1,721,026 research outputs found
Flow force reduction in hydraulic proportional directional valves by means of the spool geometry optimization
No full textSperimentazione e sviluppo di impianti di refrigerazione ecosostenibili
No full textIn questo lavoro è stato studiato un ciclo Joule-Brayton inverso ad aria, con una variante al fine di realizzare un impianto di refrigerazione mediante l’utilizzo di un turbogruppo di derivazione automobilistica. Inizialmente, è stato realizzato e testato presso il Laboratorio di Macchine del Politecnico di Bari un impianto sperimentale al fine di analizzare le problematiche principali che limitano le prestazioni del ciclo ad aria. Si tratta di un impianto a circuito aperto con una compressione bistadio interrefrigerata, senza scambiatore di recupero. Le misure effettuate hanno rivelato performance inadeguate, sia in termini di efficienza sia di temperatura minima raggiungibile, causate principalmente dal basso rendimento della turbina nelle condizioni di utilizzo rispetto a quelle per cui sono progettati i turbogruppi automobilistici. E’ stato quindi proposto un nuovo layout dell’impianto, basato su due criteri progettuali. Il primo prevede una condizione di accoppiamento ottimale tra il turbogruppo e l’impianto di refrigerazione; il secondo, invece, l’utilizzo di gruppi di sovralimentazione più grandi, in grado di raggiungere efficienze maggiori. In accordo con questi due criteri progettuali è stato simulato al calcolatore un ciclo recuperativo, che lavora in gran parte in depressione, rispetto alla pressione atmosferica, in modo da avere portate volumetriche circolanti più grandi e poter utilizzare macchine di più elevata efficienza. I risultati ottenuti mostrano che il nuovo impianto è in grado di fornire aria a temperatura relativamente bassa (-60°C ed oltre), rendendolo adatto anche per applicazioni di congelamento. Inoltre, la presenza del recuperatore rende la temperatura dell’aria in uscita dalla turbina praticamente indipendente dalla temperatura ambiente, per cui il ciclo proposto potrebbe operare adeguatamente anche in ambienti molto caldi
Development and Testing of Sustainable Refrigeration Plants
No full textAlthough Ozone Depleting Substances (ODS) were banned with the Montreal Protocol in 1987, current refrigeration plants can not be considered sustainable for the environment. ODS have been in fact substituted by gases with high Global Warming Potential (GWP). Among many alternatives, inverse Joule Brayton air cycle had been already implemented and tested for refrigeration purposes. In the open cycles described in the available literature, the operating fluid (air) is firstly compressed by a bootstrap (volumetric) compressor and then processed by a second (centrifugal) compressor and cooled; then, it is expanded in a turbine which drives the centrifugal compressor and discharges a cold flow which can be used (directly or indirectly) for refrigeration purposes. In this work, an inverse Joule Brayton air cycle has been studied with the employment of turbocharger units. Experimental tests have been performed in order to reproduce the state-of-the-art with a small automotive turbocharger unit. Measurements show Coefficient Of Performance (COP) smaller than unit together with minimum turbine exit temperature equal to -10°C. This is due to low components efficiency: the analysis of turbine and turbocompressor maps highlights a non-optimal coupling between them. Secondly, basing on these considerations, two new air cycle layouts are proposed and analyzed. Calculations performed by means of a thermodynamic model show that higher COP and lower cycle minimum temperature can be achieved with the proposed new cycles by means of better turbine and turbocompressor matching and bigger turbocharger units with higher components efficiency
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
Parametric Study of an Innovative Counter-Flow Heat Exchanger
No full textAn innovative Counter-Flow Sand Heat Exchanger (CFS-HX) is proposed, which makes use of very small solid particles as intermediate medium to perform heat transfer between two gas flows at different temperature. The potential of the CFS-HX was already demonstrated by the authors, both theoretically and experimentally. In this work, a parametric study has been employed in order to explore the capabilities of the proposed heat exchanger. A 1D model (validated by experiments) has been extensively used to perform sensitivity analyses with respect to the major design parameters, i.e.: specific heats, gas and sand densities, particle diameter, prescribed efficiency. Pipe length to obtain a prescribed heat exchanger efficiency has been calculated for a large number of configurations and results have been compared with a baseline case. The proposed computations show that a high efficient heat exchange can be obtained with relatively short pipes and with negligible pressure drop.</jats:p
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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