The fabrication method where a duplex alloy is mechanically reduced to wires or tapes by simple metallurgical processes, that is rolling, swaging and wire-drawing after ingot-casting is an approach for producing composite materials. The composite produced by this method is called the in situ formed composite. This process was first applied to the production of superconducting materials by Tsuei and thereafter many works have been carried out extensively. This in situ formed superconducting composite has following characteristics. (1) Aligned superconducting filaments are fine but discontinuous. (2) The strength of composites is relatively high. (3) The superconducting properties, especially Jc, are stable against stress. The recent improvement of the fabrication method enables to produce the in situ formed composites with a large volume fraction of Nb3Sn filaments. Such composites show good superconducting properties with an overall Jc of 106A/cm2 at 4.2K and O field, which is comparable to that of the commercial Nb3Sn composite. Although the possible mechanisms of superconductivity in the in situ formed superconducting composite are considered to be filament effect, proximity effect and the direct contact of superconducting filaments, the latter two mechanisms will become important with increment of the volume fraction of superconducting filaments. More work remains to be done in improving Jc at high field and the stress effect of Jc.
In September 1978, production of liquid hydrogen was started on industrial scale (730l/hr) in our country in order to meet the increasing demand for the space development field. Nowadays, Japan has occupied a position comparable with Europe for supplying liquid hydrogen in commercial base. In this paper, the actual state of LH2 storage and transportation systems is introduced, and especially our experiences for LH2 transportation are described.
Transition boiling is the least studied field of boiling. During the last few years advances in cryogenic technology stimulated the interest to the transition and there appeared a number of works, in which boiling curve was investigated under conditions of independent changes of Tc. Transition from nucleate to film boiling at independently varying temperature differences is a smooth, gradual and continuous process and this hinder reliable fixation of actual boundaries of the processes, characteristic for the transition region. In the works mentioned in this paper, special attention was paid to the effects of geometry, surface roughness, gravitational acceleration, pressure and subheating in boiling of various liquids upon relations between heat flux density and temperature difference and upon the position of boundaries in the transition boiling region.
Solution of inverse problem of heat conductivity for conditions which are of practical interest for boiling of cryogenic liquids inside tubes, the methal representing a generalization of one-dimentional Buggraff method in case of two spatial coordinates is used. In this paper two-dimentional equation of instable conductivity for a double infinitive cylinder with an ideal heat contact on the interface of two kinds of materials with constant heat physical characteristics. In practice this case is applied to cool down of pipelines with low conductivity coatings by cryogenic liquids.
We reported in a previons paper that, in a wide aperture liquid helium dewar, the largest facter among heat losses is the radiant heat input from the top surface and that it can be reduced by painting aquadag on the inner wall. In this paper, we investigate several kinds of surfaces instead of aquadag as durable treatment, for example, sulfarized, oxidized or sandblasted surface. In the case of sandblasted surface, its rough surface was approximated by sine-wave and a computer simulation was applied to the thermal analysis.