• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1293-1300
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• 2011

The configurations of the evaporator and condenser of a water chiller can be determined from the trade-off between the heat transfer area, which is related to the capital cost and the pressure drop, which is associated with the operational cost. In this study, the design of the water chiller focused on minimizing the water pressure drop of both condenser and evaporator for given cooling capacity and requirements. Commercial enhanced tubes were employed to simulate real-life conditions. The results of the present analysis were compared with those obtained by HTRI software for verifying them. The results indicated that a reduction in the water pressure drop, which is associated with the short length of a tube, can be effected by decreasing the number of tube passes and increasing the number of tubes and the tube diameter. However, using a large number of tubes with smaller diameters can reduce the capital cost because the tubes are short. The reduction of the capital cost is due to the fact that a small-diameter tube has low internal thermal resistance and hence contributes to a decrease in the overall thermal resistance per unit length.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.1
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• pp.188-195
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• 2002

To investigate the degradation of mechanical properties induced mainly by neutron irradiation, the tensile tests were conducted from room temperature to 300\\`c using the irradiated and the unirradiated Zr-2.5Nb pressure tube materials. The irradiated longitudinal and transverse specimens were collected from the coolant inlet, middle, and outlet parts of M-11 tube which had been operated in Wolsung CANDU Unit-1 and exposed to different operating temperatures and irradiation fluences. The different tensile behavior was characterized not by the fluences of irradiation but by the tensile loading direction. The transverse specimen showed the higher strength and lower elongation than those of the longitudinal one. It was believed that these phenomena resulted from the microstructure anisotropy caused by the extrusion process. The increased strength hardening and decreased elongation embrittlement of the irradiated material were compard to those of the unirradiated one. While the tensile strength of the inlet was higher than that of the outlet, the elongation of the inlet was lower than that of outlet. Considering the operation condition, it was proposed that the operating temperature could be a more effective parameter than the irradiation fluence for long-time life. Through the TEM observation, it was found that while the a-type dislocation density was increased, the c-type dislocation was not changed in the irradiated. The fact that the higher dislocation density was sequentially distributed over the inlet, the middle, and the outlet parts was consistent with the distribution of the tensile strength.

• Journal of Korean Clinical Nursing Research
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• v.23 no.2
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• pp.151-160
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• 2017

Purpose: The purpose of this study was to evaluate the effects of oral stimulation interventions on the transition from tube to oral feeding in preterm infants through systematic review. Methods: The randomized clinical trials published between 1980 and 2015 were searched using domestic and international databases, and five randomized studies were selected for this study. The quality of study was assessed by assessment tool from the SIGN and meta-analysis was performed using the Cochrane Review Manager software Version 5.3 (RevMan). Results: Oral stimulation intervention in preterm infants decreased the transition time from tube to oral feeding (Post Menstrual Age, Day of life). Especially, a significant medium effect size was found in the number of days needed on the transition (ES=-4.95, p=.02). The oral stimulation intervention also had a significant large effect on the length of stay at hospital (ES=-8.33, p<.001). Conclusion: Based on the findings, oral stimulation interventions could be useful to facilitate the transition from tube to oral feeding in preterm infants in terms of reducing the length of stay at hospital and the number of days needed on transition.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.1
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• pp.17-24
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• 2003

In this paper, a high efficiency leakage transformer for neon tube is developed to improve its power factor, to reduce its core loss and weight by using a technique of shape optimization and grain direction of non-oriented silicon steel strip. A protection circuit is designed for all types of neon transformer loaded with one or more neon tubes. Whenever the neon tube fails to be started up or comes to the life end, or encounters faults with open-circuits at the output terminals of the neon transformer, the electronic type protection circuit will be initiated to avoid more critical hazards. These neon transformers need a electronic type protection circuit to prevent from current stresses on circuit components by neon tube fail. The input of the transformer is automatically cut on when the abnormal condition occurs, preventing waste of no-load power.

• Journal of the Korean BIBLIA Society for library and Information Science
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• v.32 no.1
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• pp.415-442
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• 2021

This study analyzed YouTube beauty videos that focus on makeup for teens, based on the assumption that the main viewers of the videos are teens. Through looking at the interaction between beauty information providers and receivers, communication among information receivers, and the way people participate in comment thread, the study examined how teens engage in social media. Many teens who posted comments on YouTube beauty videos praised and envied the beauty of beauty gurus, and tried to connect with them. The comment thread shows that teens answered to each other's questions on makeup tips, shared thoughts and experiences on issues around teen wearing makeup, which helped them build a sense of community, and broaden their views on the way of life. Also observed was power dynamics among youth, such as lecturing or verbal abuse against children and pre-teens by older teens.

