Experimental study of heating fluid between two concentric cylinders with cavities

In this paper, we are concerned with the heating fluid in the annular space between two concentric cylinders where the inner cylinder with cavities is rotated and the outer cylinder is at rest. The effects of cavities of the inner cylinder on the heating fluid and the cavitation behavior are examined. We measured the flow rate, rotating speed of rotor, friction torque, temperature rise and pressure drop between inlet and outlet of this device. The flow rate of water ranged from 0.42×10^-4 to 4.59×10^-4 ma/s at the inlet. The friction torque and the quantity of heat of the inner cylinder with cavities were larger than the case of no cavities, and they increased as the rotating speed of inner cylinder increased. The efficiency was close to about 1 as the rotating speed of inner cylinder increased. The behavior of cavitation in the cavity on the surface of inner cylinder was discussed.     

Comparison between numerical simulation and visualization experiment on water behavior in single straight flow channel polymer electrolyte fuel cells

A relationship between a flooding and a cell voltage drop for polymer electrolyte fuel cell was investigated experimentally and numerically. A visualization cell, which has single straight gas flow channel (GFC) and observation window, was fabricated to visualize the flooding in GFC. We ran the cell with changing operation condition, and measured the time evolution of cell voltage and took the images of cathode GFC. Considering the operation condition, we executed a developed numerical simulation, which is based on multiphase mixture model with a formulation on water transport through the surface of polymer electrolyte membrane and the interface of gas diffusion layer/GFC. As a result in experiment, we found that the cell voltage decreased with time and this decrease was accelerated by larger current and smaller air flow rate. Our simulation succeeded to demonstrate this trend of cell voltage. In experiment, we also found that the water flushing in GFC caused an immediate voltage change, resulting in voltage recovery or electricity generation stop. Although our simulation could not replicate this immediate voltage change, the supersaturated area obtained by our simulation well corresponded to fogging area appeared on the window surface in the GFC.     

Microstructures and properties of die casting components with various thicknesses made of AZ91D alloy

In this paper, microstructures and properties of die casting components with various thicknesses made of AZ91D alloy have been investigated by means of scanning electron microscope (SEM), transmission electron microscope (TEM), high-resolution transmission electron microscope (HRTEM), etc. It is concluded that mechanical properties of the die casting components mainly depend on grain size of α-Mg phase. At the same time, however, the voids formed by entrapping air during die casting process have a remarkable detrimental effect on the mechanical properties. To what extent the effect is caused is determined by quantity, size and shape of the voids, which are related to the thicknesses and position of the component in die. Nanometer particles found on the wall of the voids are magnesium oxide compounds, which are formed when oxygen from the entrapped air reacts with magnesium during die casting process. The compounds have no obvious effect on the mechanical properties even though there is possibly volume change present to form other compounds in the course of the components’ being used.     

Effect of oxidizing agents on selenate formation in a wet FGD

In a coal combustion process, a considerable amount of selenium is captured in the wet FGD, where it is oxidized from selenite to selenate , which is difficult to remove. Diethyl-p-phenylene-diammonium (DPD) absorptiometric analysis and ion chromatography identified peroxodisulfate ion as the dominant oxidizing agent in the FGD liquor. Selenite was easily oxidized to selenate in the presence of and the oxidation was accelerated as the temperature increased. Addition of Mn²⁺ ion was found to be effective in controlling selenate formation. When Mn²⁺ ion was added, oxidized not selenite to selenate but rather Mn²⁺ to MnO₂, which captured some dissolved selenite.     

Conversion of Solution‐Derived Perhydropolysilazane Thin Films into Silica in Basic Humid Atmosphere at Room Temperature

Spin‐on perhydropolysilazane (PHPS) thin films were converted into mechanically hard silica thin films by an exposure to the vapor from aqueous ammonia. Infrared absorption and X‐ray photoelectron spectroscopic analyses were conducted to clarify the details of the PHPS‐to‐silica conversion and the nature of the silica thin film products. The PHPS‐to‐silica conversion was found to proceed rapidly between 2 and 3 h of exposure via a reaction‐limited process, where the refractive index and the pencil hardness greatly decreased and increased, respectively. Finally, the O/Si mole ratio close to 2 was achieved, which has never been realized in literature for PHPS‐derived silica thin films. It was also found that the condensation of Si–OH groups proceeds in films immediately after PHPS hydrolysis, which is similar to the base‐catalyzed hydrolysis–condensation reaction of silicon alkoxides. Although the silica thin films obtained had refractive indices similar to that of silica glass, high pencil hardness over 9H on Si(100) substrates, and O/Si mole ratios close to 2, it was concluded that they are nonidentical to silica glass, containing trace amounts of Si–OH and Si–H groups.     

