• The KSFM Journal of Fluid Machinery
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• v.6 no.3 s.20
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• pp.58-63
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• 2003

The performance of turbo pump drops rapidly and it gets into break-down when the void fraction reaches above the threshold value because the impeller flow passage is choked up with air bubbles. Phenomenological understanding of break-down and pumping recovery mechanisms under air-water two-phase flow conditions are therefore important for pump designers and essential assignment for researchers. In this paper, we investigated the characteristics of break-down and pumping recovery due to entrained air occurring inside a screw-type centrifugal pump which has a wide flow passage mainly through the findings of suction and discharge pressures, rotational speed, flow rate measurements and visualization.

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1604-1615
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• 2023

In an open-pool type research reactor with a downward forced flow in the core, pipes can be under sub-atmospheric pressure because of the large pressure drop at the reactor core in the atmospheric pool. Sub-atmospheric pressure can result in air inflow into the pipe from the pressure difference between the atmosphere and the inside of the pipe, which in a postulated pipe break scenario can lead to the breakdown of the cooling pump. In this study, a plant-scale experiment was conducted to study air inflow in large piping systems by considering the actual operational conditions of an advanced research reactor. The air inflow rate was measured, and the entrained air was visualized to investigate the behavior of air inflow and flow regime depending on the pipe break size. In addition, the developed drift-flux model for a large vertical pipe with a diameter of 600 mm was compared with other correlations. The flow regime transition in a large vertical pipe under downward flow was also studied using the newly developed drift-flux model. Consequently, the characteristics of two-phase flow in a large vertical pipe were found to differ from those in small vertical pipes where liquid recirculation was not dominant.

• Journal of the Korea Society of Computer and Information
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• v.17 no.2
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• pp.87-94
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• 2012

Mechanical break system used in train, that mixed air break & electronic break system. this system suggest lots of ways for modify efficiency and solution of environmental problems due to recently intend to green growth. The mechanical break system has environmental & economical problem. Environmental sides(problem) are dust and noise etc and economical sides(problem) are replaced the spare parts that are breaking shoe and lining ect. For compensate those kind of weak points, we needs a wide territories of electronic break which is from high speed range to stop. This research is estimated the load torque due to an incline and stop the train method also check the characteristic of stop the train to estimate a torque follow the sharp drop.

• Fibers and Polymers
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• v.5 no.3
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• pp.204-208
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• 2004

The present paper reports the detailed study on the splicing behavior of viscose staple fiber yarns made from ring, rotor, friction and air-jet spinning technologies. The linear density of all the yearns was kept constant at 29.5 tex. The splicing parameters like splicing pressure and duration of the splicing were taken as variables. Three levels of splicing pressure at constant splicing duration and three levels of splicing durations at constant splicing pressure were considered. Splices were introduced at all these levels for the four different technologies. These splices were tested for their tensile properties and the properties of splices were evaluated in terms of retained splice strength (RSS) and splice break ratio (SBR). The splice photographs were taken and splices were analyzed for their structure and for diameter profile along the length of the splice.

• Journal of Electrical Engineering and Technology
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• v.13 no.2
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• pp.918-927
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• 2018

Based on the actual operating environment of transformer, the aging tests of nitrile butadiene rubber (NBR) were conducted systematically under four conditions: in air, in transform oil, under compression in air and under compression in transform oil to studythe effect of high temperature, transform oil and compression stress simultaneously on the thermal aging behaviors of nitrile butadiene rubber and predict the lifetime. The effects of liquid media and compression stress simultaneously on the thermal aging behaviors of nitrile butadiene rubber were studied by using characterization methods such as IR spectrosc-opy, thermogravimetric measurements, Differential Scanning Calorimetry (DSC) measurements and mechanical property measurements. The changes in physical properties during the aging process were analyzed and compared. Different aging conditions yielded materials with different properties. Aging at $70^{\circ}C$ under compression stress in oil, the change in elongation at break was lower than that aging in oil, but larger than that aging under compression in air. The compression set or elongation at break as evaluation indexes, 50% as critical value, the lifetime of NBR at $25^{\circ}C$ was predicted and compared. When aging under compression in oil, the prediction lifetime was lower than in air and under compression in air, and in oil. It was clear that when predicting the service lifetime of NBR in oil sealing application, compression and media liquid should be involved simultaneously. Under compression in oil, compression set as the evaluation index, the prediction lifetime of NBR was shorter than that of elongation at break as the evaluation index. For the life prediction of NBR, we should take into account of the performance trends of NBR under actual operating conditions to select the appropriate evaluation index.

• Proceedings of the KIEE Conference
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• summer
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• pp.551-553
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• 2004

SF_6 gas has been increasingly used as the insulating and arc-suppressing medium in switchgears which are used as the protection devices of power system. Nowadays, with these trends, SF_6 load break switches have rapidly substituted for the air or oil-type load break switches, in order to get higher reliability. And, the national standard was made for reliability assessment of SF_6 gas load break switch and testing facilities was also set in KERI(Korea Electrotechnology Research Institute ). This paper introduces the synopsis for the reliability assessment requirements specified in the standard and the assessment results.

• JOURNAL OF ELECTRICAL WORLD
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• no.10 s.106
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• pp.22-27
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• 1985

• Journal of ILASS-Korea
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• v.1 no.1
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• pp.63-75
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• 1996

The purpose of this study is to investigate the break-up characteristics by taking advantage of a two-phase coaxial nozzle. Air and water are utilized as working fluids and the mass ratio air/water has been controlled to characterize the atomization, diffusion and development of mixing process. By way of a photographic technique, conventional developing structures and diffusion angles have been analyzed systematically with variations of mass ratios. The turbulent flow components of the atomized particles were measured by a two channel LDV system and the data were treated by an on-lined measurement equipment. According to the photographic results the spreading angles decreased because the axial inertia moment was relatively higher than the lateral one with respect to the increase of mass ratio. It is found the jet flow diffuses linearly in a certain limit region while the atomizing characteristics, in terms of the distributions of particle diameters did not show particular differences. It may be expected that these fundamental results can be used as reference data in studying the atomization, breakup and diffusions.

• Proceedings of the KIEE Conference
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• summer
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• pp.560-562
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• 2004

$SF_6$ gas has been increasingly used as the insulating and arc-suppressing medium in switchgears which are used as the protection devices of power system. Nowadays, most of power companies adopted the $SF_6$ gas-type load break switch for increasing the reliability of distribution network by its superior durability against external environmental condition, in substitution for air-type and oil-type switches. But, it is important to establish the general estimation process for the testing and estimation for long-term reliability Accordingly, the national standard(RS C0031) was made for the reliability assessment of $SF_6$ gas load break switch and the testing facilities were also set in KERI(Korea Electrotechlology Research Institute). This paper presents the requirements of RS C0031 for reliability assessment of $SF_6$ gas load break switch and synopsis of the accelerated life testing facilities for $SF_6$ gas load break switch.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.8
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• pp.1203-1210
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• 2004

It was reported recently that the pump head degradation near the best efficiency point from single-phase flow to the break-down due to air entrainment became less in a screw-type centrifugal pump than in a general centrifugal pump. In this paper, I carried out internal pressure measurements and visualizations, and investigated the various physical phenomena occurring inside a screw-type centrifugal pump operated in air-water two-phase flow. The results could give some characteristics about the degradation of pump performance on air-water two-phase flow.