Aerodynamic Performance and Noise Characteristics of a Centrifugal Compressor with Modified Vaned Diffusers

Improvement of aerodynamic performance and reduction of interaction tone noise of a centrifugal compressorwith vaned diffusers are discussed by experiments and visualization techniques using a colored oil-film method.The focus of the research is concentrated on the leading edge shape of diffuser vanes that are deeply related to thegeneration mechanism of the interaction tone noise.The compressor-radiated noise can be reduced by more thanten decibels by using modified diffuser vanes which have 3-D tapered shapes on both pressure and suction sur-faces of the leading edge.Furthermore,by adopting the proposed modified diffuser vanes,the secondary flowwhich is considered to be an obstruction of diffuser pressure recovery can be suppressed,and also the pressuredecrease observed in the throat part of the diffuser flow passage is reducible.Thus,the proposed diffuser vanesshow a favorable result for both noise and the aerodynamic performance of the centrifugal compressor,and offera few basic guidelines for the diffuser vane design.     

Anaerobic treatment performance and microbial population of thermophilic upflow anaerobic filter reactor treating awamori distillery wastewater

Distillery wastewater from awamori making was anaerobically treated for one year using thermophilic upflow anaerobic filter (UAF) reactors packed with pyridinium group-containing nonwoven fabric material. The microbial structure and spatial distribution of microorganisms on the support material were characterized using molecular biological methods. The reactor steadily achieved a high TOC loading rate of 18 g/l/d with approximately 80% TOC removal efficiency when non-diluted wastewater was fed. The maximum TOC loading rate increased to 36 g/l/d when treating thrice-diluted wastewater. However, the TOC removal efficiency and gas evolution rate decreased compared with that when non-diluted wastewater was used. Methanogens closely related to Methanosarcina thermophila and Methanoculleus bourgensis and bacteria in the phyla Firmicutes and Bacteroidetes were predominant methanogens and bacteria in the thermophilic UFA reactor, as indicated by 16S rRNA gene clone analysis. Fluorescence in situ hybridization (FISH) results showed that a large quantity of bacterial cells adhered throughout the whole support, and Methanosarcina-like methanogens existed mainly in the relative outside region while Methanoculleus cells were located in the relative inner part of the support. The support material used proved to be an excellent carrier for microorganisms, and a UAF reactor using this kind of support can be used for high-rate treatment of awamori/shochu distillery wastewater.     

A real-time polishing force control system for ultraprecision finishing of micro-optics

Polishing force condition plays a key role in the ultraprecision finishing of micro-optics because it strongly affects the polishing performance. In this paper, a novel polishing force control system is developed to improve the polishing stability. It is proposed for the first time to precisely control polishing force in real-time and has a simple mechanism which mainly composes of a load cell, a piezo stage and a linear stage. The load cell is used to measure the polishing force, whereas the piezo-stage is applied to adjust the force with nano/micro positioning change. The linear stage driven by a stepper motor is employed to prevent force change beyond the travel range of piezo stage which leads to the system out of control. A PID controller is adopted to calculate the command voltage for driving the piezo-stage based on the measured force. The system enables polishing force to be controlled within a range of 0–200 mN with a resolution of 0.1 mN. Some fundamental experiments are conducted to evaluate the performance of newly developed system. The results indicate that the proposed polishing force control system enables a stable polishing, and the polishing force conditions which generate suitable material removal function are acquired.     

Electrochemical reduction of graphene oxide in organic solvents

Graphene oxide (GO) cast on conductive substrates was electrochemically reduced in some organic solvents. The amount of electricity required for the almost complete reduction of GO was 2.0 C for 1 mg GO, corresponding to attaching of a one-electron reducible species to each benzene ring in graphene. The electrochemically reduced GO film gave an electrical conductivity of about 3 S cm⁻¹ and exhibited a relatively high specific capacitance of 147.2 F g⁻¹ in propylene carbonate. The electrochemical reduction of GO was feasible on Al foils as well.     

Crystallization of polypropylene near the surface in injection‐molded plaques: A comparison of morphology and a numerical analysis

Skin morphology formation on injection‐molded isotactic polypropylene (PP) was investigated using micro‐beam synchrotron wide‐angle X‐ray diffraction and numerical simulation. The 1–20 μm depth range was characterized with an X‐ray beam of 0.273 μm χ 0.389 μm in size. From an evaluation of doping nucleating agents (NA) in PP, the NAs did not work at a depth of 1 μm. α‐specified NA affected crystallization within a 5‐μm depth. β‐specified PP showed α‐form crystallinity at the 5–20 μm depth. The mesomorphic crystal near the surface showed extremely high orientation. From viscoelastic flow simulation, PP molecules near the surface were oriented in the flow direction by extensional flow in the flow front, but freezing occurred faster than flow‐induced crystallization. It was estimated that the delay of crystallization occurred during the transient temperature. The deformation rate did not cause a difference in crystal morphology near the surface, but the cooling rate did. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.     

