1,721,043 research outputs found
Wind-hydrogen energy stand-alone system with carbon storage: Modeling and simulation
No full textA wind-hydrogen hybrid system with carbon physisorption storage has been developed and implemented within a dynamic model-based software environment. Numerical simulations have been applied to synthetic and real data to evaluate its operations and performance over a 6-month period. Hydrogen is yielded by electrolysis with energy converted from wind, and load is powered either by direct turbine connection, by battery or a fuelcell. Surplus hydrogen is stored by physisorption in a cluster of nitrogen-cooled tanks filled with activated carbons. Physisorption has been modeled after the Ono-Kondo isotherm from laboratory data available in literature. The operating cycle is composed of four transformations: isobar pre-charging at 0.1MPa, isothermal charging at 77K, isobar pre-discharging at 6 MPa, and isothermal discharging at 153K. From our simulation runs, the system can operate as stand-alonegranting total independence from the grid. The storage system has good gravimetric and volumetric capacity(10.8%and 32.5g/l at 6 MPa). Overall system efficiency is estimated to be around 10%. Hydrogen physisorption on carbon seems a potentially feasible storage technique for hydrogen with tanks that are compact and safe, hence apt for stationary and some non-stationary applications
Solar Hydrogen Energy Systems: Science and Technology for the Hydrogen Economy
No full textIt is just a matter of time when fossil fuels will become unavailable or uneconomical to retrieve. On top of that, their environmental impact is already too severe. Renewable energy sources can be considered as the most important substitute to fossil energy, since they are inexhaustible and have a very low, if none, impact on the environment. Still, their unevenness and unpredictability are drawbacks that must be dealt with in order to guarantee a reliable and steady energy supply to the final user. Hydrogen can be the answer to these problems. This book presents the readers with the modeling, functioning and implementation of solar hydrogen energy systems, which efficiently combine different technologies to convert, store and use renewable energy. Sources like solar photovoltaic or wind, technologies like electrolysis, fuel cells, traditional and advanced hydrogen storage are discussed and evaluated together with system management and output performance. Examples are also given to show how these systems are capable of providing energy independence from fossil fuels in real life settings
Modelling and simulation of a wind-hydrogen CHP system with metal hydride storage
No full textThis paper describes the modelling and simulation of a wind-hydrogen system aimed at supplying electrical and thermal residential loads, where the thermal load is in part supplied by a catalytic hydrogen combustion device with hydrogen stored in a metal hydride system composed of a cluster of five metal hydride tanks equipped with a metal foam heat exchanger.The complete mathematical model has been developed from models available in literature and describing the different sub-systems that constitute the overall wind-hydrogen system. It has been laterimplemented in a multi-domain software environment to simulate system operations.Results over a year-long simulation show complete stand-alone capabilities, with an electrical efficiency and a combined heat and power efficiency of 8.2% and 12.5% respectively. At the end of thesimulation period, a hydrogen annual surplus of 110.5 kg is left over which can, for instance, be used to feed a hydrogen powered car for about 9500 km
Design and Simulation of Activated Carbon Tanks for Hydrogen Storage
No full textWhile hydrogen production from renewable energy sources does not have real limiting drawbacks, storage instead poses serious questions on whether an adequate solution will ever be achieved. The Department of Energy (USA) set targets for non-stationary storage systems which prove difficult to meet: gravimetric capacity is targeted at 9% (3 kWh/kg) for year 2015. Such targets are though not binding for stationary applications, but still are considered the goal for H2 storage. Classic storage technology (compression, liquefaction) seems not to be the answer.To find alternative storage solutions, a complete hybrid system with hydrogen storage based on physical adsorption of hydrogen on activated carbons was modeled and simulated
Hybrid Systems for Solar Hydrogen: A Selection of Case-Studies
No full textTwelve case-studies on systems that generate, store and use hydrogen from photovoltaic energy are hereby presented and discussed. Hydrogen generated from direct sunlight is often called solar hydrogen, and the whole process is characterized by having very low CO2 and pollutants emissions. Such systems, comprising of several sub-systems of different technologies, are called hybrid systems. All case-studies are briefly analyzed and the most prominent conclusions reported. Results show that production of solar hydrogen and its subsequent use in fuel cells is technically viable but costs still need to be reduced for widespread adoption. A comparison is given and need for further work highlighted; in particular, researchers should investigate carbon structures as a potential alternative to pressurization or metal hydrides; a complete analysis of the intangible costs and benefits involved should be performed, together with Discounted Cash Flow and Life Cycle Assessment analysis to understand the true nature of such investments and their sustainability in the near future. Performing such a rigorous and complete economical analysis would, for instance, enable governments to design better incentive schemes and propel such technology in real life usage
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
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