1,720,966 research outputs found
Parallel connected natural circulation loops using different working fluids: experimental results
No full textNatural Circulation Loops (NCLs) are closed-loop systems that transport heat from a source to a heat sink without a pump, relying on free convection of the working fluid. Previous research has focused on the stability and influence of different operative parameters on NCLs. This experimental study investigates the thermo- hydraulic performance of three parallel-connected NCLs with small inner diameters using three different working fluids: deionized water, glycol aqueous solution (50+50% wt), and FC-43 dielectric fluid. This study examines the steady-state behaviour of the NCLs at various heat sink temperatures and heat powers. The results indicate that the common one-dimensional model for a single loop's steady-state can be applied to this configuration and for all the tested fluids, and a proposed figure of merit can describe the working fluids and predict their steady-state behaviour
Thermo-hydraulic performance of connected single-phase natural circulation loops characterized by two different inner diameters
No full textIn this paper, an experimental study regarding the natural circulation in connected vertical rectangular loops is presented. Typically, the geometry of the natural circulation loops (NCL) is rectangular or toroidal and the analysis is focused on the thermo-hydraulic behaviour of a single working loop. In this study, a new approach referred to several NCLs simultaneously operated was investigated. In the experimental setup, the lower heated sections of the NCLs are connected. The tests were carried out by varying the internal diameter of the loops to investigate the influence of the mutual interaction between two adjacent NCLs. The data were analyzed by the modified Vijayan's correlation showing a good agreement. A simple relationship is proposed to normalize the data both in terms of inner tube diameter and heat sink temperature. The results obtained with two NCLs characterized by different internal diameters could be considered as the first attempt to try optimizing several connected NCLs
A comprehensive study devoted to determine linear thermal bridges transmittance in existing buildings
No full textThe issue of transmittance of thermal bridges in existing buildings has been addressed aiming to achieve correlations able to evaluate the ground-contact thermal bridges. A bi-dimensional steady state FEM model has been implemented to simulate wall-to-floor structural node and then validated in accordance with the EN ISO 10211:2017 standard. Different construction joints have been then simulated for the structural node foundations-vertical elements up to a total of 19 configurations, from which 1700 cases have been derived varying walls and floor stratigraphies and ground properties. Correlations for the linear thermal bridge transmittance have been calculated through regression technique for all the configurations, together with their validity ranges expressed in terms of 95% confidence interval values. Tests performed for more than 1000 practical cases confirmed the accuracy of the proposed correlations. Through those correlations ground contact thermal bridges in existing buildings can be hence analyzed in a simple and operative way, offering technicians in the sector a tool that covers most of the possible situations
Application of PCMs to Improve Energy Efficiency in Residential Buildings
No full textThe present investigation addresses the issue of thermal insulation of building walls. In particular, the case of a wall subjected to Mediterranean climatic conditions, typical for the city of Genoa (Italy), is taken into account. A comparison between a polyurethane and a PCM layer with a thickness of 4 cm is proposed. The analysis is developed numerically by implementing a finite elements model of the wall in Comsol Multiphysics. The wall is subjected to real climatic conditions extracted from historical meteorological data and the thermal demand for heating and cooling is estimated. Both the polyurethane and the PCM have positive performances. In particular, polyurethane is more effective in reducing the heating demand, whereas PCM has better performances in reducing the cooling demand. A brief introduction to the life cycle analysis is also provided with the estimation of the energy pay-back for the two insulators and the results highlight better performance for the PCM, even though the pay-back periods of the two are quite similar
Splitting the solar radiation in direct and diffuse components; insights and constrains on the clearness-diffuse fraction representation
No full textIn many engineering applications, it is mandatory to know separately the solar radiation diffuse and direct components. Examples regard the assessment of the energy potentially exploitable by a system of solar thermal or photovoltaic panels and, in general, all the cases where it is necessary to calculate the radiative solar power collected by a surface. In fact, radiation components will differently project on the surface of interest and will weigh in a different manner, depending on the surface orientation, in the computation of the effective incident radiation. To perform this decomposition starting from data relative to a horizontal plane, two non-dimensional quantities, namely, the diffuse fraction, kd, and the clearness, kt, are usually put in mutual relation by correlating experimental data on a graphical ground rather than using physical considerations. In the present study, some insights are given on the shape of this correlation starting from geometric and physical considerations. It is shown that many results and graphs presented in literature have not physical meaning; rather they are simply artifacts due to geometrical or other constraints. These evidences open the way to a new approach to solar radiation decomposition founded on physical-based correlations
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
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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