TEION KOGAKU (Journal of Cryogenics and Superconductivity Society of Japan)

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To construct a calculation model of flow loss in a helical-type seawater magnetohydrodynamics (MHD) power generator, it is important to elucidate the effects of the rotation number, the pitch length and the inner diameter of the helical wall on the pressure distribution and flow loss. The pressure distribution and flow loss in experimental devices constructed to model generators with a helical wall made of polyvinyl chloride with an outer diameter of 100 mm, inner diameters of 10, 20 and 30 mm, pitch lengths of 30, 37.5 and 45 mm and rotation numbers of 3, 5 and 7 were measured systematically. The effect of the rotation number on flow loss was small at flow rates of 20 m³/h or less and relatively large at flow rates of 30 and 40 m³/h. The effect of the pitch length was small at flow rates of 20 m³/h or less and relatively large at flow rate of 28 m³/h. The effect of the inner diameter was small at flow rates of 20 m³/h or less and relatively large at flow rates of 30 and 34 m³/h. The pressure drops in the vicinity of the entrance and / or the exit were the main causes of the disagreement in the flow loss between the experimental and computed values. The equations for the coefficient of entrance flow loss and exit flow loss were modified on the basis of the experimental data.

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The microstructure of YBa₂Cu₃O_7-δ (YBCO) superconducting wire with textured Cu substrate was investigated using an electron back scattering pattern (EBSP) and transmission electron microscopy (TEM). The structure of this wire is YBCO/CeO₂/YSZ/CeO₂/electro-plated Ni/textured Cu/SS. The YBCO film with J_c of 3.2 MA/cm² was prepared for this observation. The crystallographic orientation relationship between the Ni layer and the Cu layer was investigated. The good cube-on-cube epitaxy including the position and the direction of the grain boundaries were confirmed. In addition, the clear layered structure and fact that there were no out-of-phase components were confirmed. From the electron beam diffraction, the crystallographic orientation relationship was confirmed as YBCO(006)//CeO₂(002)//YSZ(002)//CeO₂(002)//Ni(002) and YBCO(200)//CeO₂(220)//YSZ(220)//CeO₂(220)//Ni(200). From the results of energy dispersive X-ray spectrometry (EDS), the diffusion of Ni and Cu were confirmed. The need to optimize the Ni-layer thickness was suggested.

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