1,721,033 research outputs found
Topology optimization as a powerful tool to design advanced PEMFCs flow fields
Full text linkThis paper presents a thorough and affordable numerical framework to design the flow field of Proton Exchange Membrane Fuel Cells using topology optimization. No assumption is made about the layout of the channels, which freely evolves along the optimization process, resulting in non-trivial optimized geometries. The optimization problem is formulated to maximize both the power generation and homogeneity of current density distribution, in the spirit of reduced costs and increased durability. The evolution of the flow field geometry is computed with a gradient-based optimizer with gradients of the objective and constraints computed through the discrete adjoint method. At each optimization iteration, the incompressible Navier-Stokes, advection-diffusion, and Butler-Volmer equations are solved with a 2D finite element model that predicts the flow in the channels, transport of chemical species and electrochemical reactions. The 3D transport effects are accounted for in the 2D model through an original depth-averaging procedure. The results of the 2D prediction are verified against a full 3D model calibrated using numerical and experimental results. The developed design framework can be used to identify flow field layouts that outperform current industrial solutions, catch design trends and provide guidelines to technology practitioners. The topology-optimized designs yield significant power generation enhancements, an improved reactant distribution and a reduced pressure drop as compared to conventional flow fields. Increasing the inlet pressure leads to more and more intricate configurations with complex topologies and highly tortuous channels. However, the cell performance is found to be more sensitive to the topology of the flow distributor at low rather than at high inlet pressures. Considering a measure of the current density homogeneity in the optimization objective allows the identification of layouts in which the gas channels concentrate close to the outlets rather than close to the inlet. These design features slightly affect the amount of power generated, suggesting a viable route for future technological development
Novel Gas Diffusion Layers with Patterned Wettability for Advanced Water Management Strategies in Polymer Electrolyte Fuel Cells
No full textModelling of corrosive trace components in a GTL facility using UniSim
No full textGas-To-Liquid (GTL) technology, first conceptualized at Shell Amsterdam laboratory in 1973, is a route to make liquid fuels and chemical products from natural gas instead of using crude oil. A large range of products result from the GTL process: base oils, gasoil, kerosene, naphtha, normal paraffins and waxes. The nature of GTL process results in a very pure high-quality synthetic products, allowing the reduction of particulate, NOx, SOx and aromatics emissions which are released during fuels combustion. The emissions levels are lower than those seen when using the liquids fuels produced from crude oil. Corrosive trace components in the effluents of a Fischer-Tropsch unit can be a process safety threat in the downstream section of a gas to liquids facility. Hence, the prediction of the concentrations of these trace components throughout the facility is key as it allows to define the right inspection program or to determine whether other measures are required to reduce risk of loss of containment. The corrosive species are not implemented yet in the integrated simulation model of the GTL process, therefore the aim of this project is modelling the corrosive trace components in the effluents of Fischer-Tropsch unit to predict their concentrations at the plant, including the locations where it is not possible to inspect or take samples. By tracking the species, it is possible to provide data that helps with ongoing research studies or predictive tools. The validation step is carried out by using the available samples from a commercial GTL plant. The model will enable a pro-active monitoring and maintenance of critical areas at GTL plants designed and operated by Shell
Development of membrane diagnostics and novel porous materials for next generation redox flow batteries
Full text linkEmbargo 1 year, pdf open access 21-2-202
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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