• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.03b
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• pp.34-34
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• 2010

This paper describes effect of the bending deformation of high voltage composite bushing with winding tension. The composite bushing can be formed, by adding silicone rubber sheds to a tube of composite materials. The FRP tube is internal insulating part of a composite bushing and is designed to ensure the mechanical characteristics. Generally the properties of FRP tube can be influenced by the winding angle, wall thickness and winding tension. As winding tension is increased glass contents was increased in the range of 70.4~76.6%. In the bending test, winding tension is increased residual deflection was decreased in the range of 14.0~12.2 mm.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.134-137
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• 2014

The noise reduction performance of a passive facility is dependent on the its length or volume. In other words, this means that the larger the size of passive facility is, the better the noise reduction performance is. The sound directivity control has been proposed as an alternative for the noise reduction without a passive facility. The purpose of this study is to investigate the correlation between the flange attached to inclined exit of the tube and sound directivity when the sound radiates from the tube to the outside. As a result, the sound radiated from flanged tube had weak sound directivity in the wide angle. Also as the flange was bigger, the sound pressure level was lower in the behind the flange.

• Transactions of Materials Processing
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• v.19 no.2
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• pp.113-119
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• 2010

Hydroforming is the technology that utilizes hydraulic pressure to form tube or sheet materials into desired shapes inside die cavities. Tube hydroforming provides a number of advantages over the conventional stamping process, including fewer secondary operations, weight reduction, assembly simplification, adaptability to forming of complex structural components and improved structural strength. In many case, hydroformed parts have to be structurally joined at some point. Therefore it is useful if the hydroformed automotive parts can be given a localized attachment flange. In this study for the numerical process design FE analysis was performed with DYNAFORM 5.5. Die parting angle and circumferential expansion ratio was optimized. With optimized condition, bulge and hydroforming experiments to form flange were performed. Forming characteristic at various pressure conditions was analyzed and optimized internal pressure condition was evaluated. The results show that flanged parts can be successfully produced by tube hydroforming process.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.6
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• pp.1001-1006
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• 2016

As consumption of energy is increasing rapidly, energy saving is emphasized in nowadays. Thermal power plant occupies a large proportion in various type of power plant. Major causes of decreased power generation efficiency on thermal power stations is deposition of fly ash. Soot Blower is a facility to remove the ash which is deposited outside of tube by steam blowing on boiler. Residual stream which caused by lance tube in soot blower cannot be discharged steam effectively in lance tube causes reducing the thickness of lance tube. On the contrary, increasing discharge ratio of steam, lance tube cannot sustain proper pressure to remove ash on tube. This study suggests increasing discharge ratio of steam with proper pressure to remove ash on tube by optimization on shape of lance tube nozzle. To optimize shape of nozzle, discharge ratio and maximum blowing pressure on nozzle is selected as object functions. Diameter of nozzle, distance between nozzles, angle of nozzle and gap between nozzle is selected as design parameters. Then the design of experiment (DOE) with an orthogonal array is performed to analyze the effect of design parameters. And grey relational analysis and analysis of mean (ANOM) is performed to optimize shape of lance tube.

• Journal of computational fluids engineering
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• v.13 no.1
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• pp.21-27
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• 2008

A numerical study for laminar flow in the entrance region of helical tubes for uniform inlet velocity conditions is carried out by means of the finite volume method to investigate the effects of Reynolds number, pitch and curvature ratio on the flow development. This results cover a curvature ratio range of 1/10$\sim$1/320, a pitch range of 0.0$\sim$3.2, and a Reynolds number range of 125$\sim$2000. It has been found that the curvature ratio does significantly effect on the angle of flow development, but the pitch and Reynolds number do not. The characteristic angle $\phi_c(=\phi/\sqrt{\delta})$, or the non-dimensional length $\overline{l}(=l\sqrt{\delta}cos(atan\lambda)/d)$ can be used to represent the flow development for uniform inlet velocity conditions. In uniform inlet velocity conditions, the growth of boundary layer delays the flow development attributed to centrifugal force, and in which conditions the amplitude of flow oscillations is smaller than that in parabolic inlet velocity conditions. If the pitch increases or if the curvature ratio or Reynolds number decreases, the minimum friction factor and the fully developed average friction factor normalized with the friction factor of a straight tube and the flow oscillations decrease.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.6
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• pp.781-788
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• 2003

