1,720,993 research outputs found
Thermo-economic analysis of the energy storage role in a real polygenerative district
No full textThis paper presents a thermo-economic analysis based on data from a real Smart polygeneration microgrid (SPM), designed to satisfy energy demands of the university campus of Savona (Italy). The plant is made up of different cogenerative generators (micro gas turbines and an internal combustion engine), renewable generators and two auxiliary boilers (one of them is off during the most of the time): the generators are “distributed” around the campus and coupled to electrical and thermal storages. Since several cogenerative units are included in the grid, the integration of the different storage systems is relevant in order to determine the best management strategy, following both thermal and electrical requests and taking into proper account the strong difference between the two energy demand profiles.
The thermo-economic analysis is performed exploiting the software W-ECoMP, developed by the authors’ research group, in order to find the best operational strategy, considering the importance of an appropriate storage system to manage the polygenerative energy district; attention is paid to the integration and combination of three different kinds of storage (hot and cold water tanks and electrical battery). Different scenarios are presented, combining the storages and showing their impact in terms of money savings and reduction of electrical energy purchasing from the National grid. Both the grid connected mode and island mode of operation of the SPM are considered.
The analysis is performed considering the time dependent nature of the energy demands throughout the whole year and implementing the experimental off-design curves of the real devices installed in the grid
Performance analysis of PTES layouts evolving sCO2 for industrial WHR integration
No full textA consistent amount of renewable energy (RES) from nonpredictable sources in the energy mix brings an increasing need of energy storage technologies to support grid stability. At the same time, electrification of industrial processes as well as the more and more common habit of industries to self-produce power via RES or CHP, can make industries a partner in disrupting grid stability. Thermo-mechanical storages can contribute through the use of traditional technologies (rotating machinery) employed in power plants, which are currently used to manage peak demand and grid services, and typically classify as hours-size storages, also capable of providing spinning reserve services to the electrical grid. Among such type of storages, Pumped Thermal Energy Storages (PTES) are a promising technology that enhance the concept of power-toheat-to-power and long duration energy storage, and presents also different layouts and applications. This paper analyse the thermal performance of Pumped Thermal Electricity Storage (PTES) evolving supercritical CO2 (sCO2), comparing different layouts, while valorising waste heat (WH) sources, which are typically in temperature ranges of 100-400°C. WH temperature in this range are difficult to be exploited for traditional energy generation, but they are currently under investigation for the possibility to be valorised via High Temperature Heat Pump. In this sense this quality of Waste Heat could be valorised via PTES. In fact, the use of additional heat, otherwise dumped to ambient, may make the system capable of an apparent round-trip efficiency (RTE) higher than 100%. The use of sCO2 could enhance the techno-economic features of these systems, if compared to similar plants evolving steam or air. Starting from an identified reference case (a cement production plant with WH temperature to be valorized around 350°C), a sCO2-based PTES cycle is presented and analysed in this paper. The waste heat integration to the PTES system has been found to add an undeniable value in terms of RTE. The use of sCO2 enhances the techno-economic features of these systems, the independent charging and discharging system proposed in this study can also provide a keen sense of flexibility. At the same time, the valorisation of low temperature waste heat enables industries to enhance their energy efficiency, limit their operational costs and environmental impact, whilst becoming an active part in the regulation of the grid. Nevertheless, CAPEX of the proposed systems are still quite relevant and only a robust exploitation of the PTES in ancillary service market could attract industrial customers interest on sCO2 PTES
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
Theoretical investigation of a novel high-temperature heat pump exploiting low-temperature waste heat and using two-phase machines with zero electric consumption
No full textA novel high-temperature heat pump (HTHP) exploiting low-temperature waste heat is presented, which is enabled by two-phase compressors and expanders without the need for any requirement of external electric power. The investigation involves a sensitivity analysis at the design point, considering the concurrent variation of five independent variables. The aim is to identify the best-performing conditions for a rubber manufacturer and a canning industry which have different temperatures of waste heat and required heating power. The COP of the overall HTHP system, which is the ratio between the output heating power and the input thermal power (coming from the heat source) is evaluated. The maximum COP values are 0.258 for the rubber manufacturer and 0.452 for the canning industry. The primary energy saving is assessed in terms of equivalent fuel consumption. For the rubber manufacturer, the resulting yearly cost saving is in the range of 129 & DIVIDE; 646 euro/kWth of HTHP installed capacity, and 140 euro/kWth for the canning industry. The economic viability of the HTHP is contingent upon achieving isentropic efficiencies of the expanders and compressors higher than 0.59 and 0.55, respectively, for the rubber manufacturer, and both higher than 0.45 for the canning industry
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
A prototype recuperated supercritical CO<sub>2</sub> cycle : Part-load and dynamic assessment
No full textHigh efficiency, flexibility and competitive capital costs make supercritical CO2 (sCO2) systems a promising technology for renewable power generation in a low carbon energy scenario. Recently, innovative supercritical systems have been studied in the literature and proposed by DOE-NETL (STEP project) and by a few projects in the EU Horizon 2020 (H2020) program aiming to demonstrate supercritical CO2 Brayton power plants, promising superior techno-economic features than steam cycles particularly at high temperatures. The H2020 SOLARSCO2OL project, which started in 2020, is building the first European MW-scale sCO2 demonstration plant and has been specifically tailored for Concentrating Solar Power (CSP) applications. After a detailed explanation of the modelling approach for steady and unsteady cycle simulations, this paper presents the off-design and dynamic analysis of such plant layout, which is based on a simply recuperated sCO2 cycle. The entire system model has been developed in TRANSEO environment. The part-load analysis ranged from 50% of nominal up to a 105% peak load, discussing the impact on compressor and turbine operating conditions. Full operational envelop has been determined considering cycle main constraints, such as maximum turbine inlet temperature and minimum pressure at compressor inlet. The off-design performance analysis highlights the most relevant relationships among the main part-load regulating parameters, namely molten salt mass flow rate, CO2 mass flow rate, total CO2 mass in the loop, and shaft line speed. The results show specific features of different control approaches, discussing the pros and cons of each solution, considering also its upscale towards commercial applications. In particular, the analysis shows that at 51% of load an efficiency decrease of 20% is expected. Finally, the dynamic characterization of the closed loop shows the relatively fast responsiveness of the plant to compressor speed variations, causing quick changes in CO2 mass flow rate, together with longer time scale phenomena related to the plant heat exchangers. In this respect, sCO2 plants demonstrate to have the potential to provide primary reserve for the electrical grid, as far as thermal stresses on main plant components are kept under acceptable limits.</p
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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