• Aerospace Engineering and Technology
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• v.13 no.1
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• pp.10-19
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• 2014

We designed bearingless rotor hub system which replace mechanical hinge/bearing with composite beam component and conducted fatigue analysis for flexbeam and torque tube. Extension/bending/torsional stiffness was calculated from 2D section analysis using VABS and 2D section structure analysis was applied for strain calculation. S-N curve of each composite material was generated using Wohler equation and fatigue analysis was conducted on weakness section which was decided from static structure analysis. CAMRAD II was used for load analysis and load analysis result was applied HELIX/FELIX standard load spectrum to generate bearingless rotor system load spectrum which was used fatigue safe life analysis.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.2
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• pp.236-242
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• 1989

In order to investigate the effects of hot corrosion on the creep rupture properties and creep life of 304 stainless steel being used as tube materials of heavy oil fired boiler, the creep rupture tests were carried out at temperature 630.deg.C, 690.deg.C and 750.deg.C in static air for the specimens with or without coating of double layer corrosives according to the new hot corrosion test method simulating the situation commonly observed on superheater tubes of the actual boiler. The double layer corrosives are 85% V$_{2}$O$_{5}$ + 10% Na$_{2}$So$_{4}$ + 5% Fe$_{2}$O$_{3}$ as the inner layer corrosive being once melted at 900.deg. C and crushed to powder, and 10% V$_{2}$O$_{5}$ + 85% Na$_{2}$SO$_{4}$ +5% Fe$_{2}$O$_{3}$ as the outer layer corrosive. As results, in the specimen coated with the double layer corrosives, the rupture strength was extremely lowered and showed a large difference each other. The rupture ductility also lowered remarkably as a result of the brittle fracture mode due to hot corrosion. These results indicate that hot corrosion could essentially alter the creep fracture mechanism. From the metallographic observation, it was clarified that the rupture life of 304 stainless steel subjected to hot corrosion was chiefly determined by the behavior of the aggressive intergranular penetration of sulfides.des.

• Journal of the Korean Wood Science and Technology
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• v.35 no.1
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• pp.11-16
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• 2007

This study was carried out to investigate the effect of Vapor-dam treatment on drying drying rates, prevention of checks and V-shaped split during air circulating oven drying bamboo (Phyllostachys pubescens Mazel et Z) tube. It was shown that the drying time from green to around 7~8 % of moisture content was required less as drying schedule was more severe, and distinctly dominated by the drying rate during the initial drying stage. Area shrinkages in cross section and thickness shrinkages measured during air circulating oven drying test were very large. Surface checks and V-shaped splits were occurred in untreated samples just after the beginning of drying, while sixty seven percentages of all the Vapor-dam treated samples could be produced without drying defects. The V-shaped splits occurred in the Vapor-dam treated samples were influenced more by the sealing of the vapor evaporation through the cross section than drying schedule.

• Journal of Ocean Engineering and Technology
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• v.12 no.2 s.28
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• pp.65-70
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• 1998

In this report, the creep properties and creep life estimation by Larson-Miller Parameter(LMP) Method for 2.25Cr1Mo steel to be used as power plant tubes or other components were presented at the high temperatures of 500, 550, and $600^{\circ}C$. It was confirmed experimentally and quantitatively that a creep life estimation equation at such various high temperatures was well derived by LMP and could be used very effectively within the creep life of 10$^3$ hours, but very unreliable and even dangerous for design in a long term of creep life such as 10$^4$ or $10^5$ hours.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.489-496
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• 2010

The power generation and chemical industry have been subjected to further material degradation with long term operations and need to predict the remaining service life of components, such as reformer tube and steam turbine rotor, that have operated at elevated temperatures. As a non-destructive technique, replication method with reliable metallurgical life and microstructural soundness assessment has been recognized with strongly useful method until now. Developments of this method have variously accomplished by new quantitative approach, such as carbide analysis, with A-parameter and grain deformation method. An overview of replication, some new techniques for material degradation and life assessment were introduced in this paper. Also, on-site applications and its reasonableness were described. As a result of having analyzed microstructure by replication method, carbide approach was quantitatively useful to life assessment.