Multi-fluid simulation of turbulent bubbly pipe flows

Radial distributions of void fraction α_G, bubble aspect ratio E, phasic velocities V_G and V_L and turbulent kinetic energy k in bubbly pipe flows are measured using an image processing method and a laser Doppler velocimetry. Multi-fluid simulations are conducted to examine applicability of state-of-the-art closure relations to the turbulent bubbly pipe flows. The experimental results indicate that aspect ratio of bubbles in the near wall region takes a higher value than that of free rising bubbles due to the presence of wall, and that the change in the aspect ratio induces decrease in relative velocity between bubbles and liquid in the near wall region. Drag coefficient C_D of a bubble in a bubbly pipe flow tends to increase with magnitude of shear flow, and the effect of shear flow on C_D is estimated by the correlation proposed by Legendre and Magnaudet (1998). Comparison between the simulated and the measured results indicate that the effects of bubble shape and shear flow on drag force acting on bubbles should be taken into account for accurate predictions of bubbly pipe flows. The turbulence models proposed by Lopez de Bertodano et al. (1994) and by Hosokawa and Tomiyama (2004a) give good predictions for turbulence modification caused by bubbles.     

Effect of Support Materials on the Selective Methanation of CO over Ru Catalysts

Selective methanation of CO in the reformate gas (CO/CO₂/H₂/H₂O = 0.175/17.9/70.9/11.1) proceeded over Ru catalysts supported on metal oxides and zeolites. CO was selectively methanated at wide temperature ranges (200–275 °C) over Ru/γ-Al₂O₃, Ru/TiO₂ Ru/H-Y and Ru/H-beta catalysts. Higher Ru contents in Ru/γ-Al₂O₃ improved the selective CO methanation rate.     

Robust and accurate prediction of thermal error of machining centers under operations with cutting fluid supply

A novel temperature measuring system named LATSIS was proposed to realize a robust and accurate prediction of the thermal deformation of machining centers, even under external disturbances such as cutting fluid supply. LATSIS enables a drastic increase in the number of sensors employed for measuring the temperature of the machine tool. Thus, the entire temperature distribution can be obtained by interpolating the measured temperature 3-dimensionally without calculating the heat conduction. A set of experiments was conducted in which the LATSIS was employed to predict the TCP error. A total of 284 sensors were placed on the machining center, and the TCP error was predicted based on the measured temperature for the situation with/without the cutting fluid supply. The results of the prediction showed good agreement with the measured TCP error even during the initial transient temperature change as well as in the cooling phase after the machine halt. The TCP error with the cutting fluid supply is accurately predicted. LATSIS was proven to be a robust and accurate method for predicting the thermal deformation of machine tools, and is a promising technology for future manufacturing systems.     

The micro-nanoformability of Pt-based metallic glass and the nanoforming of three-dimensional structures

Pt_48.75Pd_9.75Cu_19.5P₂₂ amorphous alloy exhibits obvious glass transition behavior at a temperature of T_g=502 K, which is below the crystallization temperature T_x=588 K, and develops a supercooled liquid state in a wide temperature range of ΔT_x (=T_x−T_g)=86 K. The present paper investigates the macroscopic and microscopic deformation behavior of the material and the possibility of micro-nano forming as a fabrication method and material for nano-devices. On a macroscopic scale, the material exhibits a Newtonian viscous flow in a supercooled liquid state. An index of the microformability is also evaluated by the geometrical transferability of a die shape to the material. For this study, we fabricated V-grooved micro dies of (100) Si by a silicon process. The V-groove dies are from 100 nm to 1 μm wide. The material exhibits superior formability on micrometer and nanometer scales and may possibly be applied to micro-nanomaterials for micro-nano devices.     

Pore Structure and Thermal Stability of Mesoporous Mullite Fibers Prepared by Crystallization and Selective Leaching of Al2O3-SiO2 Glass Fibers

Porous mullite fibers were prepared by crystallization and selective leaching of Al2O3-SiO2 glass fibers using buffered HF-NH4F(BHF) aqueous solutions. The optimum concentration of BHF solution for selective leaching of the fibers was 0.9 mass% HF and 17.0 mass% NH4F. By firing at 1000–1300°C, the glass fibers changed into composite texture of mullite and glassy phase. Since the pores in the fibers were formed by selective leaching of glassy phase among mullite grains, they were tunable by changing the firing conditions of fibers. Pore size of the samples changed from around 4 nm in the 1100°C fired sample to 16 and 40 nm in the 1200 and 1300°C fired samples, respectively. The highest specific surface area obtained was around 30 m2/g, when the fibers were heat treated at 1200°C for 24 h and leached for 20 h in 0.9 mass% HF-17.0 mass% NH4F solution. From the thermal stability tests of the porous mullite fibers, its specific surface area was found to be maintained up to 1200–1300°C.     

Vapor-phase kinetics and its contribution to global three-phase reaction rate in hydrogenation of 1-methylnaphthalene

It has been considered that the contribution of the vapor-phase reaction (VPR) to the global three-phase reaction rate may become much lower as the catalyst effectiveness factor approaches unity. In this study, the hydrogenation of 1-methylnaphthalene was performed as an example of slow reactions using a laboratory-scale trickle-bed reactor (TBR) at 583 K, 8.0 MPa. It was qualitatively confirmed that VPR contributed to the product yields in TBR even in this slow reaction system when the liquid velocity was low and the volatility of the liquid was high. Langmuir–Hinshelwood type kinetic equations were established for the vapor-phase reaction. The product yields in TBR neither be explained by liquid- vapor-phase kinetics without external effects, nor the conventional partial wetting model. Therefore, a partial wetting model considering the contribution of VPR was proposed where the catalyst bed composed of externally partial and internally complete wet particles, and completely dry particles was assumed. Using this model, the product yields in TBR were suitably explained.     

Nanoparticle formation in H2O/N2 and H2O/Ar mixtures under irradiation by 20 MeV protons and positive corona discharge

To investigate the contribution of ions to gas nucleation, we have performed experiments on the formation of water droplets in H₂O/N₂ and H₂O/Ar gas mixtures by irradiation with a 20 MeV proton beam and by positive corona discharge. The size of the formed nanoparticles was measured using a differential mobility analyzer equipped with a Faraday cup electrometer. Using the proton beam, droplets around 10 nm in diameter were observed for both positively and negatively charged particles, but none were found when the corona discharge was used. This implies the importance of the presence of both positive and negative ions for the formation of nanosize droplets, which attract each other by Coulomb interactions, enhancing the collision frequency and leading to the formation of the 10 nm droplets.     

Contact and interconnect formation on compound semiconductor devices by ionized-cluster beam deposition

A new deposition technology, namely the ionized-cluster beam deposition method, was applied to form contacts and interconnects on III–V compound semiconductor devices. Au alloy films deposited by this technology had strong enough adhesion to an insulator layer to be a satisfactory interconnection. A step approximately 8 μm high at an angle of 90° to the semiconductor was covered fully with an Au alloy film obtained by this method. Electrical ohmic contacts for p-type GaP and GaAs were successfully obtained at substrate temperatures of 400 °C and 300 °C respectively without any further annealing process; this resulted in better device characteristics because of the lower process temperatures and also made the device less expensive because of a reduction in fabrication time.