Abstract
Effects of artificial holes on the cooling efficiency of single grain YBCO bulk superconductors were studied. Single grain YBCO bulk superconductors without artificial holes, with six 2.4 mm holes and six holes filled with Bi-Pb-Cd-Sn metal solder were fabricated by a top-seeded melt growth process for powder compacts with/without holes. Simulation for the cooling rate to a liquid nitrogen temperature (77 K) of YBCO samples was carried out using a finite element method (FEM) and the results are compared with the actual cooling rates of samples in liquid nitrogen. The simulated cooling times for the YBCO sample without holes, with six holes and with six holes filled with the metal solder were 80, 47 and 75 sec. respectively, which are similar to the actual cooling times of 84, 52 and 78 sec. estimated for the same samples cooled in liquid nitrogen. The shorter cooling time of the sample with artificial holes are attributed to the increased surface areas associated with the presence of artificial holes. The metal filling into the holes did not give any remarkable effect on the cooling efficiency.
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