1,720,960 research outputs found
Performance Analysis of Thermal Energy Storage (TES) Systems based on Sensible and Latent Heat for Concentrated Solar Power (CSP) Applications
No full textThe research on thermal energy storage (TES) systems carried
out by the Department of Mechanical, Chemical and Materials Engineering
(DIMCM) of the University of Cagliari focuses on sensible and latent heat.
In these last years, several research projects have concerned the
characterization of this kind of TES systems by developing mathematical
models, for simulating and predicting performance, and implementing
laboratory facilities. In particular, the last studies frame mainly in two
research projects. The first one concerns the performance evaluation of a
sensible heat TES system composed of a tank filled with solid beads
(packed bed) crossed by air used as heat transfer fluid (HTF). The second
one aims to compare the performance of latent heat TES systems of
different geometrical configurations. The present paper reports some
results, introduced by a brief description of the technology
A study of a packed-bed thermal energy storage device: test rig, experimental and numerical results
Full text linkThis paper presents the experimental set-up built at the DIMCM of Cagliari University to study a thermal energy storage (TES) system based on alumina beads freely poured into a carbon steel tank using air as heat transfer fluid. The system is instrumented with several thermocouples to detect axial and radial temperature distribution as well as reservoir wall temperature. Experimental temperature distribution along the storage system was compared with the numerical ones obtained by a two-phase one dimensional Schumann model. Numerical results show good agreement with the experimental results if thermal properties are considered as temperature dependent and the experimental temperature profile at the top of the bed is used for simulations
Pumped thermal energy storage systems integrated with a concentrating solar power section: conceptual design and performance evaluation
Full text linkA novel Pumped Thermal Energy Storage (PTES) system thermally integrated with a Concentrating Solar Power (CSP) plant is proposed and investigated. The two sections operate with the same working fluid, share several components and can operate simultaneously or independently of each other. A Thermal Energy Storage (TES) system composed of three thermocline packed-bed tanks is included. Specific mathematical models were developed to simulate the performance of the integrated PTES-CSP plant under nominal conditions and to evaluate the thermal profiles of the TES tanks. As a case study, an integrated PTES-CSP system characterized by a nominal power of 5 MW with a nominal storage capacity of 4 equivalent hours was considered. The influence of the main design parameters, namely the pressure ratio and the operating temperatures of the TES system, on the main performance indices was investigated. The results demonstrated that the exergetic roundtrip efficiency of the integrated plant reaches a maximum for a pressure ratio of about 5.2. A sensitivity analysis on the solar receiver temperature and turbomachinery polytropic efficiency and maximum allowable temperatures was also conducted. Finally, a feasible design for the PTES-CSP system characterized by an exergetic roundtrip efficiency of about 60% was proposed
Techno-economic comparison of different thermal energy storage technologies for medium-scale CSP plants
No full textThis paper is focused on the ongoing studies at the Ottana Solar Facility, a new experimental power plant located in Sardinia (Italy). The Ottana solar facility includes a 630 kWe CSP plant and a 400 kWe CPV plant. With reference to the CSP section, a solar field based on Fresnel technology with a net collecting area of about 8600 m2 is used to heat up a Heat Transfer Fluid (HTF) trough solar energy. A Turboden 6HR Special ORC unit is used for the thermal to electrical energy conversion by means of a regenerative Rankine cycle operated by an organic fluid. The system is also equipped with a two-tank direct Thermal Energy Storage (TES) system with a storage capacity of about 15 MWht. However, other possible configurations of the TES section are currently under investigation. In this regard, asingle-tank packed-bed TES system based on encapsulated phase-change materials (PCM) is proposed in this study as an alternative to the two-tank direct TES system currently in operation. A techno-economic analysis has been therefore carried out to compare the two TES configurations. A mathematical model has been developed under MATLAB environment for assessing the expected yearly performance of the plant. Finally, a preliminary economic analysis based on the calculation of the levelized cost of storage has been conducted. The results show that a decrease in the overall energy production occurs with the use of the single-tank TES system due to a general decrease of the HTF temperature feeding the ORC unit, as a consequent of the indirect heat exchange. On the other hand, the lower investment costs arising from the lower volume of oil and the use of a sole tank make the proposed TES alternative more attractive from an economic point of view
Performance evaluation of an integrated energy system for the production and use of renewable methanol via water electrolysis and CO2 hydrogenation
Full text linkAiming at the decarbonization of society, power-to-liquids processes can favour the exploitation of the excess of renewable energy, producing methanol or other chemicals (such as dimethyl ether) by reacting electrolytic hydrogen and recycled CO2 (captured from industrial and power plants or directly from air). Such a system could behave as: - an energy storage system, storing excess renewable energy as chemical energy in liquid fuels and converting it into electricity during lack of renewable energy, - a source of fuels and chemicals for a variety of applications in many industrial sectors. This work concerns the conceptual design and performance analysis of a small-scale integrated energy system for the production and use of methanol from renewable hydrogen and captured CO2. The main components of the system are: - a reversible high temperature and high efficiency solid oxide cell (RSOC) that can operate in charge (electrolyser, SOEC) and discharge (fuel cell, SOFC) mode to store and use electricity using methanol as energy storage medium, - a catalytic reactor for methanol synthesis via CO2 hydrogenation. A thermal energy storage (TES) system based on a phase change material (PCM) is also included. To predict performance of the main components and of the overall system, numerical simulation models were developed. Performance and efficiencies of each system component and of the overall system were evaluated through extensive mass and energy balances, considering two different configurations with and without TES integration. Performance indexes were calculated to analyse the goodness of introducing a TES. The global efficiency of the overall system increases from 30% to 35% when heat is recovered between sections via the TES system
Thermocline vs. two-tank direct thermal storage system for concentrating solar power plants: A comparative techno-economic assessment
Full text linkThis paper concerns the ongoing studies on a Concentrated Solar Power (CSP) plant in operation in Ottana (Italy), comprising a 629 kW organic Rankine cycle (ORC) unit fed by a linear Fresnel solar field. Hexamethyldisiloxane (MM) and “Therminol SP-I” are used respectively as ORC working fluid and heat transfer fluid in the solar receivers. A two-tank direct Thermal Energy Storage (TES) system is currently integrated in the CSP plant, serving as a direct interface between solar field and ORC. With the view of improving the solar facility, two alternative TES configurations were proposed in this study: a one-tank packed-bed TES system using silica as solid storage media and another similar one including encapsulated phase-change material (molten salt). Comprehensive mathematical models were developed for simulating daily behaviour as well as for assessing yearly performance of the various TES technologies. Furthermore, a preliminary economic analysis was carried out. Results showed poorer response of the one-tank TES system to large fluctuations in the ORC inlet fluid temperature, leading to reduction in the mean ORC efficiency (18.2% as against 19.7% obtained with the two-tank TES). Conversely, higher energy storage density and lower thermal losses were obtained adopting the one-tank TES, resulting in about 5% more annual solar energy yield. Invariably, equivalent annual ORC energy production of 0.92 GWh/year was obtained for the three TES configurations. Additionally, adopting a one-tank TES system meant that the purchase costs of a second tank and its storage medium (thermal oil) could be saved, resulting in investment costs about 45% lower and, ultimately, levelized cost of storage about 48% lower than what obtains in the two-tank TES system
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
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