1,720,974 research outputs found
Selected Papers from the 12th International Conference on Computational Heat and Mass Transfer (ICCHMT2019)
No full textExperimental and analytical evaluation of a gas-liquid energy storage (GLES) prototype
No full textIn this paper, a novel gas-liquid compressed air energy storage prototype, installed in the laboratory of DIAEE Department of Sapienza University of Rome, is studied. Similar to the Compressed-Air Energy Storage (CAES), the Gas-Liquid Energy Storage (GLES) technology is based on gas compression/expansion, where the liquid-piston compression and expansion are utilized. This paper reports on the experimental performance of the first GLES prototype and presents the results from a validated mathematical model. The results show that the proposed system has a high energy efficiency (indicated) over 90%, and then to achieve high values of round trip efficiency (RTE), it is important to improve and optimize the efficiency of the auxiliaries (Motor/Pump and Turbine/Generator). Two different Test, with two different speed of charging phase were done. From the results of the experimental measurements done with the prototype built in the laboratory of the DIAEE Department of Sapienza University of Rome, it can be seen that for slow compression the RTE of the system is around 72%, instead for the fast compression phase, the RTE is around 70%. A mathematical model was implemented and tested with the experimental measurements. From results it can be seen a good agreement between the experimental and numerical analysis, with a maximum error in the Test B (slow compression) equal to 2.5% and 1% respectively for charging and discharging phase. From the parametric analysis it can be seen that only the volume of the tank and the pressure ratio are needed to predict the round trip efficiency of the system.(c) 2021 Published by Elsevier Ltd
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
Energy analysis of a thermal system composed by a heat pump coupled with a PVT solar collector
No full textThe development of heat pump technology in the tertiary sector can lead to a reduction in greenhouse emissions and enhanced exploitation of renewable energy sources, including solar energy. The present paper investigates the potentiality of an energy system equipped with photovoltaic thermal (PV) hybrid solar collectors, a storage tanks for the heat source and a heat pump for the space heating of a small office located in three different European cities. The behaviour of the heat pump according to the heat taken from the photovoltaic panels and stored in the tank has been analysed. An energy analysis was performed according to the efficiency of the heat pump and then the thermodynamic parameters of the system were evaluated. The analytical model of each subsystem of the thermal plant was developed in Matlab where hourly simulation during the period of heating season were performed. Therefore, a comparison between the results obtained for Rome, Milan and Cracow provided the heating energy demand covering rate for each of the cities in different subsystem efficiency conditions. When thermal and electrical efficiency of PVT are set respectively to 0.6 and 0.15 and the efficiency of storage unit heat exchanger is considered equal to 0.9 the heating demand covered for Rome is 70%, for Milan is 62%, while for Cracow is 47%. Those values show a good potential for supporting heat-pump based PV-T heating systems
Numerical investigation of conjugate heat transfer from laminar wall jet flow over a shallow cavity
No full textIn this paper, numerical investigation of two-dimensional conjugate heat transfer of laminar wall jet flow over a shallow cavity heated from the bottom of the solid wall is carried out. The flow and conjugate heat transfer behaviors, isotherm contour in the cavity region, isotherm contour on the solid, interface temperature, local Nusselt number (local Nu), and average Nusselt number (average Nu) are investigated for various parameters, viz., Re, AR, Xu, and b. The momentum of the fluid is gradually reduced when the step length Xu is increased. It is noticed that the interface temperature value is decreased when b is increased. Near the trailing edge, the local Nu is decreased and near the leading edge, the local Nu is increased when AR is increased. It is noticed that the average Nu is increased when Re is increased on the cavity floor. The average Nusselt number values are compared with non-conjugate cases. It is observed that the average Nusselt number for non-conjugate is comparatively higher than that of conjugate cases
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
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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