Numerical study of effect of oxygen fraction on local entropy generation in a methane-air burner

This study considers numerical simulation of the combustion of methane with air, including oxygen and nitrogen, in a burner and the numerical solution of local entropy generation rate due to high temperature and velocity gradients in the combustion chamber. The effects of equivalence ratio (Φ) and oxygen percentage (γ ) on combustion and entropy generation rates are investigated for different Φ (from 0.5 to 1.0) andγ values (from 10 to 30%). Combustion is simulated for the fuel mass flow rate resulting in the same heat transfer rate (Q)y to the combustion chamber in each case. Numerical calculation of combustion is performed individually for all cases with the use of the Fluent CFD code. Furthermore, a computer program has been developed to calculate the volumetric entropy generation rate and the other thermodynamic parameters numerically by using the results of the calculations performed with the FLUENT code. The predictions show that the increase of Φ (or the decrease of λ) significantly reduces the reaction rate levels. Average temperature in the combustion chamber increases by about 70 and 35% with increase ofγ (from 10 to 30%) and Φ (from 0.5 to 1.0) respectively. With increase ofγ from 10 to 30%, volumetric local entropy generation rate decreases by about 9 and 4% for Φ = 0.5 and 1.0 respectively, while total entropy generation rate decreases exponentially and the merit numbers increase. The ratio of the rates useful energy transfer to irreversibility therefore improves as the oxygen percentage increases     

From Bifunctional Site to Metal–Proton Adduct Site in Alkane Reforming Reactions on Sulphated-Zirconia-Supported Pt or Pd or Ir Catalysts

Isomerization reactions of n-heptane, n-octane and n-nonane are studied on sulphated-zirconia-supported 0.2 wt% Pt, Pd or Ir catalysts. Evolutions of isomer selectivity versus total conversion and reaction temperatures are analysed. When total conversion (_T) is increased, isomer selectivity (%S _isom) is decreased and the slope of the curve %S _isom=f(_T) is more pronounced when the carbon number in the alkane is more important. At isoconversion, around 20%, below 473 K, cracking is favoured over isomerization reaction, and above 473 K it is the reverse. Moreover, with n-heptane, when the catalytic reaction occurred at 423 K and at low conversion, _T20%, we observed a large decrease in the isomer selectivity percentages on Pd/SZ and Ir/SZ compared to Pt/SZ. What is remarkable is that, at this low temperature, both metals are inactive in the carbon–carbon bond rupture. To explain these results the following points are raised: (i) an associative mechanism is proposed for the adsorption step of the alkane involving an agostic intermediate species where the carbon–hydrogen bonds act as ligands to the transition metal centres forming covalent C–HM systems, and (ii) a metal–proton adduct site, which gathers metallic and acidic sites is suggested. This approach seems to better explain our results than the traditional bifunctional mechanism.     

A supramolecular sensing platform for phosphate anions and an anthrax biomarker in a microfluidic device

A supramolecular platform based on self-assembled monolayers (SAMs) has been implemented in a microfluidic device. The system has been applied for the sensing of two different analyte types: biologically relevant phosphate anions and aromatic carboxylic acids, which are important for anthrax detection. A Eu(III)-EDTA complex was bound to β-cyclodextrin monolayers via orthogonal supramolecular host-guest interactions. The self-assembly of the Eu(III)-EDTA conjugate and naphthalene β-diketone as an antenna resulted in the formation of a highly luminescent lanthanide complex on the microchannel surface. Detection of different phosphate anions and aromatic carboxylic acids was demonstrated by monitoring the decrease in red emission following displacement of the antenna by the analyte. Among these analytes, adenosine triphosphate (ATP) and pyrophosphate, as well as dipicolinic acid (DPA) which is a biomarker for anthrax, showed a strong response. Parallel fabrication of five sensing SAMs in a single multichannel chip was performed, as a first demonstration of phosphate and carboxylic acid screening in a multiplexed format that allows a general detection platform for both analyte systems in a single test run with μM and nM detection sensitivity for ATP and DPA, respectively.     

