Thermohydrodynamic description of adiabatic flow of He II, in which the high velocity region up to 100cm/s was studied, is given with a new-type mutual friction force. Experiments consist of various thermodynamic measurements and the NMR study of the motion of 3He atoms added to the system. There appeared various stages of the flow state of superfluid He II. Especially, there exist clearly two characteristic velocities vc1 and vc2. An interpretation of the results is given with the pinning-depinning model of quantized vortices, in which we made a conjecture that quantized vortices construct vortex-bundles in the presence of pinning-centers.
Effects of precracking temperatures and load on 4K fracture toughness, KIC, of tough 22Mn13Cr5Ni steel were investigated using an unloading compliance method. Compact tension specimens with a thickness of 25mm were precracked by fatigue at 298K, 77K and 4K. The stress intensity factor range, ΔKf, covered from 20 to 60MPa√m. The main results are as follows; (1) The experimental results showed that precracking temperatures and ΔKf hardly affected 4K-KIC of the 22Mn13Cr5Ni steel. (2) No α′ martensite was induced by precracking at all but ε martensite was induced at 4K. A subcritical crack growth started with a fracture of induced ε in 4K fracture toughness test. The dominant ε was not one induced by precracking but by fracture toughness test itself. Therefore the effects of ε by precracking at cryogenic temperature could be neglected. (3) Room temperature precracking produced a larger plastic zone than law temperatures. However its effect on 4K-KIC was very small because contraction of plastic zone could be expected and because ε was not induced at all.
A development of the H-II launch vehicle, which will put the 2-ton-class payload into geosynchronous orbit, is progressed by NASDA in Japan. A 910-kN-thrust LOX/LH2 rocket engine, LE-7 was to be developed as a first stage propulsion system of the H-II launch vehicle. In a first development phase of this engine, a short duration firing test facility feeding high pressurized propellant was needed to carry out the firing test of the combustion system components of this engine. This firing test facility has the thick wall runtanks for feeding high pressurized propellant to those components. In this paper, the cool-down time of the thick wall runtanks with a chill-down coil by using liquid nitrogen is analyzed in consideration of the heat transfer characteristics and the changes of fluid phase. Then, a calculation method estimating the cool-down time is presented. Experiments confirmed the estimating method in a relatively good agreement.
Superconducting NbN films prepared onto quartz and sapphire substrates by rf sputtering have been investigated on the growth and preferred orientation of grains with B1 structure, and on their upper critical field, Hc2. Fine columnar grains of B1 phase with a preferred orientation in the ‹111› direction perpendicular to the substrate surface are simply formed on quartz. NbN films deposited on the (1102) plane of sapphire have a 1, 500Å thick inital growth layer on which coarse columnar grains grow rapidly with the same preferred orientation as on quartz. The columnar diameter of B1 grains is somewhat affected by substrate temperature, Td, and increases with Td up to 600°C. When the Td exceeds 600°C, films contain B1 grains growing with a (200) preferred orientation. Higher values of Hc2 have been obtained for films deposited on quartz and, especially, the perpendicular critical field, Hc2⊥, appreciably increases with reducing the columnar grain diameter to -150Å. Depositions at higher gas pressures seem to produce a beneficial effect on the growth of small grains which yield an increase in Hc2.
Static thermal stability of the superconductors cooled by pool boiling has been examined in reference to Stekly's criterion, Maddock's equal area criterion and Wipf's MPZ (Minimum Propagating Zone) theory. No discussion on Stekly's criterion shall be done here because there are no disputable points left. Maddock's equal area criterion and Wipf's MPZ are both discussing the stability from the same point of view of unstable equilibrium. Nevertheless, the former leads to the maximum allowable current and the latter does not. Therefore, in the present paper, the relationship between Maddock's criterion and Wipf's MPZ and the physics underlying these theories are to be discussed firstly. Then an extensive sample calculation of MPZ is introduced for a realistic characteristic of pool boiling heat transfer which is very non-linear. Formulations have been general as far as they should.
An MF superconductor with ultra-fine continuous Nb3Al filaments has been fabricated successfully by the newly developed composite process, in which a composite consisting of a niobium matrix and a large number of Al-Mg alloy cores is cold-drawn into a wire with very fine Al-Mg filaments (about 0.1μm), and then heat treated at 650-1, 000°C to form Nb3Al continuous filaments by the diffusion reaction. The wire shows Tc of 15-16K, μ0Hc2 (4.2K) of 21-23T and Jc (4.2K, 10T) of 1-1.5×105A/cm2, which are as high as those of the practical Nb3Sn multilamentary wires.
In the superconductive lanthanum compounds La2-xAxCuO4 (A=Sr, Ca, Ba), divalent ions were substituted with monovalent Na, K and divalent Pb. Only the substitution with Na resulted in a superconductivity, and the critical temperature (Tc) is found to be 22.2K at the composition at La1.5Na0.5CuO4 reacted at temperatures between 880 and 890°C. In another superconductive compound LaBa2Cu3O7-y which has the same structure as YBa2Cu3O7-y, divalent Ba ions were partially substituted with Ca2+ and Sr2+. In the compound LaBaSrCu3O7-yTc deteriorates and two superconductive phases appear. On the contrary, in the compound LaBaCaCu3O7-y metalic behavior and a sharp transition in resistivity are found, i.e., its transition width (ΔT) is within 3K. Further, Tc is not much influenced by the sintering temperatures between 890 and 1, 050°C, and is reproducibly settled in between 74.7K and 77.4K. These results should be compared with those obtained in LaBa2Cu3O7-y, in which Tc largely depended on sintering temperature and T amounts to 13.4K.
Sintered oxide superconductors can carry only small transport current, while large closed shielding currents flow inside grains. In this report we demonstrate that an ac inductive method is useful for estimate of these current densities. It is shown that estimate of the critical current density in sintered materials from dc magnetization measurement contains a serious error. The history effect of the critical current density is also discussed.