• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.3
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• pp.174-178
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• 2015

This paper describes a signal processing technique for identifying signals from defects by using an electromagnetic-ultrasonic guided waves method based on a magnetostrictive sensor that generates a torsional mode (T(0, 1)). Because this technique is based on the digital filtering, the filtered signals provide information on the relationship between the cutoff frequency of band-pass filter and the characteristic of defect signals in heat exchange tubes. To verify the performance of the technique, artificial defects with various thickness reduction ration and shape were machined in titanium tubes, and digital filtering results are reported. The results show that digital filtering provides information to the identify shape of defects and the contact condition between the tube and support ring. Therefore, the proposed technique has good potential as a tool for evaluating the integrity of heat exchange tubes.

• Journal of Power System Engineering
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• v.5 no.4
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• pp.18-23
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• 2001

This paper is to present the results of a comprehensive study on heat transfer in annuli with spirally corrugated inner tubes in the turbulent regime. Tube surface-temperature measurements were used to explain the enhancement phenomena in the annuli with several different corrugated tubes. Nusselt numbers were between 1.1 and 2 times the smooth annulus values. These enhancement values can be used to determine the appropriate range of applicability for spirally corrugated annuli.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.115-118
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• 2004

In this study, amplitudes of turbulence excitation are obtained for selected tubes inside the KSNP SG and their normal work-rates are investigated to estimate the magnitude of fretting-wear. From the results of numerical calculation, row 40&41 tubes show the maximum work-rates. Up to this row number, the work-rates inside the row 41 have much larger values than those of outside tubes. This phenomenon reveals the particular central one which has larger normal work-rate than that of outside zone. It turns out that both of the higher local mode at the U-bend region and the larger value of effective mass in the central region Increase the normal work-rate enormously.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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• pp.35-39
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• 2000

Three-dimensional rigid plastic FEM is adopted to analyze the extruding-bulging process of tee tubes. Equivalent strain-rate stress distributions and the deformation characteristic in extruding-bulging process of tee tubes are revealed which provide scientific and reliable basis for correctly designing technologcial scheme and rationally selecting parameters. meanwhile some approaches for three-dimensional rigid plastic FEM are also discussed in this paper

• Transactions of Materials Processing
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• v.15 no.8 s.89
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• pp.568-573
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• 2006

In order to numerically evaluate automotive hydro-formed DP-steel tubes on crash performance considering welding heat effects, the finite element simulations of crash behavior were performed for hydro-formed tubes with and without heat treatment effects. This work involves the mechanical characterization of the base material and the HAG-welded zone as well as finite element simulations of the crash test of hydro-formed tubes with welded brackets and hydro-forming of tubes. The welding heat effects on the crash performance are evaluated in efforts to improve the process optimization procedure of the engine cradle in the design stage. In particular, FEM simulations on indentations have been performed and experimentally verified for material properties of weld zone and heat affected zone.

• Tribology and Lubricants
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• v.25 no.4
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• pp.250-255
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• 2009

Oxidation characteristics of Zirlo and Zircaloy-4 tubes, which are widely used as nuclear power fuel cladding, are studied in steam environment up to $1200^{\circ}C$. Oxidation resistances are compared in terms of the mass increase due to the absorption of oxygen. The evolution of microscopic structure accompanied with the oxidation process is investigated. Also, the influence of oxidation on the fretting wear characteristics of the tubes is studied. Piezo-electrically actuated rig is employed to fret the tubes with cross-contacting arrangement. Wear scar is observed and measured, by using microscopes and a 3D-profiler. The results of fretting wear are quantified in terms of scar size, wear volume and wear coefficient, and compared for the three different tube materials of oxidated Zirlo, virgin Zirlo and Zircaloy-4.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.4
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• pp.524-530
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• 2003

This paper presents a new model on deformation characteristics of cylindrical tubes under pure bending. The model is based on the upper bound method that minimizes total strain energy of a system. It does not assume inextensibility condition. Geometric relations and displacement fields are derived by analysis of deformation behaviors of elastic tubes. Simulations are calculated using numerical optimization and integration techniques. The results give information about cross-sectional deformation of cylindrical tubes. Simulation results are compared with available data in literatures, which show that this method predicts deformation characteristics of tube bending process.

• Korean Journal of Materials Research
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• v.16 no.2
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• pp.111-115
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• 2006

High-finned tubes have good thermal conductivity and have better cooling efficiency than plain tubes or low-fined tubes due to bigger air contact area. During high-fined tubes are manufactured by roll forming, the main technique is illustrated to optimizing primary material(copper pipe), optimized die matrix designing technique for roll forming, control manufacturing speed to develop productivity etc. In this study, a roll forming system was developed in oder to produce high-finned tube. Also a multi-step roll forming die was designed & built to produce high-finned tube that has over 10 mm fin height. And then, roll forming test using copper pipe was performed to produce high-finned tube. Roll forming process for producing highfinned tube was optimized by analyzing and adjusting misrostructure, hardness, and surface roughness of roll formed high-fined tube.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07a
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• pp.732-736
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• 2005

Discussion of this study is that a horizontal deflection system satisfactory of operating at horizontal scan rates from 30KHz to 50KHz has been developed. It will be used in the large-area, color, high-resolution and multi-sync rear-projection CRT display device. Its characters, including the description, analysis and deflection circuit loss, are presented.

• Corrosion Science and Technology
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• v.11 no.3
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• pp.82-88
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• 2012

The thickness and chemical composition of oxides on heat recovery steam generator tubes of combined cycle power plant were examined in order to evaluate the corrosion of the tubes. Tubes were removed from the plant after actual operations for 21,482, 42,552 and 56,123 hours respectively. Thickness and growth rate of the oxide scale on reheater inner tube (SA213-T22) were very high compared to those other tubes. The oxide scale was about $250{\mu}m$ thick and uniform. The components of the scale were iron oxides. The oxide scale was mixed oxides consisting of magnetite$(Fe_3O_4)$ and hematite$(Fe_2O_3)$. The oxide on inner tube was removed using many kinds of chemicals and it was found that chelating agents were dissolved faster than other chemicals.