Methanol electro-oxidation by a ternary Pt–Ru–Cu catalyst identified by a combinatorial approach

Composition optimization of the ternary Pt–Ru–Cu system for the methanol electro-oxidation reaction (MOR) was performed by combinatorial synthesis and high-throughput screening methods. A thin film library of the Pt–Ru–Cu system was prepared by a sputtering system to generate 63 different compositions. The compositions were characterized in parallel by a multichannel multielectrode analyzer. The highest MOR activity was observed for the Pt₆₆Ru₁₇Cu₁₇ composition. The Pt₆₆Ru₁₇Cu₁₇/C composition was synthesized and characterized as a powder catalyst to verify the performance of this new composition. During cyclic voltammetry tests, the Pt₆₆Ru₁₇Cu₁₇/C catalyst showed less dissolution and irreversible oxidation of Ru than a Pt₅₀Ru₅₀/C catalyst, with increasing number of cycles. In MOR activity measurement experiments, the Pt₆₆Ru₁₇Cu₁₇/C catalyst exhibited 26 and 86% higher activities in cyclic and chronoamperometric tests, respectively, than those of the Pt₅₀Ru₅₀/C catalyst.     

CO2 payback–time assessment of a regional-scale heating and cooling system using a ground source heat–pump in a high energy–consumption area in Tokyo

We present an assessment of installing a regional heating and cooling system in the Nishi(West)-Shinjuku area of Tokyo, Japan. In this assessment, we estimate the CO₂ payback–time, when air source heat–pumps (ASHP) are replaced with a ground–source heat–pump (GSHP) system. We calculate CO₂ emissions from transportation of the cooling tower, materials for the underground heat exchanger, and the digging loads and transportation loads incurred when the GSHP system is installed to replace the air source cooling system. The total CO₂ emission from the installation of the GSHP system was estimated to be 67,701t-CO₂, with 87% of the CO₂ emissions resulting from the digging process. CO₂ emissions from the operation of the GSHP system were estimated from the total energy-efficiency of the system and the heating and cooling demand in Nishi-Shinjuku area. Using the GSHP system, 33,935t-CO₂ would be emitted per year. We estimate that using the GSHP system would result in a reduction of 54% of the CO₂ emissions, or 39,519t-CO₂ per year. From these results, the CO₂ payback–time for replacing the conventional ASHP in the 1 km² studied region with the GSHP system is assessed to be 1.7 years.     

An exergy–cost–energy–mass analysis of a hybrid copper–chlorine thermochemical cycle for hydrogen production

An exergoeconomic assessment using exergy–cost–energy–mass (EXCEM) analysis is reported of a copper–chlorine (Cu–Cl) thermochemical water splitting cycle for hydrogen production. The quantitative relation is identified between capital costs and thermodynamic losses for devices in the cycle. A correlation detected in previous assessments, suggesting that devices in energy systems are configured so as to achieve an overall optimal design by appropriately balancing thermodynamic (exergy-based) and economic characteristics of the overall system and its components, is observed to apply for the Cu–Cl cycle. Exergetic cost allocations and various exergoeconomic performance parameters are determined for the overall cycle and its components. The results are expected to assist ongoing efforts to increase the economic viability and to reduce product costs of potential commercial versions of this process. The impacts of these results are anticipated to be significant since thermochemical water splitting with a copper–chlorine cycle is a promising process that could be linked with nuclear reactors to produce hydrogen with no greenhouse gases emissions, and thereby help mitigate numerous energy and environment concerns.     

Study of a SOFC with a bimetallic Cu–Co–ceria anode directly fuelled with simulated biogas mixtures

The present work is focused in the study of the bimetallic Cu–Co formulation combined with CeO₂ as SOFC anode, at 750 °C, direct feed of methane and two different fuel mixtures that simulate biogas. Additionally, the sulphur tolerance of new anode material has been evaluated. Its single cell evaluation, based on a samaria doped ceria (SDC) solid electrolyte and a LSM perovskite cathode, together with the electrochemical characterisation and catalytic activity tests, have allowed to demonstrate the ability of this material to operate directly with simulated biogas mixtures without loss of single cell performance due to the formation of carbon deposits or sulphur anode poisoning. The activity of this material for the exothermic oxidation of methane reduces the energy requirement of the endothermic internal methane reforming process. The cobalt doping of basic copper–ceria formulation enhanced sulphur and carbon coking tolerance of the SOFC anode material.     

