Abstract: In a heat transfer surface having cavity groups and restricted opening groups in an outer surface region, the cavity groups are composed of a plurality of rows of void strip members. The cavity strip members are arranged in parallel on a base member of the heat transfer surface and are laminated in one or more layers. Each strip member has a number of elongate cavities laterally arranged in parallel. The elongate cavities are closed at upper surfaces and have at both ends openings. The adjacent cavities in the same layer are communicated with each other by communicating portions each provided between the cavity strip members and by the openings. The restricted opening groups are formed on the upper surfaces of the communicating portions. The restricted opening groups render the communicating portions in one layer, the communicating portions in another layer and the outside to communicate with each another. The method of manufacturing such a heat transfer surface is also disclosed.

Abstract: A novel composite superconductor includes a superconducting material and a normal conducting material. The composite superconductor has a number of closely spaced grooves on a surface being in contact with a refrigerant, and a number of ridges spaced apart from each other by the grooves and having acutely tapered ends. The surfaces of the grooves and the ridges are coated with a thin film of metal or its compound having higher heat resistance than that of the surface of the composite superconductor. Consequently, a high critical heat flux in film boiling and a high cooling capability can be provided, thereby making it possible to decrease the sectional area of the normal conducting material, to increase the effective current density and to miniaturize the size of a magnet.