Relating scratch resistance to injection molding‐induced morphology of polypropylene

The relationship between the scratch resistance and the injection molding‐induced morphology of polypropylene (PP) was investigated. The crystal structure near the surface was controlled by the mold temperature and the doping of a nucleating agent (NA). Although α‐ and β‐NA were used to improve the scratch resistance of PP that was molded at a mold temperature of 40°C, both of the NAs only slightly affected the scratch resistance due to low crystallinity at the surface. When the mold temperature was increased, the skin layer became thin and a β‐form crystal formed. Plastic deformation under the scratch was limited in the frozen layer. Consequently, the thickness of the frozen layer (which had low crystallinity) had the predominant effect on the scratch resistance in comparison to the polymorphism differences. The crystal morphology was analyzed with synchrotron micro‐beam wide angle X‐ray diffraction and Fourier transform infrared spectroscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis,thermal, and photo alignment behavior of polyethylene imines having nitro substituent azobenzene side chain group

Polyethylene imines having nitro substituent azobenzene side chain group with different methylene spacer groups (PEImN) were successfully synthesized and characterized by differential scanning calorimetry, polarized optical microscopic, and X‐ray diffraction analysis. All synthesized polyethylene imines showed liquid crystalline properties and the glass transition temperature (Tg) of PEImN decreased as the number of methylene spacers increased. Melting temperatures (Tm) of synthesized PEImN showed an odd‐even effect. Photochemical, thermo‐optical, as well as photo alignment behavior of PEImN were investigated and out‐of‐plane orientational behavior of polymeric films was dependent on number of methylene spacers and polyethylene imines having higher number of methylene spacers (six or more) showed high order parameter values that revealed the well pronounced tendency for the development of out‐of‐plane order from random state on annealing. And the molecular orientation of PEImN between random and out‐of‐plane structures has been achieved by the combination of thermal and photochemical processes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Oxidation behavior of ZrB2-MoSi2-SiC composites in air at 1500 °C

We investigated the oxidation behavior and the effect of the amount of SiC added on oxidation resistance in both hot-pressed ZrB₂-MoSi₂-SiC composites, 55ZrB₂-40MoSi₂-5SiC and 40ZrB₂-40MoSi₂-20SiC (vol.%), exposed to dry air at 1500 °C for up to 10 h. Quantitative electron microprobe analysis characterizations of the chemical compounds of post-oxidized composites were carried out. Parabolic oxidation behavior was observed for both composites. The addition of SiC improved the oxidation resistance of ZrB₂-MoSi₂-SiC composites, and the improvement enhanced with amount of SiC added. The microstructure of the post-oxidized composites consisted of two characteristic regions: oxidized reactive region and unreactive bulk material region. The oxidized reactive region divided into an outermost dense silica-rich scale layer and oxidized reactive mixture layer. The improvement of oxidation resistance with SiC addition is associated with the presence of a thicker dense outermost scale layer which inhibited inward diffusion of oxygen through it.     

Static and seismic studies on steel/concrete hybrid towers for multi-span cable-stayed bridges

A new type of hybrid high tower is proposed and applied to a multi-span cable-stayed bridge. This is basically a sandwich type structure and consists of a steel double box section filled with concrete. The filled concrete increases its strength due to the confined effect and the steel plates increase the resistance against local buckling because the deformation is restricted by the filled concrete. Therefore, this hybrid tower is expected to have high bending and compressive strength, and also a good ductile property. First, static analysis is conducted for different live load intensity and distribution because the multi-span cable-stayed bridge is a new structure and its static behavior is not fully understood. The live loads distributed in alternate spans give larger bending moment of the towers than the live loads distributed in full spans. Towers with three different heights are also studied, showing that the higher tower produces smaller displacements and bending moments. Safety of the tower is checked by the limit states design method. Serviceability is not a major problem for the hybrid tower. Second, seismic analysis is carried out for a multi-span cable-stayed bridge subjected to the medium and ultra-strong seismic waves specified in Japanese Seismic Code for Highway Bridges. Three support conditions of the girder at the tower cross beams are compared: movable, connection with linear springs and bi-linear springs. Bi-linear springs are very effective in reducing the dynamic displacements and bending moments of the towers. Restorability of the composite tower is checked when an ultra-strong seismic wave hits the model bridge. This study shows that a new steel/concrete hybrid tower is feasible for multi-span cable-stayed bridges and most effective for seismic forces when the girder is connected with bi-linear springs.     

O2-releasing reactivity of ceria-based reactive ceramics on irradiation of artificial concentrated solar beam for solar hydrogen production

In the present paper, different types of metal doped ceria CeO₂–MO_x (M = Sc, Y, Dy, Zr and Hf) with fluorite structure have been prepared with a complex polymerization method. The O₂-releasing potential of prepared samples was evaluated at 1500 °C for a two-step water splitting process. The partially oxygen defected CeO₂–MO_1.5 (M = Sc³⁺, Y³⁺ or Dy³⁺) mixed oxide exhibited an enhancement of the O₂ evolution on CeO₂–ScO_1.5 owing to the crystal-chemical effect that cation with smaller ionic radius (Sc³⁺) compensates the volume expansion of crystal lattice resulted in the reduction of Ce⁴⁺ with smaller ionic radius into Ce³⁺ with larger ionic radius. The CeO₂–MO₂ (M = Zr⁴⁺ and Hf⁴⁺) produced larger amount of O₂ than that for CeO₂–MO_1.5 mixed oxides, since CeO₂–MO₂ has no oxygen vacancy initially. While the ionic radii of Zr⁴⁺ and Hf⁴⁺ are almost equal, the higher O₂-releasing reactivity of Ce_0.9Hf_0.1O₂ than that of Ce_0.9Zr_0.1O₂ is explained in terms of ionicity of M–O bond. Also, the weight losses of CeO₂, Ce_0.9Zr_0.1O₂ and Ce_0.9Hf_0.1O₂ in the mitigation process from high PO₂${\text{P}}_{{\text{O}}_2}$ (O₂ gas stream) to low PO₂${\text{P}}_{{\text{O}}_2}$ (Ar gas stream) atmosphere were determined. The quasi activation energies in the initial period of the O₂-release for CeO₂, Ce_0.9Zr_0.1O₂ and Ce_0.9Hf_0.1O₂ were evaluated 105, 84.2 and 75.0 kJ/mol, respectively. The O₂-releasing reactivity is considered from the standpoint of an activation energy.