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Numerical investigation of a double-circuit Ranque-Hilsch vortex tube
No full textThe present paper reports a numerical investigation of a double-circuit RanqueeHilsch vortex tube.
Different turbulence models, namely keε, keε RNG, SAS-SST, RSM-LRR and LES, have been tested, in
order to understand which is the most suitable for the considered problem. The analysis is conducted on
a full three-dimensional model and the results show that LES turbulence model provides the best accuracy
of temperature separation prediction, standard keε and keε RNG have the worst accuracy,
whereas RSM-LRR and SAS-SST turbulence models take an intermediate position. On the contrary, LES
model is the most expensive in terms of computational time and resources. The results obtained with LES
highlight very high radial velocity values, which result in the enhancement of the turbulent heat and
mass transfer, which implies a more accurate prediction of the temperature separation effect. The present
study concludes that LES model provides the best accuracy for the simulation of a double-circuit
RanqueeHilsch vortex tube, but at the same time RSM-LRR and SAS-SST models are a good compromise
between computational efficiency and accuracy
A comparison of the application of RSM and LES turbulence models in the numerical simulation of thermal and flow patterns in a double-circuit Ranque-Hilsch vortex tube
No full textThe present paper reports an investigation of a double-circuit Ranque-Hilsch vortex tube using a fully
three-dimensional numerical model of the turbulent compressible air flow. The main purpose of the
paper is to perform a detailed analysis of the thermal and flow patterns obtained with RSM-LRR and
LES turbulence models in order to understand which one is able to represent the Ranque-Hilsch energy
separation effect observed in a double-circuit vortex tube in the most effective way.
The LES turbulence model is found to represent the qualitative turbulence of the flow better than the
RSM-LRR model. The detailed analysis of turbulence characteristics estimated by LES model indicates that
turbulence has a significant impact on the energy separation phenomenon.
Both LES and RSM-LRR turbulence models are shown to have a weak accuracy in the prediction of the
integral characteristics of a double-circuit vortex tube.
An attempt was made to improve the results achieved with LES turbulence model by means of a grid
refinement and an increase of Smagorinsky constant value, but they were found to have a limited impact.
This leads to the conclusion that more advanced kinds of LES turbulence model should be investigated in
order to increase the accuracy of the simulation of a double-circuit vortex tube
Analysis of the local entropy generation in a double-circuit vortex tube
No full textThe method of entropy generation analysis has been implemented with the aim to investigate a double-circuit vortex tube thermodynamics. The value of the enthalpy growth rate was utilized as an indicator of the useful work done by the system. Post-processing of the numerical simulation results was carried out in order to determine the irreversible energy transformations within the computational domain. Particular attention was paid to comparative analysis of the standard k-ε and SAS-SST turbulence models from thermodynamic point of view. The near main nozzle area was mentioned as a source of irreversible energy losses because of active production of turbulence dissipation due to high local values of mean rate of strain tensor modulus. Existence of the negative work area, designated as a parasitic zone, was found in the center of the vortex tube in the close proximity to the additional flow inlet. Its formation can be explained by insufficient turbulent interactions between central and peripheral flows. It was shown that this area contributes significantly to the irreversibility and should be eliminated. The integral characteristics were developed on the ground of the three dimensional distribution of both entropy generation and enthalpy growth rate. The given characteristics are suggested to be used as objectives for the optimization studies. The vortex tube diameter, main nozzle geometry and the turbulization of the additional flow were suggested to be optimized
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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