1,720,960 research outputs found
Modeling and Sizing of a MW Solar DSG plant
Full text linkAbstractDirect Steam Generation (DSG) Concentrated Solar technology, based on Linear Fresnel Reflectors (LFR) and aimed at supplying saturated steam to industrial processes, is a promising application; nevertheless, nowadays few case studies and very few installations have been developed. A methodology for the design optimization of a MW solar DSG plant is presented in this article and applied to a real case study of a Brazilian tire manufacturing facility. A steady-state model, with spatial discretization of the ordinary equations, allows characterizing the physical phenomena such as pressure drop and heat transfer, and therefore to determine the pressure and specific enthalpy trend along the recirculation loop. For each receiver tube of the solar collectors, the occurring single or two-phase flow pattern is calculated based on specific empirical equations developed for evaporation in horizontal tubes. Two reference operating conditions have been identified for the present case study, at which the optimal field layout results to be a series connection of all the collectors, and the optimal nominal flow rate to avoid possible harmful operating conditions for the absorber tubes is 1.0kg/s
Solar Thermal Plant Integration into an Industrial Process
Full text linkAbstractThe present abstract summarizes the main analysis and design steps made for the integration of a solar thermal plant of one thousand square meters into the dyeing process of Benetton industrial facility in Tunisia. The analysis of the actual process load is done by a static model based on assumed energy and water consumptions and the real performance of the heat recovery system. The methodology to build the simplified model and its validation by monitored data will be presented. The results show the optimization potential of the heat recovery system and the temperature constraints for a good integration of the solar plant.This study presents some choices to reach an optimized integration of the solar plant and the sizing of the main components. The main design alternatives are evaluated in this article based on dynamic simulations and personal experience
A Continuous Commissioning Analysis and its Application to a New Installed Solar Driven DEC System Coupled with Heat Pump
Full text linkAbstractThe aim of this paper is to define and implement a continuous commissioning methodology that can be effectively applied to a solar driven desiccant and evaporative cooling (DEC) system. The objective is to assess the energy performance of the system's components and identify possible operation faults. The methodology consists in the breakdown and analysis of the DEC into sub-systems; for each of them a simplified dynamic mathematical model based on experimental data has been developed. A possible fault is detected when the difference between the theoretical and measured performances is higher than the accuracy of the methodology. The proposed methodology has been successfully implemented for a hybrid solar DEC system comprising a non-conventional DEC air-handling unit, a solar thermal system and an electrical heat pump.The results of the methodology's application to the first experimental data of summer 2014lead to the following conclusions: the solar sub-system operated as expected whereas the heat pump and the desiccant rotor did not. In particular, the electrical heat pump has a higher cooling capacity than the one predicted at partial load but with a similar COP value, this deviation is mainly due to the assumed partial load performance coefficient. The desiccant rotor presents a much lower performance than the one expected. However, the rotor inefficiency is difficult to highlight due to the high measurement uncertainties on the air side
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
Modellazione di un impianto solare per la generazione diretta di vapore e ottimizzazione della strategia di controllo
Full text linkLAUREA MAGISTRALEL’obiettivo di questo lavoro consiste nello studio di un impianto solare a concentrazione per la generazione diretta di vapore con collettori lineari di tipo Fresnel per la produzione di calore di processo a media temperatura per un’industria brasiliana. Due approcci sono stati usati per identificare le condizioni di funzionamento in condizioni nominali e transitorie. La modellazione stazionaria, con una discretizzazione spaziale delle equazioni ordinarie, permette di caratterizzare i fenomeni fisici come le perdite di carico lineari e scambio termico e quindi determinare la distribuzione di temperatura e pressione lungo l’assorbitore solare. Inoltre, con questo modello si riesce a calcolare il tipo di flow pattern esistente all’interno dei collettori in cui si forma vapore. Lo studio del flow pattern è cruciale per evitare possibili condizioni sfavorevoli all’interno dell’assorbitore che permetterà di allungare la vita utile del sistema. Dato che questo parametro è difficilmente misurabile, servono modelli per individuarlo. Questo primo approccio è necessario nella fase di dimensionamento e di verifica delle diverse condizioni di funzionamento. Per quanto riguarda l’analisi dei transitori è stato sviluppato un modello dinamico dove viene calcolata la variazione del livello di liquido, la pressione del drum (serbatoio di acqua liquida-vapore) e la portata all’interno dell’assorbitore per determinate condizioni operative ritenute rappresentative. Questo modello ha permesso di identificare un’elevata variazione di tali grandezze durante le fasi di partenza e spegnimento dell’impianto. Questa variazione è dovuta ai cambiamenti della distribuzione di vapore all’interno del sistema e deve essere controllata. Il modello dinamico si basa sullo sviluppo dei bilanci massico ed energetico sia dei sottosistemi (drum e assorbitore), sia del sistema complessivo. Infine, l’ottimizzazione della strategia di controllo ha lo scopo di limitare la variazione di pressione all’interno del drum e in