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Development of innovative flow fields in a vanadium redox flow battery: Design of channel obstructions with the aid of 3D computational fluid dynamic model and experimental validation through locally-resolved polarization curves
Get PDFDistribution of the electrolyte over the porous electrode is a critical issue limiting the power density of vanadium redox flow batteries. The flow field design involves a trade-off among high battery performance, low pressure drops, reduced electrolyte imbalance and thus the understanding of the physical phenomena regulating mass transport of the electrolyte is crucial to develop improved flow fields. This work firstly presents the development of a 3D computational fluid dynamic model that couples fluid dynamic analysis of the electrolyte with the electrochemistry of the reactions involved. The model simulates the influence of both single serpentine and interdigitated flow field. After extensive validation with respect to local polarization curves in symmetric cell with both positive and negative electrolyte, the model is used to design flow fields with two different channel obstructions: the first one is located at the channel wall, while the second one is placed close to electrode interface. Both obstructions create a localized pressure difference between adjacent channels, enhancing electrolyte permeation through porous electrode. Finally, model predictions are verified experimentally: considering cycling operation at different operating current densities, the second obstruction is more effective in obtaining a good trade-off among performance, pressure drops and evolution of exchanged capacity
Unravelling the Contribution of Kinetics and Mass Transport Phenomena to Impedance Spectra in Vanadium Redox Flow Batteries: Development and Validation of a 1D Physics-Based Analytical Model
Get PDFVanadium redox flow battery technology can support the spread of energy storage in stationary applications and allow higher penetration of renewables in the electric grid. Currently, its market competitiveness is hindered by low power density, which stems from complex interplay between kinetic and mass transport losses. The quantitative interpretation of experimental observations should rely on physics-based models, which allow a consistent comparison of different operative conditions. In this work, a fast analytical physics-based 1D model of the impedance of vanadium flow battery is presented and validated with respect to experimental data. The model, made available online at http://mrtfuelcell.polimi.it, employs a macro-homogeneous approach and considers losses due to kinetics, reactant distribution within the electrode (Sigracet® SGL 39 AA carbon paper), convection in flow channel and vanadium transport to electrode surface. Additionally, analytical expressions of contributions to impedance of single physical phenomena are derived through an asymptotical analysis. The results show that, at negative electrode, transport of ions to active surface is the limiting phenomenon at lower flow rates, while at higher flow rates depletion of reactants within electrode becomes critical together with charge transfer processes. At positive electrode, the main contribution to performance loss is the vanadium transport to electrode surface
Investigation of vanadium redox flow batteries performance through locally-resolved polarisation curves and impedance spectroscopy: Insight into the effects of electrolyte, flow field geometry and electrode thickness
No full textThe inhomogeneous distribution of electrolyte over the porous electrode is one of the main issues hindering vanadium flow battery performance, limiting the system power density. Moreover, the interplay between fluid dynamics in distribution channels and morphology of porous electrodes is not well understood at local level throughout the cell active area, where local reactant starvation may occur and further limit system performance. Therefore, a systematic local characterization is fundamental to improve the understanding of system operation and to enhance system power density. This work discusses the implementation of a 10 regions macro-segmented flow battery with 25 cm2 active area, that permits the local measurement of polarisation curves and impedance spectra. Both positive and negative symmetric cells, as well as all-vanadium configuration, are adopted, combining carbon paper electrodes of different thickness with single serpentine and interdigitated distributors. The characterization evidences that single serpentine presents poor performance towards cell outlet, while interdigitated geometry is limited in the central region of active area. In most of the investigated operating conditions, single serpentine induces a more heterogeneous operation, especially if coupled with thinner electrode and positive electrolyte. Moreover, the representativeness at local level of symmetric cells compared to all-vanadium one is analysed and discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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