Slush hydrogen is a two-phase solid-liquid cryogenic fluid consisting of solid hydrogen particles in liquid hydrogen. Compared to liquid hydrogen, the density is about 16% greater at a solid mass ratio (solid fraction) of 50%, and the cryogenic heat capacity (enthalpy) is about 18% higher. Various applications are anticipated, including fuel for reusable space shuttles, coolant for cold neutron generation, as well as the transport and storage of hydrogen as a clean energy source. At a solid fraction of within 50%, piped transport can be conducted in the same way as for normal fluids. This paper reports on the slush hydrogen technology in terms of the measurement of the density and the mass flow rate. (Translation of the article originally published in Cryogenics 44 (2004) 59-68)
HTS wires have been improved to the extent that they have practical properties, and various HTS coils have been designed and fabricated. One of the features of an HTS coil is high thermal stability against thermal disturbances. The minimum quench energy (MQE) of an HTS coil is several orders higher than that of an LTS coil. However, thermal runaway, which shows almost the same phenomenon as quenching observed in an LTS coil, is observed in a conduction-cooled HTS coil when the HTS coil is operated under a high load factor. Thermal runaway causes degradation of an HTS coil, so it is important to quantitatively evaluate the thermal runaway currents of a conduction-cooled HTS coil. This paper shows the thermal runaway evaluation test results for a conduction-cooled HTS coil wound with an Ag-sheathed Bi2223 wire.
In order to quantitatively evaluate the thermal stability of conduction-cooled HTS coils, thermal runaway currents of a conduction-cooled HTS single-pancake coil were measured at various temperatures and several cooling conditions, and numerically calculated using a calculus of finite differences. Calculated results were in good agreement with the experimental ones. A sensitivity analysis of thermal runaway currents for various physical values was also carried out. The thermal conductivity, specific heat and n-value of an Ag-sheathed Bi2223 wire do not significantly affect the thermal runaway currents of the coil. However, the critical current of an Ag-sheathed Bi2223 wire strongly affected the thermal runaway currents. Therefore, more precise critical current data should be prepared in the thermal stability analysis of conduction-cooled HTS coils.