• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.6
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• pp.1307-1312
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• 2007

The flow characteristics of R-134a in a small diameter tube was investigated experimentally. An experimental apparatus was consisted of a magnetic gear pump, an evaporator, a sight-glass, a condenser and a measurement instruments. The sight-glass for flow pattern observations was located at the inlet and outlet of the evaporator. The experiment was carried out to show the flow characteristics of R-134a in a small diameter tube. Mass flux of refrigerants was ranged from 100 to 1000 $kg/m^2s$, the saturation temperature was $30^{\circ}C$. In the flow patterns during evaporation, the annular flow in a 2 mm inner diameter tube occurred at a relatively lower quality and mass velocity, compared to that in a 8 mm inner diameter tube. The evaporation flow pattern in a small diameter tube has been shown major deviations with the Baker, Mandhane and Taitel-Dutler's flow pattern maps but it was similar to the Dobson's flow pattern map.

• Journal of Energy Engineering
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• v.23 no.1
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• pp.46-57
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• 2014

This study analyzes whether the value-added structure of Korean wind power industry exhibits a virtuous cycle through the value chain(VC) within wind power firms and the value system(VS) among the wind power industries, using a regression analysis based on a survey about Korean wind power companies. According to the VC, the government's R&D support is analyzed to have contributed to an increase in the R&D investments of the wind power companies. An increase in corporates' R&D investments has led to an increase in corporates' R&D outputs, and in turn, induced a remarkable increase in the amounts of production. But an increase in production has not led to a decrease in the costs of production, not resulting in an increase in profit rates per sales amount. In addition, while an increase in profit rates is analyzed to have contributed to an increase in production, this did not induce further investments in corporate's R&D. The virtuous cycle of the value chain in Korean wind power firms is, therefore, analyzed to be weak. Next, the VS is analyzed by dividing the whole chain into the system group including rotor blades, gear boxes, and power generators, and the structure group, such as towers. Two groups are analyzed to have mutually positive effects in the processes of the government's support for corporates' R&D, corporates' investment in R&D, R&D outputs, and profit rates per sales amount. Such mutual positive effects are, however, not found in the processes of the amounts of production and the costs of production. These results demonstrates that the value system of Korean wind power industry is not completed. This study has a policy implication to need further efforts to create the virtuous cycle in the VC and VS of Korean wind power industry.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.596-603
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• 2020

'Electro-Mechanical Brake (EMB) is a novel braking system for automobiles and railway vehicles, and research in this area is actively underway. The current braking system for railway vehicles generates a braking force using a pneumatic cylinder, but the EMB system generates the force through a combination of an electric motor and gears. In this study, the design of an EMB system that meets the domestic standards was conducted through the finite element modeling and fatigue analysis of an eccentric rotating shaft-based EMB system capable of generating a high clamping force. At this time, to improve the accuracy of fatigue analysis, three types of fatigue test specimens, which were subjected to the same heat treatment as the materials used in the prototype, were produced, and the fatigue tests were performed for each material. The fatigue properties (S-N curves) were obtained from the fatigue test results for each material and reflected in the analysis model. The results of fatigue analysis confirmed that the design of the EMB prototype could satisfy the maximum commercial braking/relaxation of 530,000 times, which was the endurance life condition for domestic railway vehicles. In addition, based on this design, a prototype will be manufactured, and endurance testing will be completed to demonstrate the durability characteristics of the developed prototype.

• Journal of the Korean Geotechnical Society
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• v.23 no.7
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• pp.57-64
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• 2007

This study proposes a method to estimate drilling torque during ground boring with an aid of electrical energy required for rotating a boring-auger. Ground boring is commonly used in geotechnical engineering such as preboring precast pile installation, soil-cement grouting, ground exploration and so forth. In order to understand the correlation between required electrical energy to rotate the boring auger and the drilling torque, a small laboratory apparatus was designed and a pilot study was performed. The apparatus rotates common drill bits of $D=5{\sim}25mm$ in CBR specimens. The velocity of a bit is 19 RPM and predefined using a reduction gear which connects a main rotation axis to a 25 Watts AC electrical motor shaft. In the middle of drilling the motor current increments and the drilling torque were measured and the correlation between the current and the torque was obtained through linear square fits. Based on the correlation the acquired motor current during drilling was applied to predict the drilling torque in consequent testing and the prediction results were compared to the measured torque. The comparison leads a conclusion that the motor current during drilling using electrical power may be a good indicator to estimate/determine strength characteristics of the ground.