Analysis of performance for centrifugal steam compressor

In this study, mean streamline and Computational fluid dynamics (CFD) analyses were performed to investigate the performance of a small centrifugal steam compressor using a latent heat recovery technology. The results from both analysis methods showed good agreement. The compression ratio and efficiency of steam were found to be related with those of air by comparing the compression performances of both gases. Thus, the compression performance of steam could be predicted by the compression performance of air using the developed dimensionless parameters.     

Supersonic turbine stator design using dense gas with numerical method

In recent years, interest in renewable energy as a substitute for power generation using coal has increased. As a next-generation power system, the Organic Rankine cycle (ORC) system, which requires a multi-stage turbine or a supersonic turbine to generate a high power, has been shown to have high potential for such uses. In this paper, a dense gas is chosen as a working fluid and a supersonic nozzle is designed for a supersonic turbine with advantages in terms of cost, power density and layout. Two stators are designed using the Method of characteristics (MOC) for air and dense gas. To validate the numerical model, the nozzle designed for the air is compared to that of a PIV experiment from the open literature, and the results indicate a reasonable agreement. The nozzle for the dense gas is different as that needed for air. Therefore, the modified MOC is applied based on a polytropic assumption. In conclusion, an estimation of the performance is implemented with loss coefficients for a different number of blades. The number of blades is shown to be proportional to the loss coefficient. For example, the case with the biggest numbers of blades is affected the most by the shock effect that occurs at the trailing edge.

     

Multi-walled carbon nanotube-reinforced copper nanocomposite coating fabricated by low-pressure cold spray process

Multi-walled carbon nanotube (MWCNT)-reinforced copper (Cu) nanocomposite coatings were successfully deposited on aluminum (Al) substrate by a cold spraying process at a low pressure. The microstructure and the Raman spectrum of the low-pressure-cold-sprayed MWCNT–Cu nanocomposite coating showed that the MWCNTs maintained their tube structure in the Cu matrix, even though structural damage to the MWCNTs increased slightly. MWCNT–Cu nanocomposite-coated Al exhibits higher thermal diffusivity than pure-Cu-coated Al with a comparable hardness. The higher thermal diffusivity of the MWCNT–Cu coating could be explained by the dispersion of MWCNTs within the clean and closed CNT/Cu interfaces, which were achieved with the aid of compressive stress during the cold spraying.     

Hydrothermal preparation of BaTiO3 thin films

In preparing BaTiO₃ thin films under hydrothermal conditions, the effects of concentrations of nutrient and mineralizer, and reaction time on crystallinity, grain size, surface roughness, and film thickness were investigated. Experiments were performed in the ranges of 0.1-1.5M BaCl₂ · 2H₂O or Ba(OH)₂ · 8H₂O and 0-1.5 M KOH with varying reaction time from 0.16 to 8 hours at 140 °C. Bimodal dispersion of crystalline grains on the surface of BaTiO₃ thin films was predicted through nucleation and crystal growth reaction. As the concentrations of nutrient and/or mineralizer increased, grain size of the thin film became smaller, but more uniform and compact. When 0.4 M Ba(OH)₂ · 8H₂O was used with 1.0 M KOH, a reaction time longer than 4 hours was required in order to fabricate BaTiO₃ thin films.     

Pervaporation behavior of asymmetric sulfonated polysulfones and sulfonated poly(ether sulfone) membranes

The sulfonation of polymers and the pervaporation behavior of asymmetric polymeric membranes are described in this study. We confirmed that the sulfonic acid group was successively introduced into the polymer chain by FTIR and ¹H‐NMR characterization. The phase diagram indicated that the modified polymer could have water tolerance, implying that the polymer–solvent miscibility was lower. The hyperthin skin layer, suitable for pervaporation, depended on the NMP–DGDE composition, which was important for the fabrication of an asymmetric membrane with high water permeance. The asymmetric membrane exhibited water selectivities equal to or slightly lower than those determined for the dense film. The hyperthin skin layer, which had hardly any defects, was possibly formed by the phase‐inversion method. It is obvious that these membranes can be used for the industrial pervaporation process. The permeability and the selectivity of the water–butanol mixture for the asymmetric membranes at 50°C were measured. The permeation rates for water–butanol in the asymmetric membrane were about 80 times greater than those of film, and the separation factor was slightly lower. The NMP–DGDE solvent system might be suitable for a high permeation rate. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 787–798, 2000     

Formation and corrosion of InP/In contacts in hydrochloric acid

Flatband potentials, charge carrier concentrations and their frequency dispersions of p-type and n-type InP in 1.0 M HCl were determined. The cathodic decomposition of InP in this acidic solution is compared with the deposition process of indium from 1.0 M-HCl containing 0.1 M InCl₃. The share of the involved reactions, hydrogen evolution, InP decomposition and indium deposition are investigated. The reaction rates are generally smaller on p-type InP and the reaction speed is much slower but the principal reactions are the same. The kinetics of the indium deposition and dissolution are studied in detail. These reactions are discussed in terms of the preparation of watersplitting photoelectrodes with modified surfaces.     