Evaluation for sintering of electrocatalysts and its effect on voltage drops in high-temperature proton exchange membrane fuel cells (HT-PEMFC)

Durability performance such as sintering and voltage drops of HT-PEMFC was theoretically evaluated under non-humid conditions at 150 °C, 170 °C and 190 °C. The quantum chemical molecular dynamics showed that the affinity of the platinum (Pt) electrocatalysts with carbon support decreased with increasing temperature. The degree of agglomeration of electrocatalysts over time simulated by three-dimensional kinetic Monte Carlo method was compared and quantitatively agreed with experimentally measured Transmission Electron Microscopy (TEM) results. Agglomeration of electrocatalysts due to the sintering caused losses of electrochemically active surface area, and found to be occurred more severe as temperature increased. Decreased rate of the proton conductivity due to the evaporation of phosphoric acid affected voltage drops as temperature increased. A theoretical breakdown of the voltage drops indicated that the voltage drops that occurred during the first several hundreds of hours and those occurring for the latter stage were due to different effects.     

Efficient Evaluation of System Reliability by Monte Carlo Method

This paper presents a new Monte Carlo method to estimate the reliability of a large complex system represented by a reliability block diagram or by a fault tree. Two binary functions are introduced; one dominates the system structure function and the other is dominated by the structure function. These functions can be constructed easily by using part of path sets and cut sets of the system. Through the use of these binary functions, two variance-reducing techniques (control variate and importance sampling) are applied to the Monte Carlo evaluation of the system reliability. We prove that the new Monte Carlo method gives a reliability estimate with a smaller variance than that of the crude Monte Carlo method.     

Nature of juvenile polyps in the large intestine

Forty-five juvenile polyps were found among approximately 390 mucosal polyps of the large intestine. Various degrees of epithelial pseudostratification were found among juvenile polyps and the larger-sized polyps of both juvenile type and adult one tended to have a more advanced degree of epithelial pseudostratification. The glands of both juvenile polyps and adult ones revealed a closely resembled or almost identical pattern of size-distribution-pattern of the glandular size in both normal mucosae and hyperplastic mucosae of long-standing ulcerative colitis. Transition of juvenile polyps into adult ones was suggested by the cases with increase in numbers of glands and their orifices to the surface of the polyp and there were some polyps showing an intermediate form between juvenile polyps and adult ones. On the basis of histologic characteristics and age incidence of the patients, it may be said that a juvenile polyp is an immature variant of an adult polyp.     

Activities of oxygen in liquid Bi-Pb and Bi-Sb alloys

The activity coefficient of oxygen, γ_o, in liquid Bi-Pb and Bi-Sb alloys at 1073 K has been measured over the entire composition range utilizing a modified coulometric titration method with the electrochemical cell: O in liquid Bi-Pb or Bi-Sb alloys/ZrO₂(+CaO)/Air, Pt. The measured In y0 values for both systems, plotted in terms of alloy composition, lie on upwardly concave curves. This behavior is significantly different from what is predicted by the quasi-chemical equations. The models of Wagner and of Blanderet al., which involve one adjustable parameter,h, give a satisfactory representation of the data. YOSHIKAZU KUROSE, formerly a Graduate Student, Osaka University, Osaka, 565, Japan     

The diffusivity of oxygen in liquid copper-lead alloys

The oxygen diffusivity in liquid copper-lead alloys at 1403 K (1130‡C) was measured us-ing the electrochemical cell: Ni-NiOJZrO₂(+CaO)/O in liquid Cu-Pb alloy(I)/ZrO₂(+CaO)/O in liquid Cu-Pb alloy(II). Oxygen in liquid Cu-Pb alloy(I) was transferred to the right by applying a preselected voltage between the two liquid Cu-Pb alloys. The oxygen diffusivity in liquid Cu-Pb alloy(I) was calculated from the emf change with time between the Ni-NiO and liquid Cu-Pb alloy (I) electrodes. The results were: D_o (in pure Cu) = 8.14 (^+0.70 _-0.43) × 10⁵ cm²/s, D_o (in Cu-25 at. pct Pb) = 11.4(^+0.4 _-0.6) × 10^-5 cm²/s, D_o (in Cu-50 at. pct Pb) = 12.9(^+1.9 _-1.5) × 10^-5 cm²/s, D_o (in Cu-75 at. pct Pb) = 11.0(^+2.4 _-1.2) x 10^-5 cm²/s, D_o (in pure Pb) = 26.3(^+4.8 _-3.7) × 10^-5 cm²/s. It was found that the oxygen diffusivity in liquid copper-lead alloys did not change dras-tically over the entire composition range, in contrast with that reported by other investi-gators for liquid copper-nickel alloys. The oxygen diffusivity in pure liquid lead agreed with the results of our previous work using an FeO-Fe₃O₄ mixture as a sink for oxygen.