1,721,176 research outputs found
Dense Gas Thermodynamic Properties of Single and Multicomponent Fluids for Fluid Dynamics Simulations
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Molecular interpretation of nonclassical gas dynamics of dense vapors under the van der Waals model
Full text linkThe van der Waals polytropic gas model is used to investigate the role of attractive and repulsive intermolecular forces and the influence of molecular complexity on the possible nonclassical gas dynamic behavior of vapors near the liquid-vapor saturation curve. The decrease of the sound speed upon isothermal compression is due to the well-known action of the van der Waals attractive forces and this effect is shown here to be comparatively larger for more complex molecules with a large number of active vibrational modes; for these fluids isentropic flows are in fact almost isothermal. Contributions to the speed of sound resulting from intermolecular forces and the role of molecular complexity are analyzed in details for both isothermal and isentropic transformations. Results of the exact solution to the problem of a finite pressure perturbation traveling in a still fluid are presented in three exemplary cases: ideal gas, dense gas and nonclassical gas behavior. A classification scheme of fluids based on the possibility of exhibiting different gas dynamic behaviors is also proposed.Process and EnergyMechanical, Maritime and Materials Engineerin
Thermal energy storage for solar-powered organic Rankine cycle engines
No full textThe feasibility of energy storage is of paramount importance for solar power systems, to the point that it can be the technology enabler.
Regarding concentrated solar power (CSP) systems, the implementation of thermal energy storage (TES) is arguably a key advantage over systems based on photovoltaic (PV) technologies. The interest for highly efficient and modular CSP plants of small to medium capacity (5 kWE–5 MWE) is growing: organic Rankine cycle (ORC) power systems stand out in terms of efficiency, reliability and cost-effectiveness in such power-range. In this paper a thorough investigation on thermal storage systems tailored to high-temperature (300 C)ORCpower plants is addressed first, stemming from the observation that the direct storage of the ORC working fluid is effective thanks to its favourable thermodynamic properties. The concept of complete flashing cycle (CFC) is then introduced as a mean of achieving an unmatched system layout simplification, while preserving conversion efficiency. This is a new variant of the Rankine cycle, whereby the vapour is produced by throttling the organic working fluid from liquid to saturated vapour conditions. The presentation and discussion of a case study follows: a 100 kWECFCsystem with direct thermal energy storage, coupled with state-of-the-art parabolic trough collectors. The proposed turbogenerator
achieves an estimated 25% efficiency, which corresponds to a value of 18% in design conditions for the complete system. Considering
siloxanes as working fluids, the estimated values of storage density are around 10 kW eh=m3 storage
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
Dynamic simulation of a biomass-fired power plant: a comparison between causal and a-causal modelling
No full textAPPARECCHIATURE PER PROVE DI STABILITA' TERMICA SU FLUIDI ORGANICI PER CICLI A FLUIDO BIFASE
No full textLe apparecchiature in uso da alcuni anni presso il Politecnico di Milano e le procedure sperimentali per prove di stabilità termica sono state estesamnte modificate; la soglia di pirolisi dei fluidi viene evidenziata dalla misura della pressione isoterma in autoclavi termstatate, dal confronto della curva di tensione di vapore e dall'analisi gas-cromatografica del campione. L'affidabilità impiantistica e strumentale richieste hanno imposto la soluzione di problemi associati alla tenuta, ai disturbi introdotti dalle variazioni della temperatura ambiente, alla preparazione dei fluidi, nonché all'efficace rilevazione della curva di tensione di vapore
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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