1,720,961 research outputs found
ENGINEERING UNIVERSAL STACKS FOR LONG DURATION ENERGY STORAGE FLOW BATTERIES
No full textVanadium Flow Batteries (VFBs) have already hit the market with several GW/GWh systems installed worldwide. The growing market demand for long duration energy storage (LDES) systems, linked to the increasing diffusion of
renewable sources, requires high-performance and economically convenient technologies. This has led numerous research initiatives across major countries to develop innovative, efficient, accessible, and cost-effective active chemical species for their use in flow batteries. However, there has been comparatively little effort dedicated to advancing high-performance technology to take full benefit from these chemistries. This gap poses the risk that inadequate flow battery engineering may hinder the potential success of emerging new flow battery chemistry or even lead to industrial and commercial failure of start-ups and industries. The goal of this work is to develop an electrochemical reactor that fully harnesses the potential of various chemistries, to allow interested companies to quickly and effectively enter the market. The opportunity to develop a universal stack comes from the fact that different flow batteries share the same active materials, membrane and electrodes, and therefore the same cell configuration. This thesis presents the process for the design, construction and testing of a universal redox flow battery stack, capable of operating with different active chemical species. Polarization curves on a mid-size single cell were obtained to identify high performance commercial active materials, as well as to investigate their chemical stability over prolonged charge and discharge cycles. The experimental analysis was coupled with CFD simulations to evaluate the fluid dynamics of large flow battery cells during full-load charging and discharging under critical conditions, with vanadium electrolyte and organic electrolyte. The fluid dynamic analysis enabled important drivelines to guide the mechanical design of the stack that was performed through advanced CAD software for assembly and tolerance analysis. The stack designed in this work was then hydraulically validated. In the framework of investigating new chemistries, a techno-economic comparison between all-vanadium and all-iron flow batteries was performed. This analysis aims to highlight the potential of all-iron flow batteries as innovative and competitive solutions for LDES applications, while exploring strategies to reduce their production costs. Finally, an investigation on the impact of electrolyte mixing, inside vanadium flow battery tanks, on capacity degradation was performed using various inner tank structures. This thesis represents one of the first studies on the scale-up process for high performance electrochemical stack. In general, the results presented are new and aim to cover the gap between research and industry in view of widespread flow battery commercialization
Prospects for industrial vanadium flow batteries
Get PDFVanadium Flow Batteries (VFBs) are a stationary energy storage technology, that can play a pivotal role in the integration of renewable sources into the electrical grid, thanks to unique advantages like power and energy independent sizing, no risk of explosion or fire and extremely long operating life. The first part of this paper presents the main features and the basic performance parameters of VFB, which determine their electric, hydraulic, thermal, and aging feature. The latter part outlines the strengths and weaknesses of the technology, the services that it can provide to the grid, and a short economic analysis. After presenting the fundaments of the technology, prospects and trends of VFBs deployment are outlined. Most of the considerations highlighted in this paper are inspired to studies performed on an industrial-size VFB operated at the Electrochemical Energy Storage and Conversion Lab (EESCoLab) at the University of Padua (Italy)
Electrical Characterization of Vanadium Flow Battery-Cell Test Facility (VFB-CTF): Early Results and Methods for Scaling Up
No full textExperiment-supported survey of inefficient electrolyte mixing and capacity loss in vanadium flow battery tanks
No full textThis study investigates the impact of electrolyte mixing inside the tanks of Vanadium Flow Battery (VFB) on capacity degradation. Heterogeneous mixing inside the tanks may lead to a severe capacity drop due to the existence of stagnant electrolyte regions and asymmetries in the State of Charge (SoC) of the positive and negative electrolytes reaching the cell. The study is based on a preliminary order-of-magnitude analysis involving the dimensionless Richardson and Reynolds numbers. A subsequent experimental campaign is carried out in which cell voltage and current response are screened for different tank designs and operating conditions to identify different fluid-dynamics events in the tanks. The results highlight the two main competing phenomena affecting the electrolyte fluid dynamics: buoyancy effects induced by density variations, and the inertia of the inlet submerged jet. The interplay between these two forces determines the flow field and therefore the SoC of the electrolyte feed to the cell, which affects the usable capacity and battery performance. Inertia dominated flows induce homogeneous electrolyte mixing, leading to a higher usable capacity, whereas buoyancy dominated flows result in a lower one. Furthermore, various inner structures were tested within the tanks to optimize mixing. These structures were created using additive manufacturing techniques. The implementation of helicoidal geometries within the tanks, promoting longer electrolyte paths and ample cross-sectional areas for convective mixing, markedly enhanced battery capacity compared to traditional empty tanks. These findings call for further investigation into optimizing the geometry of large-scale (VFB) storage tanks
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
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