1,720,967 research outputs found
Analysis of a helical coil once-through molten salt steam generator: Experimental results and heat transfer evaluation
No full textA molten salt helical coil steam generator is an alternative to kettle- or drum-type evaporators which are currently used in commercial-scale solar thermal power plants. A 300 kW prototype was tested during the OPTS project at ENEA. The experimental results presented in this paper have been used to validate a detailed heat transfer analysis of the whole system. The heat transfer analysis deals with the study of both the overall heat transfer coefficient and the shell-side heat transfer coefficient. Due to the specific features of this type of system, no correlations were available in the literature. A new numerical model to predict the performance of large-scale systems is also presented. © 2016 Author(s)
Thermal characterization of a stratifying molten salts storage tank with integrated steam generator in real operating conditions
No full textIn the last years, ENEA proposed a new concept of thermocline thermal energy storage system based on a single storage tank containing a binary mixture of molten salts (working both as heat storage medium and heat transfer fluid in the solar field), and a once-through steam generator integrated in it. This component works like a steam generator of a fast nuclear reactor, exploiting the temperature difference of the mixture of salts stratified in the tank between a hot layer (550°C) and a cold one (290°C) to produce superheated steam. In the present paper, are shown the experimental tests carried out to characterize and to assess the performance of the temperature stratification of the molten salts in such a system. The tests have been carried out with the storage tank of the PCS Facility, at Casaccia Research Centre of ENEA (Rome, Italy), and a 300kWth shell-and-tube once-through steam generator integrated in it. The experimental activities verified that the thermal stratification conditions of the molten salts contained in the storage tank are stable over time, and the integrated once-through steam generator is the active element that triggers and maintains over time the stratification of the molten salts. © 2018 Author(s)
Progettazione e realizzazione di uno scambiatore di calore prototipico per reattori refrigerati a sodio con circuito intermedio a sali fusi
Full text linkÈ stata progettata e messa a punto una Sezione di Prova dedicata a una campagna sperimentale volta a definire le caratteristiche di un sistema innovativo, a sicurezza intrinseca in quanto privo di elementi attivi, per la rimozione del calore di decadimento della piscina di stoccaggio elementi esauriti di una centrale nucleare. La Sezione di prova, consistente in uno scarnbiatore di calore costituito da un tubo alettato con circolazione naturale dei fluidi di scambio del calore, verrà installata sull'Impianto sperimentale MOSE sito presso il CR Casaccia dell'ENEA
Experimental tests about the cooling/freezing of the molten salts in the receiver tubes of a solar power plant with parabolic trough
No full textIn 2003 ENEA realized the PCS experimental Facility at Casaccia Research Centre (Rome, Italy), in order to test in real operating conditions the components of a parabolic trough solar plant, and to evaluate the technical feasibility of using the solar molten salts mixture (60% NaNO3, 40% KNO3, melting point 220÷240°C) in such a type of plant. ENEA also had the need to assess the behaviour of the solar receiver tubes during abnormal operating situations (wrong operation, pump block, power failure, etc.), when a block of the circulation of the molten salts may occur and cause the cooling or, worse, the freezing of the salts mixture inside the pipes. Some experimental tests have been performed, aimed to examine what happens in such a cases. In fact, without quick maneuvers to restart the circulation of the molten salts or to readily empty the receiver tubes, the molten salts contained in them may cool down to temperatures near/below the solidification. In this report are shown the results of the experimental tests carried out on the receiver tubes of the PCS Facility by cooling the process fluid down to temperatures near or below its freezing point. The tests show that the solidification of the salts does not damage the components of the plant but it is manageable and reversible, provided you apply the correct procedures. © 2017 Author(s)
CFD model of a molten salt tank with integrated steam generator
No full textFor each solar technology the dispatchable CSP plant scheme that maximizes the solar to electrical energy conversion and minimizes the costs associated to such transformation is searched. In recent years double tank TES systems are evolving towards more simple configurations of a single tank [1], [2], [3], also known as thermocline tank TES systems and, even going beyond, there are already thermocline tanks in process of development where the steam generator (SG) is integrated into the storage tank (European project OPTS). A prototype with integrated SG has been erected for testing purpose in the Casaccia Research Centre of ENEA (Italy) [4]. The model presented in this paper reproduces the experimental data of such prototype using the CFD commercial code STAR-CCM + [5]. Unlike very few published until now [6]. The simulated system account for molten salts behavior, not only for the bulk molten salts, but also for the circulation of the molten salts inside the SG (with three steam coils). The molten salts move by induced natural convection and the steam temperatures and pressures are up to ∼500° C/40bar. Temperature gauges situated in the bulk and the molten salts mass flow inside the SG are the main variables considered for validating the model. From the numerical point of view is a transient simulation and the model is 2D-axisymmetric. The required features of the system mesh and the physical models used are presented in this work. © 2013 The Authors
