1,720,955 research outputs found
Analysis of flow field design on vanadium redox flow battery performance: Development of 3D computational fluid dynamic model and experimental validation
Full text linkHomogeneous distribution of the electrolyte over the porous electrode is a critical issue hindering the commercialization of vanadium redox flow batteries, owing to increased overpotential at high current and limited power density of the system. Therefore, an understanding of the physical phenomena regulating mass transport
of the electrolyte is crucial to improving system performance. The present work describes the development and experimental validation of a 3D computational fluid dynamic model of a vanadium redox flow battery in a half cell configuration with an active area of 25 cm2. The model simulates the influence of a single serpentine and an
interdigitated flow field. The adoption of the half-cell configuration allows the negative electrode to be considered as a pseudo-reference electrode with zero potential loss, leading to a reduction in computation time and the number of fitting parameters, which can be determined with reduced uncertainty. The developed model includes a traditional fluid dynamic analysis of the electrolyte in the flow field and in the porous electrode, coupled with the electrochemistry of the reactions involved. In both the experiments and the simulations, the single serpentine distributor exhibits better performance and higher pressure drops compared to those of the interdigitated geometry under all the investigated operating conditions. In the analysis of the local reaction rate, both distributors experienced increased reaction rates under the rib, induced by a by-pass flow between adjacent channels. The reaction rate shows a highly heterogeneous distribution in the serpentine geometry, while it is more uniform in the interdigitated configuration
Analysis of flow field design in vanadium redox flow batteries through the development and validation of CFD codes
Full text linkLAUREA MAGISTRALELa recente penetrazione di fonti rinnovabili all’interno del sistema energetico ha causato
un cambiamento nelle necessità del sistema di distribuzione e ha messo in luce l’esigenza
di sistemi di accumulo per bilanciare la rete. Tra i dispositivi elettrochimici, le batterie
a flusso al vanadio rappresentano una delle migliori tecnologie a causa della loro alta
efficienza, la lunga vita utile, l’affidabilità e l’indipendenza tra potenza installata e capacità
immagazzinata. La scarsa densità energetica e gli alti costi non permettono ancora
uno sviluppo su scala commerciale di questi sistemi, tuttavia sono presenti margini di
miglioramento.
Se la ricerca nel campo dei materiali porta allo sviluppo di componenti più performanti
ed economici, altri lavori sono intesi aumentare la prestazione del sistema attraverso
una gestione intelligente dell’architettura dello stack oppure ottimizzando il punto di
funzionamento. Questo lavoro quantifica l’impatto sulla prestazione della batteria di
un singolo componente, il distributore, e, per ottemperare a questo obiettivo, sono stati
sviluppati dei modelli numerici. La comprensione dei fenomeni fisici è intesa essere
strumento per l’ottimizzazione delle caratteristiche geometriche del distributore. Partendo
da una procedura di fitting usando un modello bidimensionale, un modello tridimensionale
capace di risolvere fluidodinamica ed elettrochimica sarà sviluppato usando un codice CFD
commerciale: "ANSYS Fluent ® ". Esso sarà usato per caratterizzare una cella idrogeno-vanadio
di 5 cm x 5 cm, un particolare setup sperimentale atto all’analisi delle perdite
del solo elettrodo positivo di batterie a flusso al vanadio. Saranno simulate differenti
geometrie, partendo da una geometria a serpentina e da una geometria in parallelo fino a
una geometria interdigitated, mentre una nuova geometria verrà proposta. E’ sviluppata
una procedura per quantificare tenendo conto dei consumi degli ausiliari l’efficienza del
sistema. Usando la cella idrogeno-vanadio presente nel laboratorio MRT Fuel Cell Lab,
quattro distributori sono testati per capire quale sia la miglior configurazione per il
distributore in un sistema reale e per validare sperimentalmente i risultati numerici.The recent penetration of renewable sources in the energy system caused a transformation
of the needs of the distribution system and amplified the need of energy storage systems
to properly balance the electricity grid. Among electrochemical energy storage devices,
all vanadium flow batteries are one of the most promising technologies due to their high
efficiency, long lifetime, reliability and independence between installed power and storage
capacity. Oppositely, the low energy density and the high costs are preventing this
technology from spreading at commercial level, even if many are the opportunities of
improvement.
If research on materials is working towards better and cheaper components, other works
are meant to improve the performance of the system by means of a smart stack configuration
or optimizing the operating condition. This work deals with the impact on the
performance of the battery of a single part of the system, the flow field, and, in order
to accomplish the desired purpose, numerical models have to be implemented and validated
on experimental data. The knowledge of the fluid dynamic and electrochemical
phenomena is intended as a tool for the optimization of the geometrical characteristics
of the flow field. Starting from a fitting procedure performed on a bidimensional model,
a threedimensional code to solve fluid dynamics and electrochemistry will be developed
using a commerical CFD code: "ANSYS Fluent". It will be used to characterize a 5 cm x 5
cm hydrogen-vanadium battery, a particular cell setup aimed at enlightening the losses
of just the positive electrode of a Vanadium Redox Flow Battery. Various geometries are
simulated, including a serpentine flow field, a parallel flow field and an interdigitated
flow field, while a novel geometry will be proposed. A dedicated procedure to analyze
the impact of the flow field considering both the electrochemical performance and the
pressure drop of the component is refined.
By means of the hydrogen-vanadium cell in MRT Fuel Cell Lab, four different flow fields
are tested to understand which could be the optimal flow field configuration in a real
system and to experimentally validate the numerical results
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
Business strategies for flexibility aggregators to steer clear of being “too small to bid”
Full text linkFlexibility aggregation is seen as a promising solution to facilitate the integration of solar and wind power into the energy system. While the solution is well known, it remains fairly uninvestigated in terms of the components needed to result in a business success. This study investigates the long-term business dynamics of flexibility aggregators with a simulation model. Our study finds that new entrants in flexibility markets are likely to be trapped in a “technology valley of death” situation on account of being “too small to bid”. Therefore, we test different strategies to overcome this critical initial phase. Diversifying revenue streams and introducing a leasing offer for flexible prosumers to enlarge the customer base are promising strategies to reach the relevant bidding size required to compete in balancing power markets. The analysis offers insights on the long-term uncertainties of the business case. The findings of this paper contribute to the discussion on how to develop functioning and robust business models for low-carbon flexibility. Furthermore, the study is of high practical relevance, as one of the burning questions for new entrants in flexibility markets is addressed with a concrete strategy analysis
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