A coating with surface-crack structures was observed to promote boiling heat transfer. An acrylic resin that develops cracks on its surface through natural drying was applied to a copper plate; subsequently, quenching experiments using liquid nitrogen were conducted. As a result, boiling heat transfer enhancement was observed across almost the entire temperature range during the cooling process, and the cooling time was considerably shortened. Near room temperature, complete film boiling disappeared, and an increase in heat flux was observed compared with the bare surface. In addition, the critical heat flux increased to approximately twice that of the bare surface. It is highly likely that the enhancement of surface wettability because of surface roughness contributed to boiling heat transfer enhancement.

This study discusses the electromagnetic characteristics of superconducting magnetic bearings (SMBs) using ring-shaped permanent magnets (PMs) and laminated high-temperature superconducting tapes. The two ring-shaped PMs of different magnetization structures are applied for SMBs to compare thrust electromagnetic force and rotation loss. The measurement results of maximum thrust magnetic force using axial magnetization ring-shaped PM reached almost 60 N. Furthermore, the rotation loss characteristics indicated that the rotation loss with the SMB was less than 1.5 W in the range of 1,000–1,600 rpm.