Heat transfer in a reaction–diffusion system with a moving heat source

A general formulation is presented for a moving boundary problem in which heat is generated at the boundary due to an exothermic reaction involving a species which diffuses into a dispersed phase from an external medium of finite volume. The speed of the moving boundary is prescribed based on the solution of the mass diffusion problem and an analysis is presented of the thermal dynamics of the system. The set of equations describing heat transport leads to a Green’s function type problem with time dependent boundary conditions and the Galerkin finite element method is employed to develop a numerical solution. Transformations are introduced to freeze the moving boundary and partition the domain for ease of computation, and an iterative scheme is defined to satisfy the heat flux jump boundary condition and match the temperature field across the moving boundary. The numerical results are used to set the limits of applicability of an analytical perturbation solution. Essential aspects of thermal dynamics in the system are described and parametric regions resulting in a local temperature hot spot are delineated. Computed contour plots describing thermal evolution are presented for different combinations of parameter values. These may be of utility in the prediction of thermal development, for control and avoidance of hot spot formation, and in physical parameter estimation.     

Online humidification diagnosis of a PEMFC using a static DC–DC converter

This paper deals with the online checking of the humidification of a Proton Exchange Membrane Fuel Cell (PEMFC). Indeed, drying or flooding can decrease the performance of the PEMFC and even lead to its destruction. An online humidification diagnosis can allow a real-time control. A good indicator of the membrane humidification state is its internal resistance. As known, the membrane ionic conductivity increases with the membrane water content. This resistance can be calculated at high frequency by dividing the voltage variation by the current variation. The proposed scheme makes use of measurements of current and voltage ripples coming from the association of a static DC–DC converter and the fuel cell. The experiment thus consists in computing the internal resistance in wet and dry conditions.     

Synthesis and hydrogen storage characteristics of Mg–B–H compounds by a gas–solid reaction

Magnesium borohydride [Mg(BH₄)₂] is an attractive complex hydride for hydrogen storage. In this study, attempts to synthesize Mg(BH₄)₂ were carried out by a solid–gas reaction through MgH₂ and B₂H₆ in the absence of a liquid medium. The source of B₂H₆ was obtained by heating a mixture of NaBH₄ and ZnCl₂. The profile of pressure versus temperature indicated that the absorption kinetics of B₂H₆ by MgH₂ were slow. Structural analysis confirmed the formation of Mg–B–H compounds. The reaction products presented two-step hydrogen release during heating. A small amount of hydrogen could be released from the as-synthesized Mg–B–H compounds at a low temperature of 215 °C. The slow reaction kinetics were significantly affected by the surface conditions of the MgH₂ powders.     

Picard–Fuchs Equations and Gauss–Manin Systems with a View Towards the Riemann–Hilbert Problem

We study Abelian integrals associated with a tame polynomial function and their Picard–Fuchs equations using the theory of algebraic Gauss–Manin systems. Especially, we look for a basis of the Petrov module, in which the Picard–Fuchs equations become as simple as possible. As an application, we discuss the related Riemann–Hilbert problem and prove that it has a positive answer under some conditions. In this case, we compute the Jordan normal form of the residue matrices of the corresponding Fuchsian system in terms of local data. 2000 Mathematics Subject Classification. 32S40, 34C20.     

