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[en] A superconducting magnetic bearing is a dynamic system, which undergoes vibrations at various frequencies during its operation. In this study, we investigated the free vibration frequency modes of a permanent magnet (PM) levitated over a high temperature superconductor (HTS) where the vibration was provided by the seismic activities of the earth. The amplitude of the vibration was less than 1 μm as measured by a vibrometer. A disk shaped PM was levitated over a melt-textured HTS YBCO (yttrium barium copper oxide). The experimental setup was adopted to do the fast Fourier transform analysis of the vibration characteristics of the levitated PM. A cross-coupling between the vibration frequency modes of vertical, lateral and angular is observed in all respective directions for any particular vibration frequency measurement. The results indicate that all the vibration modes are actually the combination of the pure vibration frequency modes. The theoretical predictions based on the frozen-image concept show that the ratio of the vertical to lateral stiffness should be higher than 2 in the dynamic case, which is observed experimentally
[en] The behavior of the force between a permanent magnet (PM) and a high temperature superconductor (HTS) was tested with the frozen-image model based on flux pinning. It was found that the associated dipole moment assumptions of the method of the frozen image underestimate the force somewhat; thus a quadrupole moment analysis is proposed. The radial and drag forces associated with the rotation of the PM levitated above the HTS were measured by using a force transducer and by means of a cantilevered beam technique. The radial force was found not to be dependent on the radial direction, and the least radial force was found to be periodic with an angular displacement during the slow rotation of the PM relative to the HTS. The periodicity behavior of the force is attributed to the geometric eccentricity from the magnetization distribution of the PM and HTS. The drag force associated with the torsional stiffness of the levitated PM during the low and high rotational speeds was incorporated with the data from the literature.
[en] The future trends of the industry require major renovations in the infrastructure of transmission, distribution, and storing of generated energy. With the increased use of renewable energy across the globe, energy storage (ES) systems have started to play a prominent role in shaping the future of the ES market. However, because of the uneven distribution of the renewable energy throughout the world, more emphasis must be made to the integration of power grids with the ES devices to utilize the excess power more effectively. In this paper, a study is performed regarding the integration of a hybrid system, consisting of a lithium-ion battery (LIB) and superconducting magnetic energy storage (SMES), into an interconnected microgrid operation. The structure of a microgrid is explained by analyzing the selected battery (LIB) and voltage source converter (VSC)-based SMES unit via MATLAB & Simulink. Finally, the voltage waveforms are compared and discussed in detail.
[en] Highlights: • Experimental analysis of designed heat exchanger performed by using Taguchi method. • Reynolds number is most effective parameter for Nusselt number and friction factor. • The routers with winglet are more effective than without in terms of heat transfer. • Staggered sheet layout configuration of fins are more effective than the inline. • Among staggered sheet layout the most effective is hexagonal router without winglet. - Abstract: This study consists of experimental heat transfer analysis of a cross flow forced convection heat exchanger having rectangular duct channel with different tubular routers (flow pin-fins). The pin-fins are placed at the top and bottom plates periodically and perpendicular to the flow direction and they are structured in-line and staggered sheet layout. The pressure drop and heat transfer characteristics of the heat exchanger with heat recovery unit are investigated for certain Reynolds number interval in different temperatures and the flow rates of working fluids. To analyze the heat transfer properties of the designed heat exchanger the Taguchi method with L25 orthogonal array is used. The factors and levels of performance characteristics are examined individually by using the signal-to-noise ratios and analysis of variance (ANOVA) methods for various geometries and optimum condition. The thermal performance analysis of the heat exchanger is accomplished in terms of effectiveness-number of transfer unit (ε-NTU) method. The results indicated that the model having the best thermal performance is hexagonal pin-fins. The second best model is determined to be square-angle pin-fins configuration. The effect of the heat transfer and pressure drop are also discussed in terms of various fin geometries via obtaining the correlations of Nusselt number, friction factor and Colburn factor as a function of Reynolds number.