An experimental study of critical heat flux in non-uniformly heated vertical annulus under low flow conditions

An experimental study on critical heat flux (CHF) has been performed in an internally heated vertical annulus with non-uniform heating. The CHF data for the chopped cosine heat flux have been compared with those for uniform heat flux obtained from the previous study of the authors, in order to investigate the effect of axial heat flux distribution on CHF. The local CHF with the parameters such as mass flux and critical quality shows an irregular behavior. However, thetotal critical power with mass flux and theaverage CHF with critical quality are represented by a unique curve without the irregularity. The effect of the heat flux distribution on CHF is large at low pressure conditions but becomes rapidly smaller as the pressure increases. The relationship between the critical quality and the boiling length is represented by a single curve, independent of the axial heat flux distribution. For non-uniform axial heat flux distribution, the prediction results from Doerffer et al.’s and Bowring’s CHF correlations have considerably large errors, compared to the prediction for uniform heat flux distribution. KeyWords : Critical Heat Flux, Heated Vertical Annulus, Low Mass Flux, Wide Range Pressure, Non-uniform Heating, Effect of Axial Heat Flux Distribution, Boiling Length     

New type of miniaturized optical range-sensing methods RORS and RORST

Two types of miniaturized optical range-sensing methods have been developed. The first is called RORS (Riken Optical Range-Sensing Scheme). In this method, a mirror tunnel is first placed between an objective lens and an object to be measured; a bright spot is then projected onto the object through the objective lens. This spot is observed through the objective lens after reflection with the mirror tunnel, and range information is determined by the triangulation. The width of an optical system can be reduced remarkably smaller than the effective base line length of the triangulation. Therefore, it is suitable to miniaturize a range-sensing system such as an optical stylus and a proximity sensor. The second method, RORST (Riken Optical Range Sensing Method for Surface Tracing), projects an axially symmetrical light sheet onto an object and a ring pattern is produced. The ring pattern image is then projected onto the observation plane by the objective lens, radii of the ring pattern image for different azimuths are detected, distances corresponding to the specified azimuths are determined by the triangulation, and thus the information of partial inclination can be obtained.     

Formation of Ti diffusion barrier layers in Thin Cu(Ti) alloy films

In order to study a formation mechanism of thin Ti-rich layers formed on the surfaces of Cu(Ti) wires after annealing at elevated temperatures, the 300-nm-thick Cu(Ti) alloy films with Ti concentration of 1.3 at.% or 2.9 at.% were prepared on the SiO₂/Si substrates by a co-sputter deposition technique. The electrical resistivity and microstructural analysis of these alloy films were carried out before and after annealing at 400°C. The Ti-rich layers with thickness of ∼15 nm were observed to form uniformly both at the film surface and the substrate interfaces in the Cu(2.9at.%Ti) films after annealing (which we call the self-formation of the layers) using Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). Both the resistivities and the microstructures of these Cu(Ti) films were found to depend strongly on the Ti concentrations. The resistivities of the films decreased upon annealing due to segregation of the supersaturated Ti solutes in the alloy films to both the top and bottom of the films. These Ti layers had excellent thermal stability and would be applicable to the self-formed diffusion barrier in Cu interconnects of highly integrated devices. The selection rules of the alloy elements for the barrier self-formation were proposed based on the present results.     

Electrical conductivity of yttria-stabilized zirconia single crystals

The electrical conductivities of YSZ single crystals with various compositions covering FSZ and PSZ regions were measured by a complex impedance method and a four-probe a.c. method. The conductivities changed significantly as a function of composition. A simple conduction model for PSZ showed that the tetragonal phase is a good oxygen ionic conductor having an activation energy for motion of about 0.8 to 0.9 eV. It is promising for low temperature application of a solid state electrolyte.     

Railgun pellet injection system for fusion experimental devices

A railgun pellet injection system has been developed for fusion experimental devices. Using a low electric energy railgun system, hydrogen pellet acceleration tests have been conducted to investigate the application of the electromagnetic railgun system for high speed pellet injection into fusion plasmas. In the system, the pellet is pre-accelerated before railgun acceleration. A laser beam is used to induce plasma armature. The ignited plasma armature is accelerated by an electromagnetic force that accelerates the pellet. Under the same operational conditions, the energy conversion coefficient for the dummy pellets was around 0.4%, while that for the hydrogen pellets was around 0.12%. The highest hydrogen pellet velocity was 1.4 km s⁻¹ using a 1 m long railgun. Based on the findings, it is estimated that the hydrogen pellet has the potential to be accelerated to 5 km s⁻¹ using a 3 m long railgun.     

57Fe and119Sn conversion electron Mössbauer studies of Fe-Sn phases on tinplate

⁵⁷Fe and¹¹⁹Sn conversion electron Mössbauer spectrometry has been applied to the investigation of the compositional variations of the Fe-Sn intermetallic alloy produced at the surface of 90 nm thick tin electrodeposited steel by the thermal treatment. It was confirmed that the fully alloyed layer of FeSn₂, FeSn + FeSn₂, FeSn, FeSn + Fe₃SnC and Fe₃SnC was formed by the thermal treatment for 30 min at 300, 400, 500, 600 and 700° C, respectively, and that the thickness of the Fe-Sn layer increased with the elevation of temperature.     

Control strategy for an intelligent mobile vehicle

In this paper recent research into operating an intelligent mobile vehicle (denoted MV) is presented. A complex control procedure, having a two-input and twooutput fuzzy controller as kernel, is used. The inputs to the fuzzy controller are provided by a charge-coupled device (CCD) camera which transforms information on special objects by using an image processor. The MV is capable of tracking objects, searching for objects in space and recognizing a traffic signal. Results of laboratory testing are presented.