• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.6
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• pp.317-323
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• 2013

A multi-perforated tube indicates the existence of multiple holes of various shapes on the surface of a long cylinder-type or rectangular tube, and a hole installed on the surface is called an orifice, as it is relatively small in size, compared with the surface area of the tube. In this study, the flow characteristics of a circular multi-perforated tube with many orifices on the surface were investigated experimentally and numerically. The volume flowrate issuing from each orifice, discharge angle, effective flow area ratio, and the flow fields around the orifices were measured and visualized, with the variation of the orifice area ratio, at the same blockage ratio. The volume flowrate distributions along the flow direction of the multi-perforated tube tends to be more uniform, as larger orifices were positioned at the inlet side of the multi-perforated tube, compared with no orifice area change along the flow direction.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.6
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• pp.416-426
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• 2008

The boiler tube failure often experienced in the superheater of a utility boiler can seriously affect the economic and safe operation of the power plant. It has been known that this failure is mainly caused by the thermal load deviation in the superheater tube system, and deeply intensified by the non-uniform distribution of steam flow rates. The nonuniform steam flow is distinctively prominent at low power load rather than at full power load. In this paper, we analyze the steam flow distribution in the superheater tube system by using one dimensional flow network model. At 30% power load, the deviation of steam flow rate is predicted to be within 0.8% of the averaged flow rate. This deviation can be reduced to 0.1% and 0.07% by assuming two cases, that is, the removal of 13th tube at each tube rows and the installation of intermediate header, respectively. The assumed two cases would be effective for the uniform steam flow distribution across 85 superheater tube rows.

• Corrosion Science and Technology
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• v.10 no.4
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• pp.125-130
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• 2011

This study was performed to improve the corrosion resistance and the stability of passive film on copper tube by potentiostatic polarization method in synthetic tap water. Formation of passive film was carried out by anodic potentiostatic polarization at various passivation potentials and passivation times in 0.1 M NaOH solution. Stability of passive film and corrosion resistance was evaluated by self-activation time, ${\tau}_0$ from passive state to active state on open-circuit state in 0.1 M NaOH solution. Addition of polyphosphate in NaOH solution prolonged the self-activation time and improved the corrosion resistance, and the addition of 5 ppm polyphosphate was most effective. It was also observed that better corrosion resistance was obtained by potentiostatic polarization at 1.0 V (vs. SCE) than at any other passivation potentials. Passivated copper tube showed perfect corrosion resistance for the immersion test in synthetic tap water showing that the anodic potentiostatic polarization treatment in 0.1 M NaOH with 5 ppm polyphosphate solution would be effective in improving the corrosion resistance and preventing the blue water problem.

• International Journal of Computer Science & Network Security
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• v.22 no.10
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• pp.423-430
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• 2022

The emergence of social media platforms has changed the culture of business marketing. Their impact has increased considerably since the emergence of social media influencers or content creators. The phenomenon of social media influencers has been adopted as one of the most effective marketing strategies among global and local organizations. Those celebrities attract business owners, who seek to use them as means to reach a large number of potential consumers. Today, the user bases of Snapchat and YouTube in Saudi Arabia are growing fast and becoming very popular, unlike other social media platforms. Consequently, the impact of these applications' influencers on the purchasing habits of individuals cannot be underestimated. This survey paper intends to investigate the impact of Snapchat and YouTube influencers on the consumption behaviour of Saudi consumers. Results suggest that Snapchat is not only more popular but also more rusted and credible. Moreover, influencers' impact on purchasing behaviour is prevalent and powerful; furthermore, its influence is more effective in persuading Saudi consumers to buy certain products, such as food, than other products, like jewelry.

