significantly reduce the tapered entry length with maintaining high efficiency. Effects of a jet injection on heat transfer, fluid flow and particle deposition have been studied. Of particular interests are the effects of jet velocity, jet location and temperature on the deposition efficiency and tapered length . Torch heating effects from both the previous and present passes are included and the effect of surface radiation between inner and outer tubes is also considered.

• Journal of Mechanical Science and Technology
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• v.15 no.7
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• pp.941-950
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• 2001

A study of counter-current two-phase flow in narrow rectangular channels has been performed. Two-phase flow regimes were experimentally investigated in a 760mm long and 100mm wide test section with 2.0 and 5.0mm gap widths. The resulting flow regime maps were compared with the existing transition criteria. The experimental data and the transition criteria of the models showed relatively good agreement. However, the discrepancies between the experimental data and the model predictions of the flow regime transition become pronounced as the gap width increased. As the gap width increased the transition gas superficial velocities increased. The critical void fraction for the bubbly-to-slug transition was observed to be about 0.25. The two-phase distribution parameter for the slug flow was larger for the narrower channel. The uncertainties in the distribution parameter could lead to a disagreement in slug-to-churn transition between the experimental findings and the transition criteria. For the transition from churn to annular flow the effect of liquid superficial velocity was found to be insignificant.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.695-701
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• 2001

While a rotating inner cylinder executes a periodic translational motion in concentric annulus, the vibration of the rotating inner cylinder is induced by fluid-dynamic forces acting on the cylinder. In the previous study related to journal bearing, the unsteady viscous flow in the annulus and the fluid-dynamic forces were evaluated based on a numerical approach. Considering the dynamic-characteristics of unsteady viscous flow, an approximate analytical method has been developed for estimating added mass, viscous damping and fluid-stiffness coefficients. For the study of flow-induced vibrations and related instabilities, it is of interest to separate the coefficients from the fluid-dynamic forces. The added-mass and viscous damping coefficients for very narrow annular configurations, as journal bearing. can be approximated by considering the gap ratio to the radius of inner cylinder, while the fluid-stiffness coefficient is related to the Reynolds number, the oscillatory Reynolds number and the gap ratio.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.12
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• pp.1061-1069
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• 2010

In this study, a simplified axisymmetric model is proposed for the problem of compressible internal flow past a microgap. Using numerical and experimental methods, the phenomena of choked flows are observed; these flows are induced by the acceleration of subsonic flows past the narrow cross-section of an annular shape made by a microgap. The relation between mass flow rate and differential pressure is obtained, and by comparing the result with experimental results, the reliability of the numerical results is discussed. The generation of a supersonic jet flow and its diffraction are visualized by performing the numerical analysis of axisymmetric compressible Navier-Stokes equations. This investigation greatly extends the physical understanding of the axisymmetric compressible flow, which has a wide range of engineering applications, e.g., in the case of valves in automotive power systems.