An Innovative Concept of a Thermal Energy Storage System Based on a Single Tank Configuration Using Stratifying Molten Salts as both Heat Storage Medium and Heat Transfer Fluid, and with an Integrated Steam Generator
No full textAbstractThe proposed innovative thermal energy storage system is based on a single tank containing a mixture of nitrate salts (60% NaNO3 and 40% KNO3 in weight; this mixture gradually changes from solid to liquid in the temperature range between about 220°C and 240°C, becoming completely melted above this temperature), with an integrated steam generator directly contained inside it. The system is operated exploiting the thermal stratification of the salts mixture in the temperature range between 550°C (hot temperature) and 290°C (cold temperature). The experimental work conducted at ENEA has revealed that the thermal stratification of the molten salts mixture can be maintained quite constant for several hours and the presence of the integrated steam generator actively guarantees and maintains the stratification during the operation time, avoiding mixing of the stratified layers. The single-tank system with stratification of the molten salts and an integrated steam generator is an important improvement in terms of efficiency, reliability and cost reduction, with respect to the two-tank thermal energy storage system. This report has the aim of giving an overview of this new technology but, given the fact that the experimental activities are still ongoing, the description of the system remains at a qualitative level. The complete set of experimental results will be presented in the future when the Projects that are framework of this research will have been completed
Power production of an ORC system using a stratified molten salt as thermal energy storage integrated in a CSP plant
No full textThe use of Organic Ranking Cycle (ORC) systems to produce electrical energy in Concentrating Solar Power (CSP) plants has been significantly increasing over the recent years, mainly for small size plants [1-2]. The project ORC-PLUS, in the frame of Horizon2020, aims to deepen this aspect for an existing CSP plant located in a desert area at Ben Guerir in Morocco and using linear Fresnel collectors as well as thermal oil as heat transfer fluid (HTF). This plant foresees mainly two different operative modes: during daytime with sufficient Direct Normal Irradiance (DNI) an Organic Rankine Cycle (ORC) system is directly coupled to a 7 loops solar field; after sunset the ORC is fed by a thermal storage coupled to an additional solar field consisting of 3 loops. In the same context the performances of a stratified molten salt as thermal energy storage (TES) are deepened at ENEA CR Casaccia in Italy. Aim of this paper is the analysis of the power production of the 1 MWe ORC system present in the plant, under different operating conditions using a proper computing model
Experimental Validation of the Innovative Thermal Energy Storage Based on an Integrated System “Storage Tank/Steam Generator”
No full textAbstractIn the past years, an innovative thermal energy storage system at high temperature (up to 550̊C) for CSP plants was proposed by ENEA and Ansaldo Nucleare: a single storage tank integrated with a steam generator immersed in the heat storage medium. The idea is based on the exploitation of the thermophysical characteristics of the heat storage medium (a binary mixture of salts of NaNO3 at 60% and KNO3 at 40%) in order to maintain over time, in the single tank, a thermal stratification of the fluid. The thermal stratification is able to trigger, in the immersed steam generator, the natural circulation, shell side and downwards, of the hot molten salt cooled down by the water that flows upwards tube side, thus heating up and producing superheated steam. The advantages of such a system are: - efficient performances; - simple implementation; - compactness: - modularity; - and, overall, contained costs: only one storage tank instead of the two tanks and only one heat exchanger instead of the three exchangers of the classic configuration; reduced quantity of salt; minimization of piping, valves and other components. The technical feasibility of the proposed system, together with the stability over time of the stratification in temperature of the storage medium, have been already verified and assessed. This report has the aim of presenting the experimental results obtained by ENEA in the Casaccia Research Centre (Rome, Italy), with a small scale test section consisting of a 300 kWth steam generator inserted in a 8 m3 storage tank with molten salt at high temperature. The reported results relate to the behaviour of the system in steady state conditions, and show its promising performances
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
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