1,720,966 research outputs found
Accumulo termico ad alta temperatura per impianti solari termodinamici
No full textsi propone di analizzare il comportamento della sezione di accumulo termico di un impianto solare termodinamico che utilizza
un gas (CO2) come fluido termovettore e di valutarne le prestazioni mediante un modello matematico semplificato.
Il comportamento della sezione di accumulo termico viene analizzato, considerando lo scambio termico tra il fluido
termovettore ad alta temperatura e il materiale solido ad alta capacità termica utilizzato per lo stoccaggio dell'energia durante i
periodi di elevata radiazione solare. La fase di accumulo e quella successiva di restituzione dell’energia termica viene studiata
mediante un modello matematico di tipo non stazionario a due fasi basato sul modello di Schumann applicato ad uno strato del
serbatoio di spessore infinitesimo. Durante la fase di carica, all’interno del serbatoio si sviluppa un profilo di temperatura
(termoclino) che unisce la parte superiore del serbatoio che si trova a temperatura più elevata con quella inferiore a temperatura
più bassa.
Dopo aver messo in evidenza l’influenza dei vari parametri geometrici sulle prestazioni del sistema di accumulo, lo studio
si è concentrato sulla risoluzione di alcune criticità legate alla ripetizione ciclica delle fasi di carica e scarica dell'accumulatore
che comporta la presenza di isteresi termica. Vengono pertanto proposte alcune soluzioni per rendere più efficiente la gestione
dell’accumulatore e dell’utilizzazione dell’energia termica tramite la modifica dei vincoli sulla temperatura minima e massima
del fluido in uscita dall’accumulatore durante le fasi di carica e scarica. I risultati mostrano un considerevole aumento delle
capacità di accumulo e di efficienza del sistema e la possibilità di ridurre notevolmente gli effetti dell’isteresi termica durante il
processo ciclico di carica e scarica del serbatoio al crescere della temperatura minima e al diminuire di quella massima.
Viene inoltre simulato il comportamento del sistema di accumulo per una condizione tipica di funzionamento reale ovvero
con l’intensità della radiazione solare variabile durante l’arco di una giornata tipicamente estiva
Il progetto ESTATE-Lab: un impianto solare termodinamico operante con fluidi termovettori gassosi ad alta temperatura
No full textIn this work is presented the project named ESTATE-Lab, sponsored by CRS4, RTM Spa, SAPIO Srl, Sardegna Ricerche
and the departments of Mechanical Engineering and Electrical and Electronic Engineering of the University of Cagliari and
funded by MIUR through the law L297/99. The objective of the project ESTATE-Lab is the building of a "public-private
laboratory for the development of technologies for solar thermal energy at high temperature."
The project focuses on some research and development activities aimed to "demonstrate the feasibility of efficient
production, clean and competitive electricity from solar energy, through the thermodynamic management at high temperature
(550 °C) of solar energy which is collected, concentrated and stored.". The lab will allow to conduct research and development
activities on solar thermodynamic exploring innovative solutions than the commonly used technologies. In particular, the
project ESTATE-Lab consists of three lines of solar collectors of parabolic trough type where the carbon dioxide is used as
operating fluid.
The use of a working fluid in gaseous state will allow to achieve higher temperatures (550 °C) than those normally taken in
the thermodynamic solar plants built to date. Moreover, in the project ESTATE-Lab, is present a section of accumulation of
thermal energy which is based on heat exchange between carbon dioxide and solid materials at high heat capacity. This mode
of storage allows the management of heat accumulated by means of the evolution of temperature profile (thermocline).
In this work, in addition to the description of the laboratory, are also presented the models of simulation used to assess the
performance of the plant and the results of comparative studies that led to the choice of carbon dioxide as working fluid.