In the present study, the heat and flow characteristics of a parallel-flow heat exchanger are numerically analyzed by using three-dimensional turbulent modeling. Heat transfer rate and pressure drop are evaluated using the concept of the efficiency index by varying the locations, the shapes and angles of inlet/outlet, and the protrusion height of flat tube. It is found that negative angle of the inlet improves the heat transfer rate and pressure drop. Results show that the locations of the inlet and outlet should be toward the right side and the left side to the reference model, respectively, in order to enhance the heat transfer rate and pressure drop. Increasing the height of the lower header causes pressure drop to decrease and yields the good flow characteristics. The lower protrusion height of flat tube shows the improvement of the heat transfer rate and pressure drop. The heat transfer rate is greatly affected by the parameters of outlet side such as the location and angle of the outlet. However, the pressure drop is influenced by the parameters of inlet side such as the location and angle of inlet and the height of the header.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.7
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• pp.500-511
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• 2007

The Optimal solutions of the design variables in internally finned tubes have been obtained for three-dimensional periodically fully developed turbulent flow and heat transfer. For a trapezoidal fin profile, performances of the heat exchanger are determined by considering the heat transfer rate and pressure drop, simultaneously, that are interdependent quantities. Therefore, Pareto frontier sets of a heat exchanger can be acquired by integrating CFD and a multi-objective optimization technique. The optimal values of fin widths $(d_1,\;d_2)$, fin height(h) and helix angle$(\gamma)$ are numerical1y obtained by minimizing the pressure loss and maximizing the heat transfer rate within ranges of $d_1=0.5\sim1.5mm$, $d_2=0.5\sim1.5mm$, $h=0.5\sim1.5mm$, and $\gamma=0\sim20^{\circ}$. For this, a general CFD code and a global genetic algorithm(GA) are used. The Pareto sets of the optimal solutions can be acquired after $30^{th}$ generation.

• Transactions of Materials Processing
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• v.32 no.4
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• pp.221-227
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• 2023

While tube bending is a conventional forming technique, it is still used to make curved products for load-bearing members or aesthetically pleasing parts in various manufacturing industries such as automotive, aerospace, and others. Whole or local deformation of the final product such as springback, distortion, or local buckling are of interest in metal forming or precision manufacturing. In this paper, the factors affecting the cross-sectional deformation are explored. A 5-axis stretch bending machine was used for two-dimensional bending with extruded AA6082-T4 rectangular tubes. Three different bending sequences were employed: stretch before bending, stretch after bending, simultaneous bending and stretch. Furthermore, by considering both the stretch and bending angle, cross-sectional deformation was also analyzed. It was observed that employing stretch bending techniques can effectively reduce cross-sectional deformation and contribute to overall quality enhancement. Through this study, it was revealed that these factors have an impact on the cross-sectional deformation of the tubes.

• Journal of Welding and Joining
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• v.27 no.2
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• pp.63-68
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• 2009

Microminiature heat exchanger has been applied to the gas turbine in order to increase energy efficiency. During the production of microminiature heat exchanger, however, it is very difficult to weld tube to tubesheet. In this study, therefore, welding process of resistance ring projection was used, and weld tensile tests were performed. Sound weld joint was obtained as a result of applying resistance ring projection welding to microminiature heat exchanger to tubesheet. Cold weld occurred at under 1600A. Even though tensile strength was increased with increasing current, splash occurred and tensile strength decreased at 2000A due to the excessive current. Therefore it was determine that the optimal current is 1900A. As result of tensile tests based on ASME code for tube to tubesheet weldment, rupture position was weldment due to Fs(Fractured section) of nugget, which was smaller than tube thickness (t), and it was proven as a partial strength welding because of the average joint efficiency fr = 0.90.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.12
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• pp.967-972
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• 2013

A MILD (Moderate and Intense Low oxygen Dilution) combustion, which is effective in the reduction of NOx, is considerably affected by the recirculation flow rate of hot exhaust gas to the combustion furnace. The present study used the MILD combustor, which has coaxial cylindrical tube. The outside tube of the MILD combustor corresponds to the exhaust gas passage and the inner side tube is the furnace passage. A numerical analysis was accomplished to elucidate the characteristics of exhaust gas entrainment toward the inner furnace with the changes of coanda nozzle geometrical parameters, nozzle passage gap length, nozzle passage length, nozzle angle and expansion length. The optimal configuration of coanda nozzle for the best entrainment flow rate was gap length, 0.5 mm, expansion angle, 4o and expansion length, 146 mm. The nozzle passage length was irrelevant to the exhaust gas entrainement.