Optimal sizing of a solar–biogas-based cooking system for a cluster of villages

Energy supplies particularly in remote and far-flung rural areas are in pathetic situation. Leave aside other needs, most of the rural communities still use wood as a source of energy for cooking. Burning of wood is not only an inefficient method, but also hazardousness for the person working on the stove. People have been working for cleaner and efficient means of cooking for decades. Solar cooker- and biogas-based cook stoves are two of the successfully implemented technologies in this area. Although solar cooker requires no maintenance, the initial investment is quite high for a cluster of villages. In addition to this, the intermittency involved in solar energy makes this an unreliable source.

In this paper, a cluster of villages of Narendra Nagar block of Tehri Garhwal district of Uttarakhand, India, has been studied in terms of their thermal requirements. The potential of solar energy and biomass energy has been estimated. An integrated solar–biogas system has been proposed to satisfy this cooking demand. To obtain the optimal sizes of solar cooker and biogas generator, MATLAB codes have been developed. It was found that this system is more economical and much reliable than the other two cases.     

Longevity test for a Water–Gas Shift catalyst

Catalyst poisoning is one of the most significant problems associated with the commercial application of water gas shift catalysts. Conventional site blocking poisoning with sulphur compounds, and particularly by H₂S, is common. This work reports the effect of H₂S exposure on a Pt-based Water–Gas Shift catalyst. A 100 h continuous experiment was made to study the catalyst viability in the presence of 1 ppm H₂S. As well as different experimental conditions, temperature, gas hourly space velocity, steam carbon ratio and a concentration of 300 ppm H₂S. Gas chromatography (GC) was used in this study to analyse the outlet gas composition through time, and thereby the catalyst performance.     

Study on a new ejection–absorption heat transformer

Based on the performance analysis of the single stage, the two-stage and the double absorption heat transformer, a new ejection–absorption heat transformer is presented and analyzed in this paper. The results show that it has a simpler configuration than the double absorption heat transformer and two-stage heat transformer. The delivered useful temperature in the ejection–absorption heat transformer is higher than for a single stage heat transformer and simultaneously its system performance is raised.     

Enhanced reversible hydrogen storage properties of a Mg–In–Y ternary solid solution

A Mg(In, Y) ternary solid solution was successfully synthesized by two-step method, namely sintering the elemental powders and subsequent milling. The formation of Mg(In, Y) indicates that the solubility of Y in the Mg lattice is expanded due to the existence of In. The as-synthesized Mg₉₀In₅Y₅ solid solution transformed to MgH₂, YH₃, In₃Y and MgIn compound upon hydrogenation, the hydrogenated products except for the YH₃ recovered to Mg(In, Y) solid solution after dehydrogenation. The Mg₉₀In₅Y₅ solid solution exhibited a decreased reaction enthalpy of 62.9 kJ/(mol H₂), reduction by ca. 5 kJ/(mol H₂) or 12 kJ/(mol H₂) than the Mg₉₅In₅ binary solid solution and pure Mg, respectively. The working temperature as well as the activation energies for the hydriding and dehydriding were also decreased in comparison with those of Mg(In) binary solid solution, which are attributed to the reduced reaction enthalpy and the catalytic role of YH₃. Our work indicates that the thermodynamic and kinetic tuning of MgH₂ are realized in the Mg(In, Y) ternary solid solution.     

A water–water preheater and a steam–water heater network: Temperature dynamics

The dynamic simulation of an integrated, double pipe heat exchanger network was validated through experimentation. A steam–water, concentric tube, heat exchanger was coupled to a water–water preheater. When the preheater was configured for cocurrent flow with equal fluid velocities in its annulus and core, Lagrangian-based derivations yielded analytical solutions that accurately predicted observed temperature dynamics. When the preheater was configured for countercurrent flow with distinct fluid velocities in its annulus and core, analytical solutions for the heater and connecting tubing were coupled with Eulerian based numerical solutions for the preheater. Programming used Mathcad. Nonlinear regression analysis of steady state data was used to determine system parameters. The significance of time delays through the integration of unit operations is illustrated.     

A non-isothermal model of a nickel–metal hydride cell

A model for a nickel–metal hydride cell was constructed based on the planar electrode approximation. The mass balances of active species, the kinetics of electrochemical reactions, the ohmic effects of internal resistance, and the energy balance of the whole cell were considered in the model. An empirical approach was utilized to account for the hysteresis potential behavior of the nickel electrode. The model predictions showed favorable agreement with the experimental data.     