• Corrosion Science and Technology
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• v.22 no.5
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• pp.322-329
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• 2023

There are a variety of heat exchangers used in automobiles, such as shell and tube heat exchangers, double tube heat exchangers, and plate heat exchangers. Most of them are water-cooled to prevent engine overheating. There have been reports of corrosion damage to these heat exchangers due to continuous wetting caused by external temperature differences, road pollutants, and snow removal. In addition, galvanic corrosion, which occurs when two dissimilar materials come into contact, has been identified as a major cause. In this study, corrosion characteristics and galvanic corrosion behavior of Al alloy (AA3003, AA4045 and AA7072) used in automobile heat exchangers were analyzed. Effective clad materials for heat exchanger tubes and fins were also evaluated. It was found that AA7072 should be applied as the cladding material for fin AA3003 and that AA4045 was suitable as a cladding material for tube AA3003 because this clad materials application was the most effective clad design to delay the occurrence of pinhole in the tube. Main factors influencing galvanic corrosion dissolution were found to be galvanic corrosion potential difference and galvanic corrosion current density.

• International Journal of Internet, Broadcasting and Communication
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• v.12 no.3
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• pp.206-212
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• 2020

The purpose of this study is to analyze the structural relationship among information attitude, brand attitude, usage satisfaction, brand image and brand loyalty of YouTube sports Contents. The survey subjects to achieve the purpose of this study were selected the 490 YouTube sports contents Viewer in the metropolitan area. Data processing was done with SPSS 23 for frequency analysis, Cronbach's α analysis. Also, AMOS 21 was used for confirmatory factor analysis and structural equation model analysis. The results of the analysis are as follows: First, it is more effective to increase the attitude toward the brand itself rather than information attitude to use satisfaction Second, both information attitude and brand attitude were found to have a positive effect on enhancing brand image. In relation to attitude and image, it was possible to achieve research accumulation for YouTube users. Third, it was found that both the use satisfaction and the brand image presented in the previous study had a positive effect on brand loyalty.

• Transactions of Materials Processing
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• v.11 no.3
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• pp.238-245
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• 2002

The spring back taking place after the coiling process of steam generator tube leads to the dimensional inaccuracy. In order to reduce the spring back, tension force was applied to the one end of the tube during forming. In this work, parametric study using FEM was performed to find the appropriate magnitude of tension force. The force that induces minimum spring back was found by simultaneously taking account if spring back amount, cross-sectional ovality, and thickness of the tube wall after deformation. In addition, stress relieving by heat treatment was also simulated as an alternative to the former method. The latter was found to be more effective under the given constraints.

• Journal of radiological science and technology
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• v.12 no.1
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• pp.25-29
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• 1989

This paper investigated on influence on the distinguishability of renal stone in the accordance with thickness of object, x-ray tube voltage and base density. In the relationship between object and renal stone shadow, object and tube voltage, the obtained results can be summarized as the following. 1. When thickness of object was thin, the distinguishability increased in base density $2.0{\sim}2.5$, but for adults was best shown in base density 1.5. 2. In the relationship between object and tube voltage, the distinguishability increased at lower tube voltages ($50{\sim}60\;kVp$), using grid. As mentioned above, it was thought that this method was very effective in describing the phenomena of renal stone in film density 1.5, tube voltages 60 kVp.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.105-111
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• 2000

A numerical study has been performed to obtain the heat transfer and pressure drop characteristics for shell-and-tube heat exchanger with various shapes of tubes. The Tubes have variation of Aspect Ratio, Pitch and Rotation. Results are presented as plots of Colburn j factor and friction factor f against Aspect Ratio, Pitch and Rotation. As Aspect Ratio increases, j factor and f factor decreases. As Pitch increases, j factor decreases. j/f have optimized Pitch for each Aspect Ratio. Accordingly, there is fitness of Aspect Ratio and Pitch fur most effective cases. The Rotation of tubes are of no meaning for both heat transfer and pressure drop.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.10a
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• pp.175-180
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• 1998

This paper describes evaluation of oxidation stability for diesel engine oils by Hot-tube oxidation tester at high temperature. Evaluation was rated by visual inspection of lacquer in capillary glass tube and TAN determination of used oil. Air, NO$_2$-air and SO$_2$-air mixed gases were used as oxidizing gas. One oil which has low oxidation stability is selected and reformulated by addition of some additives such as antioxidant, detergent and disperant to improve oxidation stability. As a results of reformulation, antioxidant and detergent was effective for improvement of high temperture oxidation stability on diesel engine oil.