High pressure physical solubility of carbon dioxide (CO2) in mixed polyethylene glycol dimethyl ethers (Genosorb 1753)

Solubility of carbon dioxide in a mixture of polyethylene glycol dimethyl ethers (Genosorb 1753) was determined at 298.15, 313.15, 323.15 and 333.15 K at pressures up to 7940 kPa. The obtained solubility data are compared with those of CO₂ in other physical solvents. The results were correlated with the Peng–Robinson (Peng and Robinson, Ind. Eng. Chem. Fundam. 15, 59–64 1976) equation of state, and the interaction parameters are reported. Data at 323.15 K were predicted. Henry's Law constants were obtained from the data and the excess properties (excess Gibbs free energy, excess entropy and excess enthalpy) of the liquid mixture over the full range of composition were predicted at each temperature using the NRTL activity coefficient model. Enthalpy of solution and the enthalpy of mixing were determined at infinite dilution. In addition, the heats of absorption were determined using Clausius–Clapeyron equation. La solubilité du dioxyde de carbone (CO₂) dans un mélange de polyéthylène glycol diméthyl éthers (Genosorb 1753) a été déterminée à 298.15, 313.15, 323.15 et 333.15 K à des pressions allant jusqu'à 7940 kPa. Les données de solubilité obtenues sont comparées avec celles de CO₂ dans d'autres solvants physiques. Les résultats ont été corrélés avec l'équation d'état de Peng–Robinson (Peng and Robinson, Ind. Eng. Chem. Fundam. 15, 59–64 1976) et les paramètres d'interaction sont présentés. La solubilité à 323.15 K a été prédite. Les constantes de la loi d'Henry ont été obtenues à partir des données. Les propriétés en excès (l'énergie libre de Gibbs d'excès, l'entropie et l'enthalpie d'excès) du mélange liquide sur toute la gamme de composition a ont été prédites à chaque température en utilisant le modèle NRTL. L'enthalpie de solution et l'enthalpie de mélange ont été déterminées dilution infinie. Finalement, les chaleurs d'absorption ont été déterminées en utilisant l'équation de Clausius–Clapeyron. © 2011 Canadian Society for Chemical Engineering     

Prediction of the performance of a solid oxide fuel cell fuelled with biosyngas: Influence of different steam-reforming reaction kinetic parameters

SOFCs are often designed to operate with specific fuels, quite often natural gas. CFD modeling is often used to arrive at efficient and safe SOFC designs. Therefore, when an SOFC is fed with different fuels, i.e., biosyngas, CFD can be used as a tool to predict whether the cell and stack will be safe and operate efficiently, and thus can give suggestions for the operation strategies for SOFCs. For that reason, a combined mass and heat transport model of an SOFC (single channel) has been developed for an anode-supported SOFC fed with biosyngas with special attention to the reaction kinetics of the direct internal reforming (DIR) reaction together with the water–gas shift reaction. An SOFC design jointly developed by ECN and Delft University of Technology is employed for the calculations. This work aims to predict the influence of different reforming reaction kinetic parameters on the cell performance by using an anode-supported intermediate temperature DIR planar solid oxide fuel single channel model, under co-flow operation. The DIR reaction of methane, the water–gas shift reaction and the electrochemical oxidation of hydrogen are being considered. As different reaction kinetic models are available in literature and employing them in CFD calculations will yield different results, a comparative analysis is carried out. Several cases were studied with a variety of DIR and water gas shift reaction kinetic parameters available from literature. For the different cases considered, the modeling results show differences in the current density distribution and temperature profile in the channel and in gas concentration profile along the channel. These differences are presented and discussed in detail. Predictions of the behaviors of internal reforming reaction in the reaction zone, and the possibilities of unwanted side reactions such as carbon deposition and Ni oxidation are given with constructive suggestions for future lab experiments.     

Anode recirculation behavior of a solid oxide fuel cell system: A safety analysis and a performance optimization

Anode recirculation, which is generally driven by an ejector, is commonly used in solid oxide fuel cell (SOFC) systems that operate with natural gas. Alternative fuels such as gasification syngas from biomass have been proposed for potential use in the SOFC systems because of the fuel flexibility of SOFCs and the sustainability of biomass resources. Because the ejector was initially designed to use natural gas, its recirculation behavior when using alternative fuels is not well understood. The aim of this research work is to study anode recirculation behavior and analyze its effect on safety issues regarding carbon deposition and nickel oxidation and the performance of an SOFC system fed with gasification syngas under steady state operation. We developed a detailed model including a recirculation model and an SOFC stack model for this study, which was well validated by experimental data. The results show that the entrainment ratio with the gasification syngas is much smaller than that with the natural gas, and the gasification syngas does not have the tendency toward carbon deposition or nickel oxidation under the operating conditions studied. In addition, the recirculation affects the performance of the SOFC, especially the net electrical efficiency, which could be promoted by 160%.     

Optical and magnetic properties of copper doped ZnO nanorods prepared by hydrothermal method

Surfactant free ZnO and Cu doped ZnO nanorods were synthesized by hydrothermal method. The formation of ZnO:Cu nanorods were confirmed by scanning electron microscopy, X-ray diffraction and Raman analysis. Diffuse reflectance spectroscopy results shows that band gap of ZnO nanorods shifts to red with increase of Cu content. The orange-red photoluminescent emission from ZnO nanorods originates from the oxygen vacancy or ZnO interstitial related defects. ZnO:Cu nanorods showed strong ferromagnetic behavior, however at higher doping percentage of Cu the ferromagnetic behavior was suppressed and paramagnetic nature was enhanced. The presence of non-polar E ₂ ^high and E ₂ ^low Raman modes in nanorods indicates that Cu doping didn’t change the wurtzite structure of ZnO.     

