The present paper gives the results of the investigation of transition boiling and film boiling crisis. The investigation of transition boiling and film boiling crisis is now of great importance for many fields of science and engineering. These processes are realized in the cryogenic systems. The knowledge of transition boiling law is the basis for the calculation of superconducting device stability. However, the transition boiling remains till now one of the least explozed section of the heat transfer theory. P. Berenson, V. G. Pronko, K. Nisikawa, V. G. Grigoryev and a number of other Soviet and foreign scientists, up to now, have made a contribution to the study of boiling. A certain experimental material accumulated must be generalized. We have carried out a transition boiling complex study combining the development and analysis of theoretical models and the experimental investigation of physical mechanism of heat transfer process and correlations.
In order to study effects of irradiation at low temperature on insulating materials of superconducting magnets, flexural and impact tests are carried out at 4.2K without warmup after low temperature irradiation for several fiber reinforced plastics. The used materials are glass fiber reinforced epoxies and polyimide, and carbon fiber reinforced epoxies. After irradiation of 1.1×109rad, the reduction in flexural strength of G-10 CR is about 70% and that of G-11 CR about 25%. No change are observed in strength of glass fiber reinforced polyimide by low temperature irradiation. Other kinds of glass fiber reinforced epoxies show a reduction in strength but the flexural strength of carbon fiber reinforced epoxies increases a small by irradiation. Irradiation effect of these materials on impact value is similar to that on flexural strength.
A single layer race track magnet with a large Nb3Sn conductor has been constructed and tested in order to obtain engineering information on fabrication of a 10T multishell dipole magnet. A bronze processed Nb3Sn monolithic wire is used in the wind and react method. The cross section of the conductor is 2.3×6.0mm2 and the critical current is 4.60kA at 10T and 4.2K. The coil has an inner width of 25mm and an outer width of 181mm with a thickness of 6mm. The length of the straight section is 800mm in the total length of 956mm. The number of turns is 30. Mica glass tapes are sandwiched as insulators between the turns, and mica boards bonded with inorganic adhesives are used between the coil and two shielding iron plates. The coil has not been impregnated with epoxy resin after the heat treatment to keep good thermal contact with a liquid helium. After the construction of this magnet the following things became clear. A large current monolithic conductor can be wound in a small diameter as 25mm. The coil keeps its shape without an impregnation of epoxy resin. Though the conductor expanded longitudinally about 0.5% after the heat treatment, no local wire looseness and no stress concentration in the windings were induced. A mica glass tape withstands the heat treatment, which is surely useful as an insulator for a Nb3Sn magnet in the wind and react method. In the excitation tests, the magnet experienced two quenches at the currents of 5.32kA and 6.82kA, and reached 7.00kA which was the upper limit of our power supply. The central field is 4.65T at 7.00kA. The estimated critical current of the Nb3Sn conductor is about 11.83kA at 4.65T and 4.2K. Voltage tap