un secondo tempo controllare la variazione del livello nel drum per minimizzarne il volume.The purpose of this work is the study of a Direct Steam Generation (DSG) Concentrated Solar Plant with Linear Fresnel Reflectors for medium temperature process heat production for a Brazilian industry. Two approaches are used to identify the operation conditions in nominal and transient conditions. The steady-state modeling, with a spatial discretization of the ordinary equations, allows to characterize the physical phenomena as pressure drop, heat transfer and, therefore, to determine the pressure and temperature distribution along the solar absorber. Also, with this model it’s possible to determine the flow pattern in each collector where steam is generated. The absorber flow pattern study is crucial to avoid possible adverse conditions of the absorber and will help to extend the life of the plant. Since it is quiet complex to measure it, a model has been developed. This first approach is necessary in the phase of sizing and verification of the different operation conditions. Regarding transient analysis, a dynamic model has been developed where parameters as absorber flow; drum (steam-liquid reservoir) pressure and liquid volume trends are calculated for certain representative days. This dynamic model shows large variations of these parameters during the start-up and shutdown. This variation is due to changes of the steam distribution inside the system and has to be controlled. The dynamic model is based on mass and energy balances of the sub-systems (drum and absorber) and the total system. Finally, the optimization of the control strategy has the purpose of limiting the pressure variation inside the drum and, in a second time, controlling the liquid drum level to minimize the necessary drum volume
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
Elaborazione di una procedura di continuous commissioning ed applicazione ad un impianto solar dec
Full text linkLAUREA MAGISTRALEIl presente lavoro di Tesi ha come scopo la definizione di una metodologia di Continuous Commissioning e la sua applicazione ad un sistema di climatizzazione DEC (Dessiccant Evaporative Cooling) assistito da energia solare e accoppiato a una pompa di calore elettrica. L’obiettivo dell’analisi consiste nel monitoraggio delle prestazioni dell’impianto a due livelli di dettaglio differenti, attraverso il confronto tra comportamento effettivamente registrato attraverso la lettura dei dati di misura acquisiti e la condizione di riferimento definita come situazione di idealità.
La prima parte, definita Commissioning specifico, consiste nell’analisi prestazionale dei principali sottosistemi componenti l’impianto (solare termico, pompa di calore, rotore), per i quali sono stati implementati modelli matematici dinamici. Tale indagine porta ad osservare che il sistema solare termico approssima in maniera soddisfacente il funzionamento ideale, mentre pompa di calore e rotore essiccante si discostano sensibilmente da quanto atteso.
Non è tuttavia possibile concludere che tali scostamenti siano dovuti ad effettive problematiche riguardanti i componenti stessi, in quanto il responso del rotore è sempre compreso all’interno dell’intervallo di incertezza che caratterizza la metodologia, mentre quello della pompa di calore è probabilmente affetto da un’incompleta valutazione delle prestazioni ai carichi parziali. Tuttavia, le tendenze prestazionali ottenute permettono di poter monitorare il decadimento delle performance dei componenti nel tempo.
La seconda parte, definita Commissioning generale, si pone il fine di analizzare le performance globali dell’impianto, stimando in maniera semplificata i consumi attesi a parità di condizioni al contorno. L’analisi porta inoltre alla stima dell’effetto del funzionamento non ottimale dei sottosistemi valutati in fase di Commissioning specifico sull’intero sistema. Il responso finale mostra che in linea di massima le prestazioni del sistema rientrano nell’intervallo di accettabilità definito, fatta eccezione per alcuni giorni in cui l’analisi ha permesso di rilevare la presenza di malfunzionamenti.The aim of the present Thesis work is the definition of a Continuous Commissioning methodology and its application to a solar driven Dessiccant Evaporative Cooling (DEC) system coupled with an electrical heat pump (EHP). The analysis consists in a two levels monitoring procedure. The real behavior of the system is compared with the theoretical one, with the aim of assess if the difference is out the uncertainty bounds.
The Specific Commissioning procedure is implemented in order to evaluate the performance of the three principal subsystems (solar thermal system, electrical heat pump and desiccant rotor) through dynamic mathematical models. The results show that the solar thermal system operated as expected, the heat pump has different partial load behavior from the predicted, and the desiccant rotor presents a much lower performance than the ideal condition. However, the rotor inefficiency is included in the uncertainty range, and for the heat pump a specific analysis of the partial load conditions has to be implemented. The achieved results also allow the opportunity of the performance decay evaluation of the analyzed subsystems during the future operation.
The General Commissioning procedure has the aim to estimate the overall consumptions according to external weather conditions. A simplified energetic model of the whole plant allowed the comparison between real and expected behavior, and quantified the impact on the whole plant consumption of the underperformance subsystems. The value of the calculated indices suggests that the system performances are generally in agreement with the hypothesis, taking into account the uncertainty range of the methodology. During a non-optimal operation period it was possible to test the procedure’s detection capacities of plant faults
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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