• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.285-288
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• 2003

The bending phenomenon during extruding one product using four billets can be obtain by the difference of hole diameters in the multi-hole container. The difference of hole diameter caused the difference of billet amount inserted in the die cavity. As results, it can bend during extruding products by the different amount of two billets and by the cohesion of billets in the porthole dies cavity. And the bending curvature can be controlled by the size of holes and billets. The experiments using aluminium material had been done for the rectangular and square curved tube product. The results of the experiment show that the curved aluminum tube product can be bended by the extru-bending process without the defects such as the distortion of section and the thickness change of the wall of tube and the folding and wrinkling. The curvature of product is affected by shape of cross section and the difference of billet diameters. It is known that the welding and extruding and bending can be done simultaneously in the die cavity when a rectangular hollow curved tube would be extruded by porthole dies using four different size billets made of aluminum material.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.7
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• pp.1006-1013
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• 2004

Operating experience of steam generators shows that the tubes are degraded by stress corrosion cracking, fretting wear and so on. These defected tubes could stay in service if it is proved that the tubes have sufficient structural margin to preclude the risk of tube bursting. This paper provides detailed plastic limit pressure solutions for through-wall cracks in the steam generator tubes. These are developed based on three dimensional(3D) finite element analyses assuming elastic-perfectly plastic material behavior. Both axial and circumferential through-wall cracks in free span and in u-bend regions are considered. The resulting limit pressure solutions are given in a polynomial form, and thus can be simply used in practical integrity assessment of the steam generator tubes.

• Journal of the Korean Society of Visualization
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• v.1 no.2
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• pp.38-46
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• 2003

An experimental investigation was performed to study the turbulent characteristics of swirling flow a 90$^{\circ}C$ circular tube for Re = 10,000, 15,000 and 20,000. 2D-PIV(Particle Image Velocimetry)technique was employed to measure the fluctuation velocity field. The results include spatial distributions of mean velocity vectors, turbulence intensity and turbulence kinetic energy. The axial and radial turbulence intensities, and kinetic energy profiles show double-peak structures in the inlet region of the 90 degree bend and the profiles are disappeared along the test tube with decaying the swirl intensity.

• International Journal of Air-Conditioning and Refrigeration
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• v.16 no.1
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• pp.22-29
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• 2008

A sequence of visually experimental observations was conducted to investigate the flow boiling and two-phase flow in a coiled tube. Different boiling modes and bubble dynamical evolutions were identified for better recognizing the phenomena and understanding the two-phase flow evolution and heat transfer mechanisms. The dissolved gases and remained vapor would serve as foreign nucleation sites, and together with the effect of buoyancy, centrifugal force and liquid flow, these also induce very different flow boiling nucleation, boiling modes, bubble dynamical behavior, and further the boiling heat transfer performance. Bubbly flow, plug flow, slug flow, stratified/wavy flow and annular flow were observed during the boiling process in the coiled tube. Particularly the effects of flow reconstructing and thermal non-equilibrium release in the bends were noted and discussed with the physical understanding. Coupled with the effects of the buoyancy, centrifugal force and inertia or momentum ratio of the two fluids, the flow reconstructing and thermal non-equilibrium release effects have critical importance for flow pattern in the bends and flow evolution in next straight sections.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.3
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• pp.313-318
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• 2012

In CANDU, feeder pipes supply heavy water to pressure tube and steam generator. Under service conditions, Flow-Accelerated Corrosion (FAC) produces local wall-thinning in the feeder pipes. The wall-thinning in these pipes affects the integrity of the piping system, as verified in previous research. This paper provides limit loads for wallthinned feeder pipes with $45^{\circ}$ and $60^{\circ}$ bend angles, and proposes an equation that predicts the limit loads for wallthinned feeder pipes with arbitrary bend angles. On the basis of finite element limit analyses, limit loads are obtained for wall-thinned feeder pipes under in-plane bending and internal pressure. There are two cases of in-plane bending: the in-plane closing direction and the in-plane opening direction. The material is considered the effect of the large deformation, so an elastic-perfectly-plastic material is assumed in the calculations.