The selective sorption of D,L-amino acids by chemically modified chitosan gels and its application to liquid chromatography

The sorption of D ,L -amino acids, DNP-L -amino acids and dipeptides by N-octanoyl- and N-benzoyl-chitosan gels was investigated under various conditions. The results indicate that optical resolution of D ,L -amino acids by liquid column chromatography has been achieved, using the chemically modified chitosan gels as a stationary phase.     

Redox Properties and Catalytic Oxidation Activities of Polyatom-Substituted H n PW11M1O40 (M = V, Nb, Ta, and W) Keggin Heteropolyacid Catalysts

Redox properties and catalytic oxidation activities of polyatom-substituted H _n PW₁₁M₁O₄₀ (M = V, Nb, Ta, and W) Keggin heteropolyacids (HPAs) were examined. Reduction potentials and UV–visible absorption edge energies of H _n PW₁₁M₁O₄₀ (M = V, Nb, Ta, and W) HPA catalysts in solution were determined by an electrochemical method and UV–visible spectroscopy measurements, respectively. It was observed that reduction potentials of H _n PW₁₁M₁O₄₀ (M = V, Nb, Ta, and W) HPA catalysts increased and UV–visible absorption edge energies of the HPA catalysts decreased with decreasing electronegativity of substituted polyatom. It was also found that the lower absorption edge energy corresponded to the higher reduction potential of the HPA catalyst. Vapor-phase oxidation of benzyl alcohol was carried out as a model reaction to probe the redox properties of H _n PW₁₁M₁O₄₀ (M = V, Nb, Ta, and W) HPA catalysts. Yield for benzaldehyde increased with increasing reduction potential and with decreasing absorption edge energy of the HPA catalyst, and in turn, with decreasing electronegativity of substituted polyatom. Reduction potential of H _n PW₁₁M₁O₄₀ (M = V, Nb, Ta, and W) HPA catalysts measured by an electrochemical method and absorption edge energy of the HPA catalysts measured by UV–visible spectroscopy could be utilized as a probe of oxidation catalysis of the HPA catalysts.     

Dispersion Improvement of Platinum Catalysts Supported on Silica, Silica-Alumina and Alumina by Titania Incorporation and pH Adjustment

Platinum catalysts supported on silica, silica-alumina and alumina supports were prepared using four different cationic and anionic platinum precursors in order to examine the contribution of the precursors and supports to the platinum dispersion. The pH adjustment of the precursor suspension to obtain an opposing surface charge of the support to that on the platinum precursor ions considerably improved the platinum dispersion by strengthening their adsorption on the support. However, exceptional platinum dispersion was achieved, regardless of the precursor and support, by simultaneous pH adjustment and titania incorporation on the supports. The increase in the interaction between the platinum precursor and the titania-incorporated support raised the dispersion and stability of the platinum catalysts with high-loading, even after reduction at 400 °C. The physico-chemical states of platinum and titanium were investigated by XRD, TEM, XAFS spectroscopy and CO adsorption technique. The platinum catalysts supported on the titania-incorporated supports with pH adjustment exhibited highly dispersed platinum particles ranging in size from 1 to 3 nm. They also exhibited high catalytic activity in the oxidation of carbon monoxide because of its incorporated titania and partially oxidized, small platinum particles.     

Physical degradation of MEA in PEM fuel cell by on/off operation under nitrogen atmosphere

The durability of PEMFCs is one of the most important issues for application in automotive vehicles with a repeated start-up and shut-down system. The understanding of degradation phenomena such as causes, mechanisms and influence of working condition is essential to improving the performance and lifetime of PEMFC. We conducted on/off cyclic operation in a single cell configuration with ultra purity nitrogen gas to investigate the physical degradation of membrane electrode assembly (MEA). After on/off cycle operation for 100,000 cycles under different humid condition, the characteristics of the MEAs were examined by in situ and ex situ analyses techniques. The physical degradation of MEA by on/off cycling led to a change in the membrane-electrode interfacial structure, which is mainly attributed to the loss of cell performance.