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Data for "Novel flow modulation method for R744 two-phase ejectors – Proof of concept, optimization and first experimental results"
No full textExperimental data of CO2 transcritical system with and without ejector.Data belongs the article "Novel flow modulation method for R744 two-phase ejectors – Proof of concept, optimization and first experimental results".The
research leading to these results has received funding from the European
Union’s Horizon 2020 research and innovation programme under the Marie
Skłodowska-Curie grant agreement No. 844924 (Project: ECO2-RAPJECT)Contact person for dataset: Paride Gullo, ORCID:
0000-0001-9256-875X</div
A novel capacity control mechanism for two-phase ejectors in transcritical R744 air conditioners
No full textPresentation at the ATMO/DTI Technical Conference on “The Future of Air Conditioning
Preliminary experimental investigation on a transcritical R744 condensing unit using the novel PWM ejector
No full textIn this work the preliminary experimental performance study on an innovative control technique for two-phase ejectors in transcritical R744 condensing units is presented. Currently two-phase ejectors cannot be properly capacity controlled without sacrificing ejector and system efficiency in these units. The novel capacity control methodology involves the pulse-width modulation (PWM) of the refrigerant flow through the ejector. At the compressor speed of 50 Hz, water temperatures at the gas cooler inlet between 30 °C and 40 °C and R744 evaporating temperature of roughly -5.5 °C, the collected data revealed that the discharge pressure can be appropriately controlled as well as increased by up to about 28 bar. Also, at the optimum operation conditions the unit with the PWM ejector presented enhancements in coefficient of performance (COP) by between 10.0% and 12.1% over the system using the passive ejector and by between 23.7% and 31.2% compared to the solution with flash gas by-pass valve. Finally, the proposed methodology presents low cost, simplicity, low vulnerability to clogging and much more significant potential than its today’s available competitors
Novel flow modulation method for R744 two-phase ejectors – Proof of concept, optimization and first experimental results
No full textThe cooling industry involves various essential applications, such as food preservation, medicine storage and air conditioning. However, its significant direct and indirect contribution to global warming is bound to increase in years to come, leading to the need for highly efficient cooling units using eco-friendly working fluids. Consequently, carbon dioxide (R744) is achieving resounding success as a refrigerant for various medium- and large-capacity applications, as some of the available expansion work is recovered with the aid of two-phase ejectors. However, its adoption is being limited for small-capacity solutions (e.g. condensing units) due to the current lack of a suitable flow modulation technique for two-phase ejectors installed in these units. Therefore, the goal of this work is to bridge this knowledge gap by formulating and experimentally proving an innovative flow control mechanism for two-phase ejectors, being based on the pulse-width modulation (PWM) of the refrigerant flow through the ejector. All the experimental evaluations were carried out at the compressor speed of 50 Hz, water temperature at the gas cooler inlet of 35 °C and R744 evaporating temperature of about −5 °C.
The first experimental data revealed that the high pressure can be controlled appropriately as well as varied from about 87 bar to 112 bar, demonstrating the effectiveness of the proposed technique. In addition, the effect of the muffler volume as well as the PWM period on the ejector and system performance were investigated. It was found that the influence of both the muffler volume and the PWM period was not significant. Compared to the solution employing the passive ejector (i.e. without flow modulation technique), the unit with the PWM ejector presented enhancements in coefficient of performance (COP) by more than 5% at the optimum operation conditions. It is worth mentioning that its today’s available competitors, i.e. needle-based ejector and vortex-based ejector, feature COP enhancements by 2%–4% as contrasted with the passive ejector. As benchmarked to the standard unit (i.e. with flash gas by-pass valve and without ejector), the PWM ejector could improve the COP by more than 10% at the optimal running conditions. Also, the results obtained suggest that at present the proposed solution should operate with a PWM period of 2 s and no mufflers. Finally, the PWM ejector is characterized by low cost, simplicity, low vulnerability to clogging and no practical size or application constraints
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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