In thermoacoustic theory, which represents thermodynamical and fluid mechanical phenomena of oscillating fluid in flow channels, remarkable advances have been made in the last several years. Then it is found that the theory and its numerical calculations are useful for the understanding and analysis of the phenomena which occur in the working space not only of regenerative refrigerator (e.g. Stirling, G-M and pulse tube refrigerator) but also of the resonance tube refrigerator and the Stirling engine. This paper describes the easier understanding of the basic idea of the thermoacoustic theory and the physical images of the appeared quantities in the theory by means of graphical representation with keeping the accuracy of the discussion. This theory consists of two steps. The first step is to derive the quasi-local formulas of energy transfer and conversion for oscillating fluid by considering the heat transfer between the fluid and the wall of the flow channel in a cross sectional area. The second step is to derive the formulas of spatial variation for the axial direction based on the quasi-local formulas. In this paper, only the first step is treated and the derivation process of the formulas by visual thermodynamical diagrams is shown. The quasi-local formulas, which are derived from the complex equations in the original treatment, are diagrammatically derived from the combination of components of the corresponding complex values. The thermoacoustic theory provides us with a new classification for heat transfer and work losses in a regenerative refrigerator by expressing the phenomena observed from oscillating (i.e. Lagrangian view point), then it is expected that their intrinsical and physical meaning are well understood and to be effectively used for the design and improvement of actual devices and instruments.
Since the discovery of high Tc oxide superconductors, intensive studies have been made on forming thin films. Not only application for cryoelectronics but also physical study requires welldefined films with a smooth surface and the desired crystalline orientation. So far, several methods such as sputtering, vapor deposition, pulsed laser deposition and chemical vapor deposition have successfully been used to produce oxide superconductor films with epitaxial growth. Oxidation is a critical condition to obtain good quality films. In addition, peripheral technologies such as etching, electrode formation and protection coating are considered to be important for devices such as Josephson junctions, SQUIDs and infrared radiation detectors.
A computer code based on the two-fluid model is developed to analyze steady state heat transfer of superfluid helium (He II) flow. Numerical results for temperature profile and heat transport by internal convection are in good agreement with experimental data in the literature. Comparisons are made between the two-fluid model and the “simplified model”; explanation from the mathematical point of view is provided to validate the latter. Transient analysis with the simplified model is also conducted.
This paper summarizes the results of the second critical current measurement intercomparison of Nb3Sn wire sample implemented in the framework of VAMAS (Versailles Project on Materials and Standards) and discusses the origins of data scatters reported by the participants. In the second intercomparison, measurement conditions were strictly specified, particularly in terms of sample strain. Sample B used in the first intercomparison was used as a single sample for the second intercomparison. Variation coefficient of critical current at 12T was greatly reduced from 8.0% in the first intercomparison to 2.2%, probably because sample strains were well minimized among laboratories within the variation of 0.03%. Based on the results of critical current measurements on the NbTi sample as well as those of complementary measurements, it was found that, in addition to the sample strain, uncertainty in magnetic field determination and sample homogeneity substantially contributed to the variation coefficients of the critical current in the second intercomparison.
The positron annihilation method has been applied to evaluate unoccupied space in epoxy aiming at the design of the molecular structure for cryogenic use. To confirm the model in which molecular free space is needed in the epoxy for cryogenic use, the molecular weight between crosslinkings in epoxy was changed. The increase of molecular weight between crosslinkings brought an increase of fracture toughness even at liquid helium temperature and the model was found to be confirmed. The increase of molecular weight between crosslinkings was also found to decrease the 3rd lifetime of positrons. It suggested that the epoxy main chains were folded and this was confirmed by the molecular mechanical calculation.