In addition, also the simulation results of the section of heat accumulation in different conditions of solar radiation are
reported
Numerical investigation of a packed bed thermal energy storage system with different heat transfer fluids
No full textThis paper presents the results of a numerical investigation on the transient behaviour of a packed bed thermal
storage unit using different fluids: oil, molten salt and air. The storage material consists of loosely spherical particles
of alumina packed in a reservoir wherein the heat transport fluid flows from the top to the bottom in the charging
phase, and in the opposite way in the discharging phase. The process of charge/discharge of the storage system gives
rise to a typical temperature distribution along the flow direction defined "thermocline". The main objective of this
work is to analyze the temperature distribution along the storage system and the formation of the thermocline for
repetitive consecutive cycles, evaluating the progressive reduction of the stored energy in the solid material for
every new cycle. The numerical investigation is based on a two-phase one-dimensional modified Schumann model,
where thermodynamic properties of the fluid are temperature dependent
Analisi numerico-sperimentale di un sistema per l’accumulo di energia termica con materiale solido
No full textIn questo lavoro viene presentato un set-up sperimentale per lo studio dell’accumulo di energia termica mediante materiale solido inerte utilizzante aria come fluido termovettore. Le indagini sperimentali hanno mostrato come il profilo di temperatura all’interno del serbatoio di accumulo si sviluppi con la formazione di un termoclino. I risultati ottenuti hanno consentito di validare il modello matematico sviluppato per prevedere il comportamento di questa tipologia di sistemi di accumulo
Experimental investigation of a packed bed thermal energy storage system
Full text linkIn this work experimental investigations on a thermal energy storage system with a solid material as storage media and air as heat transfer fluid will be presented. The experimental test rig, installed at the DIMCM of the University of Cagliari, consists of a carbon steel tank filled with freely poured alumina beads that allows investigations of heat transfer phenomena in packed beds. The aim of this work is to show the influence of the operating conditions and physical parameters on thermocline formation and, in particular, the thermal behaviour of the thermal energy storage for repeated charging and discharging cycles. Better charging efficiency is obtained for lower values of mass flow rate and maximum air temperature and for increasing aspect ratio. A decreasing influence of the metal wall with continuous operation is also highlighted. In conclusion, the analysis focuses on the thermal hysteresis phenomenon, which causes degradation of the thermocline and the reduction of the energy that can be stored by the accumulator as the repeated number of cycles increases
A comparison between CFD simulation and experimental investigation of a packed-bed thermal energy storage system
No full textThis work presents the comparison between CFD and experimental results obtained on a sensible thermal energy storage system based on alumina beads freely poured into a carbon steel tank. Experimental investigations of charging and discharging phases were carried out at a constant mass flow rate using air as heat transfer fluid. The experimental set-up was instrumented with several thermocouples to detect axial and radial temperature distribution as well as reservoir wall temperature. The experimental results were compared with those obtained from CFD simulations carried out with the FLUENT software. The computational domain consists of an axisymmetric tank of cylindrical shape filled with a porous bed coupled with the wall. The governing equations are solved for incompressible turbulent flow and fully developed forced convection, based on the two-phase transient model equation (LTNE-local thermal non-equilibrium) to calculate the temperature of fluid and solid phases. The porosity of the bed is considered variable in the radial direction, while the thermodynamic properties of both phases are temperature-dependent. The influence of the thermal dispersion within the porous bed, as well as the effective conductivity between the beads was considered. The heat transfer coefficient was calculated according to correlation for forced convection within porous media. Numerical results show a good agreement with experimental ones if thermal properties are considered temperature-dependent and the experimental temperature profile at the inlet of the bed is applied as a boundary condition in the simulations
Operating performance of a Joule-Brayton pumped thermal energy storage system integrated with a concentrated solar power plant
Full text linkThe expected performance of an innovative Pumped Thermal Energy Storage (PTES) system based on a closed-loop Brayton-Joule cycle and integrated with a Concentrated Solar Power (CSP) plant are analysed in this study. The integrated PTES–CSP plant includes five machines (two compressors and three turbines), a central receiver tower system, three water coolers and three Thermal Energy Storage (TES) tanks, while argon and granite pebbles are chosen as working fluid and storage media, respectively. A sizing of the main components of the integrated plant has been firstly carried out for the design of an integrated PTES-CSP plant with a nominal net power of 5 MW and a nominal storage capacity of 6 equivalent hours of operation. Specific mathematical models have been developed in MATLAB-Simulink to simulate the PTES and CSP subsystem in different operating conditions, and to evaluate the thermocline profile evolution within the three storage tanks during/charging and discharging processes. A control strategy has finally been developed to determine the operating modes of the plant based on the grid service request, the solar availability, and the TES levels. The performance of the system during a summer and a winter day have been analysed considering the integration of the PTES subsystem in the Italian energy market for arbitrage. Results have demonstrated the technical feasibility of the hybridization of a PTES system with a CSP plant and the ability of the integrated system to participate to energy arbitrage, although a lower exergy roundtrip efficiency (about 54 %) has been observed with respect to the sole PTES system (about 60 %)
Concentrating solar collectors integrated with low CO2 emissions ultra supercritical power plants
No full textThis paper focuses on the evaluation of the potential benefits arising from the integration of concentrating solar systems with coal-based Ultra Supercritical (USC) power plants with post-Combustion CO 2 Capture (PCC). In this study, the USC-PCC plant was integrated with a concentrating solar field with or without a thermal energy storage section. Different collector technologies (parabolic trough and linear Fresnel) and heat transfer fluids (direct steam generation and molten salts) were analyzed and compared. The performance of both solar field and power plant were evaluated by means of specifically developed models, by using data sets of a typical meteorological year for two sites in Italy and Morocco. A preliminary cost analysis was finally carried out
Nanofluids in Thermal Energy Storage Systems: A Comprehensive Review
Full text linkNanofluids, which consist of nanosized particles dispersed in a base fluid, represent a promising solution to improve the performance of thermal energy storage systems. This review offers a comprehensive overview of nanofluids and their applications in thermal energy storage systems, discussing their thermal properties, heat transfer mechanisms, synthesis techniques, and application in latent heat storage systems. Various types of nanofluids are examined, including metal oxide, carbon-based, and metallic nanofluids, highlighting their effects on thermal conductivity, latent heat and the phase change temperature. A review of experimental and numerical studies showcases the performance of thermal energy storage systems incorporating nanofluids and the factors influencing their thermophysical characteristics and energy storage capacity. Finally, the key findings of current research are summarized, as well as the challenges and the potential future directions in nanofluid-based thermal energy storage systems research, emphasizing the need to optimize nanoparticle concentration and long-term durability
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