• Proceedings of the KSME Conference
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• 2001.06d
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• pp.828-833
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• 2001

In this study, an analysis tool to assess the susceptibility of steam generator tubes due to the flow-induced vibration was developed. The fluid-elastic instability analysis of the U-tube bundle for CE-type steam generator was accomplished. The effective mass distribution along the U-tube was obtained to calculate the natural frequency and dynamic mode shape. Finally, stability ratios for selected tubes are obtained.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.5
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• pp.398-410
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• 2001

The flow and heat transfer characteristics for three-dimensional mixed convection flows in a radiator flat tube with U--shaped grooves are analyzed numerically. The flow and temperature fields are calculated by using the modified SIMPLE algorithm for irregular geometry. One tube specification among the various flat tube exchangers is recommended by considering the heat transfer and pressure drop. The effects of variation of coolant flow conditions and external air conditions on the flow and the thermal characteristics for the selected tube are investigated. the results show that inlet velocity of coolant flow is the very important factor in heat transfer and pressure drop, and top side is better position than the others as fin cleave to tube.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1400-1405
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• 2001

In this study, an analysis program to assess the susceptibility of steam generator tubes due to the flow-induced vibration was developed. Analysis of fluid-elastic instability and random turbulence excitation for the U-tube bundle in CE-type steam generator was accomplished. The effective mass distribution along the U-tube was obtained to calculate the natural frequency and dynamic mode shape. Finally, stability ratios and rms vibration amplitude for selected tubes are obtained.

• 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.

• Journal of the speleological society of Korea
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• v.10
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• pp.51-60
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• 1999

• Journal of Energy Engineering
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• v.21 no.4
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• pp.362-372
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• 2012

The steam generator tubes of nuclear power plants are pressure boundaries, and if tubes are leaked, the coolant with the radioactive materials was flowed out from the primary system to the secondary system and polluted the plant and the air. Recently most crack defects of tubes are stress corrosion cracks and these defects are located in expansion transition area, sludge pile-up region, and U-bend area. The most effective one of crack initiation factors in expansion transition area and U-bend area is the residual stress. According to the experiences of Korea standard nuclear plants(Optimized Power Reactor-1000), they had the stress corrosion cracks at the tube expansion transition area in early operating stage and especially lots of circumferential cracks were occurred. Therefore in this study, the distributions and conditions of residual stresses by tube expansion methods were compared and the dominant reason of a specific direction was examined.

• Journal of the Korean Solar Energy Society
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• v.25 no.1
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• pp.19-25
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• 2005

All-glass evacuated tube solar collectors consist of glass evacuated tubes and absorber tubes. Solar thermal energy from the sun is transferred to the working fluid through the glass evacuated tube and the absorber tube. Several collectors which have different absorber tubes are tested to find the effects of the absorber tube shapes and the operating conditions such as the incident heat flux and the flow rate. As the results, the efficiency of the collector which has a finned tube U tube is about $2{\sim}5%$ higher than that of the others in all cases on an average. And the collector has a finned U tube has the highest efficiency at the high flow rate and the low incident heat flux. In this condition, the outlet mean temperature is low and the heat loss becomes small. Also, it is known that the fin effect is greater than the shade effect.

• Steel and Composite Structures
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• v.32 no.1
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• pp.59-66
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• 2019

Hollow steel-reinforced concrete-filled GFRP tubular member is a new kind of composite members. Firstly set the mold in the GFRP tube (non-bearing component), then set the longitudinal reinforcements with stirrups (steel reinforcement cage) between the GFRP tube and the mold, and filled the concrete between them. Through the axial compression test of the hollow steel-reinforced concrete-filled GFRP tubular member, the working mechanism and failure modes of composite members were obtained. Based on the experiment, when the load reached the ranges of $55-70%P_u$ ($P_u-ultimate$ load), white cracks appeared on the surface of the GFRP tubes of specimens. At that time, the confinement effects of the GFRP tubes on core concrete were obvious. Keep loading, the ranges of white cracks were expanding, and the confinement effects increased proportionally. In addition, the damages of specimens, which were accompanied with great noise, were marked by fiber breaking and resin cracking on the surface of GFRP tubes, also accompanied with concrete crushing. The bearing capacity of the axially compressed components increased with the increase of reinforcement ratio, and decreased with the increase of hollow ratio. When the reinforcement ratio was increased from 0 to 4.30%, the bearing capacity was increased by about 23%. When the diameter of hollow part was decreased from 55mm to 0, the bearing capacity was increased by about 32%.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.8 s.251
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• pp.993-1000
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• 2006

Operating experience of steam generators has shown that cracks of various morphology frequently occur in the steam generator tubes. These cracked tubes can stay in service if it is proved that the tubes have sufficient safety margin to preclude the risk of burst and leak. Therefore, integrity assessment using exact limit load solutions is very important for safe operation of the steam generators. This paper provides global and local limit load solutions for surface cracks in the steam generator tubes. Such solutions are developed based on three-dimensional (3-D) finite element analyses assuming elastic-perfectly plastic material behavior. For the crack location, both axial and circumferential surface cracks, and for each case, both external and internal cracks are considered. The resulting global and local limit load solutions are given in polynomial forms, and thus can be simply used in practical integrity assessment of the steam generator tubes.

• Journal of Convergence for Information Technology
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• v.12 no.3
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• pp.141-150
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• 2022

Fluid flow and thermal characteristics of laminar nanofluid(water/Al2O3) flow in a circular U-bend tube have been studied numerically. In this study, the effect of Reynolds number and the solid volume fraction and the impact of the U-bend on the flow field, the heat transfer and pressure drop was investigated. Comparisons with previously published experimental works on horizontal curved tubes show good agreements between the results. Heat transfer coefficient increases by increasing the solid volume fraction of nanoparticles as well as Reynolds number. Also, the presence of the secondary flow in the curve plays a key role in increasing the average heat transfer coefficient. However, the pressure drop curve increases significantly in the tubes with the increase in nanoparticles volume fraction.