1,720,956 research outputs found
Trigenerative micro compressed air energy storage: Concept and thermodynamic assessment
No full textEnergy storage is a cutting edge front for renewable and sustainable energy research. In fact, a massive exploitation of intermittent renewable sources, such as wind and sun, requires the introduction of effective mechanical energy storage systems.In this paper we introduce the concept of a trigenerative energy storage based on a compressed air system. The plant in study is a simplified design of the adiabatic compressed air energy storage and accumulates mechanical and thermal (both hot and cold) energy at the same time. We envisage the possibility to realize a relatively small size trigenerative compressed air energy storage to be placed close to the energy demand, according to the distributed generation paradigm. Here, we describe the plant concept and we identify all the relevant parameters influencing its thermodynamic behavior. Their effects are dissected through an accurate thermodynamic model. The most relevant technological issues, such as the guidelines for a proper choice of the compressor, expander and heat exchangers are also addressed. Our results show that T-CAES may have an interesting potential as a distributed system that combines electricity storage with heat and cooling energy production. We also show that the performances are significantly influenced by some operating and design parameters, whose feasibility in real applications must be considered
Technical and economic assessment of a SOFC-based energy system for combined cooling, heating and power
No full textHere we present the technical and economical performances of a small scale trigeneration power plant based on solid oxide fuel cells and designed for a small residential cluster (i.e. 10 apartments). The energy system features a natural gas solid oxide fuel cell, a boiler, a refrigerator, and a thermal storage system. We compare different power plant configurations varying the size of the fuel cell and the refrigeration technology to satisfy the chilling demand (i.e. absorption or mechanical chiller). Given that the ability to meet the power demand is crucial in this kind of applications, the plant performances are assessed following an optimal control strategy, as a function of different energy demand profiles and electricity prices, and of rated and part load efficiencies of each energy converter. The optimization of the energy system operating strategy is performed through a graph theory-based methodology. Results are provided in terms of electrical and thermal efficiency, operating strategy, as well as economic saving, primary energy consumption reduction, and pay back period, considering different capital costs of the fuel cell
Analysis of the influence of Thermal Energy Storage on the Optimal Management of a Trigeneration Plant
Full text linkSafety, security, and sustainability of energy supply chains are among the main concerns of industrialized countries, and, therefore, distributed generation has significantly increased its share of the energy market, thanks to the possibility to simultaneously meet electrical, thermal and cooling demand, thus increasing the overall source-to-final-use conversion efficiency. The efficiency of a distributed generation system is influenced both by the individual performance of the plant components as well as by their interconnection, and is very sensitive to the control strategy adopted in the different plant sections. This last remark is particularly relevant for distributed generation systems, that are subject to rapid gradients in both the thermal and electrical loads, and in the values of the energy vector. In this respect, the introduction and the correct management of energy storage systems is a key point for trigeneration plants. In fact, energy storage brings on the one side advantages as for the reduced components sizes, but more importantly allows for a substantial decoupling of the thermal and electrical demands, making load following less of a stringent requirement. An optimization methodology, based on energy fluxes simulation, and on the application of the graph theory as in previous works by some of the authors, is used to identify the optimal set-points for each component. The optimization algorithm searches for the plant management envelope that minimizes a prescribed objective function. Specifically, two different optimization criteria are considered: i) economic optimization that minimizes the total daily operating cost and ii) primary energy use optimization, that minimizes the total daily amount of primary energy used by the plant. Since the paper focus is on the effects of energy storage, the trigeneration plant behavior will be analyzed both in terms of economical results and in terms of efficiency and primary energy use
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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