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Electrical Relaxations of Amorphous xKNbO3-(1-x)SiO2 (x = 0.33, 0.5, 0.67, 0.8)
송철호,양용석,진근영,최현우,김맥 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
We have investigated the relaxation behavior for amorphous xKNbO3 . (1 . x) SiO2 (x = 0.33, 0.5, 0.67, 0.8). Samples were prepared by using a twin-roller quenching method, and electrical measurements were carried out in the frequency range from 102 Hz to 1.5 × 107 Hz at a heating rate of 2 K/min. The frequency dependence of the electrical data was analyzed in the frameworks of the electrical modulus formalism and the universal power law. The activation energies obtained from the distribution of the relaxation time of the electrical modulus and the power law were found to become smaller with increasing KNbO3, indicating that the activation energy is an appropriate parameter for describing the relaxation mechanism in the glass region. We have drawn scaling plots for the electrical conductivity obtained using the modulus and the power law methods. We have investigated the relaxation behavior for amorphous xKNbO3 . (1 . x) SiO2 (x = 0.33, 0.5, 0.67, 0.8). Samples were prepared by using a twin-roller quenching method, and electrical measurements were carried out in the frequency range from 102 Hz to 1.5 × 107 Hz at a heating rate of 2 K/min. The frequency dependence of the electrical data was analyzed in the frameworks of the electrical modulus formalism and the universal power law. The activation energies obtained from the distribution of the relaxation time of the electrical modulus and the power law were found to become smaller with increasing KNbO3, indicating that the activation energy is an appropriate parameter for describing the relaxation mechanism in the glass region. We have drawn scaling plots for the electrical conductivity obtained using the modulus and the power law methods.
Ionic Conductivity in Mixed Alkali-Borate Glasses
김맥,양용석,송철호,진근영,최현우,임영훈 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
The temperature- and frequency-dependent ionic conductivity in (Li1.xNax)2B4O7 (LNBO), (Li1.xKx)2B4O7 (LKBO) and (Li1.xRbx)2B4O7 (LRBO) glasses have been investigated using Xray diffraction (XRD) and an impedance/gain-phase analyzer. We have specifically focused on the dielectric properties in frequency and temperature domains, and those have been analyzed by using a power law. We have found that the dc conductivity value decreases with heavy elements on mixing the alkali ions in the glass structure. For the LNBO, LKBO and LRBO glasses, the mixed alkali effect is observed to become stronger with decreasing temperature and increasing mismatch of the element size. The concentration dependence of the activation energy of the dc conductivity is characterized in the framework of reverse-Monte-Carlo-produced structural models in combination with the bond-valence technique.
전산유체역학 해석에 기반한 20㎾급 도립형 횡류수차의 제작 및 성능 실증
함상우(Sangwoo Ham),최지웅(Ji-Woong Choi),정창호(Changho Jeong),김태윤(Taeyun Kim),최상인(Sangin Choi),진근영(Glenn Young Jin),이정완(Jeong Wan Lee),하호진(Hojin Ha) 한국기계가공학회 2021 한국기계가공학회지 Vol.20 No.2
The cross-flow turbine is one of the most famous and widely used hydraulic power systems for a long time. The cross-flow turbine is especially popular in many countries and remote regions where off-grided because of its many benefits such as low cost, high efficiency at low head, simple structure, and easy maintenance. However, most modern turbines, including the cross-flow turbine, are unsuitable for the ultra-low head situation, known as less than 3m water head or zero head with over 0.5m/s flow velocity. In this study, we demonstrated a 20kW class inverted-type cross-flow turbine’s performance. First, we reevaluated our previous studies and introduced how to design the inverted-type cross-flow turbine. Secondly, we fabricated the 20kW class inverted-type cross-flow turbine for the performance test. And then, we designed a testbed and installed the turbine system in the demonstration facility. In the end, we compare the demonstration with its previous CFD results. The comparing result shows that both CFD and real model fitted on guide vane angle at 10 degrees. At the demonstration, we achieved 42% turbine efficiency at runner speed 125 RPM.