Combustion characteristics of a lean premixed LPG–air combustor

Fuel/air mixing effects in a premixer have been examined to investigate the combustion characteristics, such as the emission of NO_x and CO, under simulated lean premixed gas turbine combustor conditions at normal and elevated pressures of up to 3.5 bar with air preheat temperature of 450 K. The results obtained have been compared with a diffusion flame type gas turbine combustor for emission characteristics. The results show that the NO_x emission is profoundly affected by the mixing between fuel and air in the combustor. NO_x emission is lowered by supplying uniform fuel/air gas mixture to the combustor and the NO_x emission reduces with decrease in residence time of the hot gases in the combustor. The NO_x emission level of the lean premixed combustor is a strong function of equivalence ratio and the dependency is smaller for a traditional diffusion flame combustor under the examined experimental conditions. Furthermore, the recirculation flow, affected by dome angle of combustor, reduces the high temperature reaction zone or hot spot in the combustor, thus reducing the NO_x emission levels.     

Gas–Liquid Two-Phase Flow Evolution in a Long Microchannel

A pair of optical void sensors and a high-speed video camera were used to investigate the evolution of adiabatic gas–liquid two-phase flow in a long microchannel. Experiments were conducted with a 1676-mm-long, circular microchannel with an inner diameter of 100 μm. Two-phase flow patterns, void fraction, and velocities of gas plug/slug and liquid slugs were measured at different axial locations between the gas–liquid mixer and microchannel exit. The pressure decreased linearly in the first half of the microchannel, and more rapidly and nonlinearly in the second half of the test section. As a result, the flow accelerated significantly in the second half of the microchannel such that the void fraction and liquid slug velocity increased nonlinearly. The measured mean void fraction and mean velocity of liquid slugs also agreed well with the homogeneous flow model predictions when the liquid flow rate was constant and the mass velocity of the gas was low.     

Simulation of a Turbulent Impinging Jet into a Layer of Porous Material Using a Two–Energy Equation Model

This article presents numerical results for a turbulent jet impinging against a flat plane covered with a layer of permeable and thermally conducting material. Distinct energy equations are considered for the solid porous material attached to the wall and for the fluid that impinges on it. Parameters such as Reynolds number, porosity, permeability, thickness, and thermal conductivity of the porous layer are varied in order to analyze their effects on the local distribution of Nu. The macroscopic equations for mass, momentum, and energy are obtained based on volume-average concept. The numerical technique employed for discretizing the governing equations was the control volume method with a boundary-fitted nonorthogonal coordinate system. The SIMPLE algorithm was used to handle the pressure-velocity coupling. Results indicate that inclusion of a porous layer eliminates the peak in Nu at the stagnation region. For highly porous and highly permeable material, simulations indicate that the integral heat flux from the wall is enhanced when a thermally conducting porous material is attached to the surface.     

Hydrogen embrittlement associated with strain localization in a precipitation-hardened Fe–Mn–Al–C light weight austenitic steel

Hydrogen embrittlement of a precipitation-hardened Fe–26Mn–11Al-1.2C (wt.%) austenitic steel was examined by tensile testing under hydrogen charging and thermal desorption analysis. While the high strength of the alloy (>1 GPa) was not affected, hydrogen charging reduced the engineering tensile elongation from 44 to only 5%. Hydrogen-assisted cracking mechanisms were studied via the joint use of electron backscatter diffraction analysis and orientation-optimized electron channeling contrast imaging. The observed embrittlement was mainly due to two mechanisms, namely, grain boundary triple junction cracking and slip-localization-induced intergranular cracking along micro-voids formed on grain boundaries. Grain boundary triple junction cracking occurs preferentially, while the microscopically ductile slip-localization-induced intergranular cracking assists crack growth during plastic deformation resulting in macroscopic brittle fracture appearance.