Heat-transfer characteristics of a viscoelastic turbulence past rectangular orifices were investigated in the context of the reduction effects of fluid elasticity on drag and heat transfer. To simulate the fully-developed channel flow through transverse orifices located periodically at intervals of 6.4 times channel height, we imposed periodic conditions at the upstream and downstream boundaries. To discuss the dissimilarity between the velocity and thermal fields, the molecular Prandtl number was set to be 1.0 and any temperature dependence of the fluid and rheological properties was not considered. In the present condition, the ratio of the reduction rates in drag and heat transfer was found to be 2.8:1.0, revealing that the present flow configuration is better than a smooth channel for avoiding the heat-transfer reduction. This phenomenon was attributed to the sustainment of the quasi-streamwise vortex downstream of the reattachment point despite the absence of strong spanwise vortices emanating from the orifice edge in the viscoelastic fluid. The longitudinal vortices behind the reattachment point caused a high turbulent heat flux and increase the local Nusselt number.
A structure analysis of Ti5Si3D0 .9 has been carried out to determine the deuterium trap sites by neutron powder diffraction with the Rietveld profile analysis. It is revealed that the deuterium atoms are located at octahedral (2b) sites surrounded by six Ti atoms in the crystal structure of Ti5Si3D0 .9, space group P63/mcm. Local vibration spectrum of hydrogen in Ti5Si3H0.83 measured by neutron inelastic scattering supports this result; the energy eigenvalue of the primary vibration mode is found at 7.53 kJ/mol (78 meV). The hole radius and the spring constant of the Ti-H(D) bond are discussed. (Received April 11, 1986) Keywords: Ti5Si3D0 .9, Ti5Si3H0.83, neutron diffraction, neutron inelastic scattering, deuterium location, hydrogen vibration Occupation sites and local vibration of hydrogen isotopes (H, D) dissolved in hexagonal metal lattice have not been clarified so well as those in bcc and fcc metals. A recent neutron elastic and inelastic scattering study revealed that hydrogen isotopes are trapped at tetrahedral interstices (t-sites) in ZrO0.4, while they occupy octahedral interstices (o-sites) in TiO0.3• It is worth noting that hydrogen isotopes can sit at either of the interstices in hexagonal metal lattices, and they tend to sit at o-sites rather than t-sites in the hexagonal lattice with relatively small dimensions; the lattice c=0.468nm and a=0.323, c=0.513nm, respectively.The present study is concerned with the determination of occupation site and of local vibration mode of hydrogen isotopes dissolved in a hexagonal compound Ti5Si3 with the Mn5Si3 type (or D88-type) structure.The
inch diameter AlN single crystals with the thickness of 0.025-2 mm were grown on SiC substrates by the sublimation method. Crystalline qualities were evaluated by X-ray diffraction and EPD measurements. The FWHM of X-ray rocking curve for (0002) reflection was 281 arcsec with 1.2-mm thick crystal and dislocation density measured by EPD was 1.6×106 /cm 2 with 0.8-mm thick crystal. These results were well consistent with the dependence of those properties on the thickness of the crystal, which was found in our previous work on 10-mm diameter crystals. According to this dependence, growing the thick AlN crystal on SiC substrates by the sublimation method is expected to lead to high-quality free-standing 1-inch AlN substrates.
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