Superconducting flywheel energy storage systems using superconducting magnetic bearings have been studied regarding the possibility of contributing to daily load leveling. To make the system feasible for practical application, the levitation force of the radial-type superconducting magnetic bearing must be enhanced. Therefore, we have come up with an idea to change the shape of the cross sections of the permanent magnet and yoke from the present rectangular form to a trapezoidal (or triangular) shape. We analyzed the levitation force in the case where such a permanent magnet and yoke are applied, and produced and actually measured the permanent magnet and yoke. Moreover, anticipating that the adopting the conventional Y superconductor assembly and Gd superconductor assembly, which has better characteristics than the former, would have an effect on levitation force enhancement, we produced these two types of superconducting bearing assemblies and actually measured them. We demonstrate that levitation force is enhanced when the permanent magnet assembly has a trapezoidal cross section and the Gd superconducting bearing assembly is used.
Superconducting flywheel energy storage systems using superconducting magnetic bearings have been studied for their feasibility to contribute to daily load leveling. To make the system fit for practical application, the levitation force of radial-type superconducting magnetic bearing must be enhanced. If the magnetic flux leaked outside of the permanent magnet can be induced internally to the furthest possible extent and the magnetic flux acting the superconductor can be increased, it is believed that the levitation force will be enhanced. Therefore, we introduced the idea of applying a Halbach permanent magnet, which produces a strong magnetic field almost totally on one side, to the permanent magnetic assembly. The magnetic field and levitation force in the case where a Halbach permanent magnet is applied were then analyzed. Based on the results of analysis, we have demonstrated that levitation force is enhanced when the above-mentioned Halbach permanent magnet is applied to a radial-type superconducting magnetic bearing.
The entropy flow is rearranged in accordance with the new thermoacoustic theory. The local entropy production rate for thermoacoustic phenomena is formulated. The entropy production rate due to the effective heat conduction and that due to the dissipation of the work flow are positive. The results of formulation are rewritten in terms of normalized amplitude and impedance. Some empirical facts related to the normalized impedance are qualitatively discussed.