Direct steam generation solar systems with screw expanders and parabolic trough collectors: Energetic assessment at part-load operating conditions

This paper explains a numerical optimization of a novel screw expander-based solar thermal electricity plant to evaluate the energetic benefits in specific case studies. In the proposed solar electricity generation system, which is based on the steam Rankine cycle, water is used as working fluid and storage, parabolic trough collectors as a thermal source and screw expander as power machine. Such solar system offers major advantages over conventional power plants adopting steam turbines: low operating pressures, good exploitation of low temperature heat sources, acceptable efficiency in energy conversion with steam-liquid mixtures and reduced size. Since screw expanders can operate at off-design working conditions in several situations when installed in direct steam generation solar plants, the chief purpose of the present study is to develop a thermodynamic model to analyse the energy performance of the planned solar power system when off-design operating conditions befall. To assess maximum efficiency of the whole power plant at part-load operating conditions, numerical optimization is then performed in a specific range of fluctuating evaporation temperatures under fixed condensation pressures. Keywords: Steam screw expander, Solar thermal power efficiency, Direct steam generation, Part-load behavior, Polytropic expansion phas

Combined use of volumetric expanders and Scheffler receivers to improve the efficiency of a novel direct steam solar power plant

This research proposes an innovative solar thermal plant able to generate mechanical power through an optimized system of heliostats with Scheffler-type solar receivers coupled with screw-type steam expanders. Scheffler receivers appear to perform better than parabolic trough collectors due to the high compactness of the focal receiver, which minimizes convective and radiative heat losses even at high vaporization temperatures. At the same time, steam screw expanders are volumetric machines that can be used to produce mechanical power with satisfactory efficiency also by admitting two-phase mixtures and with further advantages compared to steam turbines: low working fluid velocities, low operating pressures, and avoidance of overheating. This study establishes a mathematical model to assess the energetic advantages of the planned solar thermal power system by evaluating the solar-to-electricity efficiency for different off-design working conditions. For this purpose, a numerical model on the Scheffler receiver is initially investigated, thus assessing all the energy losses which affect the heat transfer phase. A thermodynamic model is then developed to evaluate the energy losses and performance of the screw expander under real working conditions. Finally, parametric optimization of the solar energy conversion is performed in a wide range of operating conditions by establishing thermodynamic formulations related to the whole solar electricity generation system. Water condensation pressure and vaporization temperature are so optimized with respect to global energy conversion efficiency which, under the best operating conditions achieved in this research, rises from 10.9% to 14.4% with increasing solar irradiation intensity. Hence, the combined use of screw expanders and Scheffler receivers for solar thermal power system application can be a promising technology with advantages over parabolic dish concentrators. Novelty statement: This research proposes an innovative direct steam solar power plant based on an SRC, with water utilized as both heat transfer and working fluid, equipped with Scheffler solar receivers as a thermal source and screw expanders as work-producing devices. Technical studies and energy assessments of this kind of SEGS at part-load operation do not exist in scientific literature; after reviewing the literature, it was determined that volumetric expanders have been rarely combined with Scheffler receivers for solar thermal power system application. In effect, combined use of screw expanders and Scheffler-type solar concentrator in a direct steam solar power system represents a completely new plant configuration; however, as a promising DSG solar system, at present numerical model of this new sort of SEGS is lacked in literature and the optimum operating conditions have yet to be defined. For this reason, the chief objective of this paper is to define a first parametric optimization of all thermodynamic variables involved to maximize global efficiency of the proposed solar thermal power generation system for ordinary working conditions

Analisi teorica e sperimentale di getti liquidi nebulizzati per processi di combustione stazionaria e per raffreddamento intensivo di superfici solide

Dottorato di ricerca in ingegneria dei sistemi termomeccanici. 7. ciclo. A.a. 1994-95Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Analisi e caratterizzazione sperimentale di spray per sistemi antincendio

Lo scopo del progetto svolto da questa unità di ricerca è capire in modo approfondito la fisica dei sitemi spray per antincendio quali water mist e sprinkler e fornire dati ottenuti sperimentalmente per poter supportare ed integrare la fase di simulazione numerica. Le misure saranno condotte su spray ad alts pressione e quindi fortemente nebulizzati quali water mist (100 bar) e bassa pressione quali gli sprinkler (10 bar).La fase sperimentale sarà condotta su ugelli hollow e full cone in assenza ed in presenza di sorgenti di calore. Le prove verranno condotte su ugelli singoli e non verranno quindi prese in considerazione eventuali interazione fra spray. Vengono usate diverse tecniche di misura. La caratterizzazione degli spray verrà portata avanti mediante il sistema PDA bidimensionale. Esso verrà adoperato insieme ad una termo camera ad infrarosso ad alta velocità in grado di evidenziare lo sviluppo nel tempo del campo termico anche in condizioni in stazionarie. Viene quindi sviluppata una metodologia di misura atta a determinare le caratteristiche di uno spray antincendio e a fornire le relative interazioni in ambienti sever