Efficiency of hydrogen production systems using alternative nuclear energy technologies

Nuclear energy can be used as the primary energy source in centralized hydrogen production through high-temperature thermochemical processes, water electrolysis, or high-temperature steam electrolysis. Energy efficiency is important in providing hydrogen economically and in a climate friendly manner. High operating temperatures are needed for more efficient thermochemical and electrochemical hydrogen production using nuclear energy. Therefore, high-temperature reactors, such as the gas-cooled, molten-salt-cooled and liquid-metal-cooled reactor technologies, are the candidates for use in hydrogen production. Several candidate technologies that span the range from well developed to conceptual are compared in our analysis. Among these alternatives, high-temperature steam electrolysis (HTSE) coupled to an advanced gas reactor cooled by supercritical CO₂ (S-CO₂) and equipped with a supercritical CO₂ power conversion cycle has the potential to provide higher energy efficiency at a lower temperature range than the other alternatives.     

Electrical Characteristics of Al/Poly(methyl methacrylate)/p-Si Schottky Device

Al/Poly(methyl methacrylate)(PMMA)/p-Si organic Schottky devices were fabricated on a p-Si semiconductor wafer by spin coating of PMMA solution. The capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics of Al/PMMA/p-Si structures have been investigated in the frequency range of 1 kHz–10 MHz at room temperature. The diode parameters such as ideality factor, series resistance and barrier height were calculated from the forward bias current–voltage (I–V) characteristics. In order to explain the electrical characteristics of metal–polymer–semiconductor (MPS) with a PMMA interface, the investigation of interface states density and series resistance from C–V and G–V characteristics in the MPS structures with thin interfacial insulator layer have been reported. The measurements of capacitance (C) and conductance (G) were found to be strongly dependent on bias voltage and frequency for Al/PMMA/p-Si structures. The values of interface state density (D _it) were calculated. These values of D _it and series resistance (R _s) were responsible for the non-ideal behavior of I–V and C–V characteristics.     

The changes in the Mechanic Properties of a direct tableting agent Microcrystalline Cellulose by Precompression

In the manufacturing of tablets, direct tableting agents are not only used in direct compression, but are also used in wet granulation and slugging methods. These agents are effective only if their particle size and form is appropriate. However, the precompression, milling and grinding which are applied in the slugging method changes the particular properties of these agents.

In this study, microcrystalline cellulose tablets were prepared both by direct compression and slugging. The consolidation, compressibility and flow properties of the two mixed powders were compared. Finally, it was observed that the compressibility of the mixed powder was influenced negatively by the slugging method.     

Review on Advanced EB-PVD Ceramic Topcoats for TBC Applications

Development of electron beam physical vapor deposited (EB-PVD) thermal barrier coatings (TBC) aims at low conductivity, increased temperature capability, and longer life. Considerable progress has been achieved by comprehensive understanding of the evolvement of the porous microstructure in columnar ceramic topcoats and its application to tailoring optimized micro-structures. New ceramic compositions such as alternative stabilizers in zirconia, hafnia modified coatings, and pyrochlores are addressed. They have demonstrated their potential for future TBC applications. New results of both microstructure and chemistry are presented together with a summary of recent research results.     

An investigation of mechanical and metallurgical properties of explosive welded aluminum-dual phase steel

The aim of this paper is investigation of microstructure and property relationship in aluminum-HSLA steel and aluminum-dual phase steel bimetals fabricated by explosive welding technique. Dual phase steel was produced by intercritical annealing and water quenching from 1.45Mn-0.2Si-0.186C HSLA steel. Hardness, tensile shear strength, tensile strength, toughness and microstructure of explosively welded aluminum-HSLA steel and aluminum-dual phase steel were evaluated. Both bimetals have a straight bonding interface. It was also seen that plastic deformation of dual phase steel was higher than HSLA steel near interfaces of bimetals. The hardness was increased near the bond interface of bimetals. Tensile and tensile shear strength tests showed that aluminum-dual phase steel is superior than aluminum-HSLA steel. Also, impact toughness of aluminum-dual phase steel was found significantly higher than that of aluminum-HSLA steel.     

Modeling of a blending and marine transportation planning problem with fuzzy mixed-integer programming

Transportation management is an area that remains critical to overall logistics and supply chain success. The problem of multi-commodity, multi-period blending and marine transportation planning in a wheat supply chain is addressed in this paper. In real world problems, practical situations are often not well-defined and thus cannot be described precisely. Therefore fuzzy mathematical programming becomes a valuable extension of traditional crisp optimization models. This research resolves the blending and marine transportation planning problem using fuzzy mixed-integer programming (FMIP) method. Two types of fuzzy mathematical programming models are used. A real-life example is used to illustrate the potential savings which can be attained by using fuzzy models. Results obtained in this study clearly demonstrate that FMIP provides a better and more flexible way of representing the problem.