• Progress in Superconductivity and Cryogenics
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• v.25 no.2
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• pp.19-24
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• 2023

Recently, interest in renewable energy such as solar and wind power has increased as an alternative to fossil fuels. Renewable energy sources such as large wind farms require long-distance power transmission because they are located inland or offshore, far from the city where power is required. High-Temperature Superconducting (HTS) power cables have more than 5 times the transmission capacity and less than one-tenth the transmission loss compared to the existing cables of the same size, enabling large-capacity transmission at low voltage. For commercialization of HTS power cables, unmanned operation and long-distance cooling technology of several kilometers is essential, and pressure drop characteristic is important. The cryostat's spiral corrugation tube is easier to bend, but unlike the round tube, the pressure drop cannot be calculated using the Moody chart. In addition, it is more difficult to predict the pressure drop characteristics due to the irregular surface roughness of the binder wound around the cable core. In this paper, a CFD model of a spiral corrugation tube with a core was designed by referring to the water experiments from previous studies. In the four cases geometry, when the surface roughness of the core was 10mm, most errors were 15% and the maximum errors were 23%. These results will be used as a reference for the design of long-distance HTS power cables.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.10a
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• pp.383-388
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• 1995

Two-phase transient phenomena in the noncondensable gas-filled closed loop was investigated numerically using the RELAP5/MOD3 version 3.1 computer code. The condensation heat transfer correlation for noncondensable gases was studied in detail. Two modes of the reflux condensation which can be characterized by countercurrent flow of steam and its condensed water and the oscillatory between reflux condensation and natural circulation were predicted well. However, the natural circulation mode which the condensed water carried over the U-bend concurrently with steam was failed to predict.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1993.10a
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• pp.307-315
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• 1993

A direct draft measurement system was developed based on the swingle tree- the rear component of the single-animal harnessing (or yoking) system . The prototype was made from a tube, on which four strain gages were attached. The pull of the draft animal through the flexible pull chains or ropes causes the beam to bend, The bending strain is sensed by the strain gages and the bridge converts this to a voltage signal. Counterweights keep the tube correctly oriented if the angle of pull changes , while end bearing follow the variations in the angle of pull. Hence, the voltage output is proportional to the draft. the device has highly linear response, acceptable sensitivity negligible error and hysteresis. It is suitable for electronic data acquisition, non-intrusive , easy to attach and detach and is reasonably priced.

• Nuclear Engineering and Technology
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• v.30 no.4
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• pp.377-385
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• 1998

Many nuclear power plants have experienced unscheduled shutdown due to the leakage of steam generator tubes. The leakages are normally due to the crack, possibly stress corrosion cracking (SCC) near the tube expansion at the top of tubesheet or at the tangential point of the row-1 U-bend region. The conventional eddy current technique, which makes use of a differential bobbin coil, has been found to be inadequate for the early detection of SCC. During the in-service inspection, therefore, it is a general practice that the rotating pancake coil (RPC) is used for detecting the cracks. Even in using RPC, however, it is difficult to determine the depth of the cracks quantitatively. This paper attempts to determine the detectability and sizing ability of RPC technique for axial or circumferential cracks at the tube expansion region. The simulated cracks with various dimensions were fabricated by electro-discharge machining (EDM) method. Experimental results are discussed with theoretical calculations.

• Transactions of Materials Processing
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• v.13 no.8
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• pp.663-670
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• 2004

The bending phenomenon has been known to be occurred by the difference of velocity at the die exit. The difference of velocity at the die exit section can be obtained by the different velocity of billets through the multi-hole container. The difference of velocity at the die exit can be controlled by the two variables, the one of them is the different velocity of extrusion punch through the multi-hole container, the other is the difference of hole diameter of muliti-hole container. In this paper the difference of hole diameter is applied. So it can bend during extruding products because of the different amount of two billets when billets would be bonded in the porthole dies cavity. And the bending curvature can be controlled by the size of holes. The experiments with aluminum material for the curved tube product had been done for circular or rectangular curved tube section. The results of the experiments show that the curved tube product can be formed by the extru-bending process without the defects such as distortion of section and thickness change of wall of tube and folding and wrinkling. The curvature of product can be controlled by shape of cross section and the difference of billet diameters. And it is known that the bonding and extruding and bending process can be done simultaneously in the die cavity by the experiments that rectangular hollow curved tubes could be extruded by porthole dies with four different size billets made of aluminum material. And it shows that bending phenomenon can happen during extruding with for different billets from the analysis by DEFORM-3D.