System Study on Hydrothermal Gasification Combined With a Hybrid Solid Oxide Fuel Cell Gas Turbine

The application of wet biomass in energy conversion systems is challenging, since in most conventional systems the biomass has to be dried. Drying can be very energy intensive especially when the biomass has a moisture content above 50 wt.% on a wet basis. The combination of hydrothermal biomass gasification and a solid oxide fuel cell (SOFC) gas turbine (GT) hybrid system could be an efficient way to convert very wet biomass into electricity. Therefore, thermodynamic evaluation of combined systems with hydrothermal gasification units and SOFC–GT hybrid units has been performed. Three hydrothermal gasification cases have been evaluated; one producing mainly methane, a second one producing a mixture of hydrogen and methane and the last one producing mainly hydrogen. These three gasification systems have been coupled to the same SOFC–GT hybrid system. All the integrated systems have electrical exergy efficiencies around 50%, therefore, the combination of supercritical water gasification and SOFC–GT hybrid systems seems promising. The overall system performance depends for a large part on the liquid gas separation. Further research is required for finding out the optimal separation conditions.     

Designing experiments to differentiate between adsorption isotherms using T-optimal designs

T-optimal experimental designs are developed to distinguish between the 3-parameter Guggenheim-Anderson-deBoer (GAB) and 2-parameter Brunauer-Emmett-Teller (BET) adsorption isotherms. The results show that the designs are not dependent on one of the GAB model parameters (the monolayer capacity, which is a linear scaling factor), but are dependent on the other two, which determine the curvature and shape of the isotherms. Further analysis of the designs show that for the range of model parameters considered, misspecification of the model parameters can reduce the efficiency of the experimental design to 30% or less: proper selection of the model parameters at which the design is developed within the model-parameter space can increase the maximum-minimum design efficiency to nearly 55%. The experimental replication inherent in T-optimal designs is then used in combination with a statistical lack-of-fit analysis to illustrate the role of experimental variability on the ability to distinguish between the two isotherm models.     

Thermodynamic Analysis of Solid Oxide Fuel Cell Gas Turbine Systems Operating with Various Biofuels

Solid oxide fuel cell–gas turbine (SOFC‐GT) systems provide a thermodynamically high efficiency alternative for power generation from biofuels. In this study biofuels namely methane, ethanol, methanol, hydrogen, and ammonia are evaluated exergetically with respect to their performance at system level and in system components like heat exchangers, fuel cell, gas turbine, combustor, compressor, and the stack. Further, the fuel cell losses are investigated in detail with respect to their dependence on operating parameters such as fuel utilization, Nernst voltage, etc. as well as fuel specific parameters like heat effects. It is found that the heat effects play a major role in setting up the flows in the system and hence, power levels attained in individual components. The per pass fuel utilization dictates the efficiency of the fuel cell itself, but the system efficiency is not entirely dependent on fuel cell efficiency alone, but depends on the split between the fuel cell and gas turbine powers which in turn depends highly on the nature of the fuel and its chemistry. Counter intuitively it is found that with recycle, the fuel cell efficiency of methane is less than that of hydrogen but the system efficiency of methane is higher.     

Subnanometer ga(2)o(3) tunnelling layer by atomic layer deposition to achieve 1.1 v open-circuit potential in dye-sensitized solar cells

Herein, we present the first use of a gallium oxide tunnelling layer to significantly reduce electron recombination in dye-sensitized solar cells (DSC). The subnanometer coating is achieved using atomic layer deposition (ALD) and leading to a new DSC record open-circuit potential of 1.1 V with state-of-the-art organic D-π-A sensitizer and cobalt redox mediator. After ALD of only a few angstroms of Ga(2)O(3), the electron back reaction is reduced by more than an order of magnitude, while charge collection efficiency and fill factor are increased by 30% and 15%, respectively. The photogenerated exciton separation processes of electron injection into the TiO(2) conduction band and the hole injection into the electrolyte are characterized in detail.     

Magnetic field enhanced resonant tunneling in a silicon nanowire single-electron-transistor

We report fabrication, measurement and simulation of silicon single-electron-transistors made on silicon-on-insulator wafers. At T-2 K, these devices showed clear Coulomb blockade structures. An external perpendicular magnetic field was found to enhance the resonant tunneling peak and was used to predict the presence of two laterally coupled quantum dots in the narrow constriction between the source-drain electrodes. The proposed model and measured experimental data were consistently explained using numerical simulations.     

Synthesis and thermal transport studies of nanofluids based on metal decorated photochemically oxidized multiwalled carbon nanotubes

Nanoparticle fluid suspensions were prepared using photochemically functionalized multiwalled carbon nanotubes in polar base fluids. Multiwalled carbon nanotubes prepared by catalytic chemical vapour deposition technique have been functionalized by irradiating with ultraviolet light of wavelength 254 nm. The photochemical oxidation of multiwalled carbon nanotubes under UV irradiation introduces oxygen containing functional groups onto the surface of the nanotubes, generating new defects on their structure. Silver nanoparticles have been deposited over multiwalled carbon nanotubes by chemical method. The enhancement in thermal conductivity of the prepared nanofluids using functionalized multiwalled carbon nanotubes and Ag nanoparticles deposited functionalized multiwalled carbon nanotubes with volume fraction, temperature and aspect ratio has been demonstrated. Silver deposited functionalized multiwalled carbon nanotubes based nanofluids in DI water with 0.02% volume fraction exhibit a thermal conductivity enhancement of 9.9% and 47% at room temperature and at 50 degrees C respectively.