1,720,975 research outputs found
Experimental validation of a two equation RANS transitional turbulence model for compressible microflows
Full text linkLaminar-to-turbulent flow transition in microchannels can be useful to enhance mixing and heat transfer in microsystems. Typically, the small characteristic dimensions of these devices hinder in attaining higher Reynolds numbers to limit the total pressure drop. This is true especially in the presence of a liquid as a working medium. On the contrary, due to lower density, Reynolds number larger than 2000 can be easily reached for gas microflows with an acceptable pressure drop. Since microchannels are used as elementary building blocks of micro heat exchangers and micro heat-sinks, it is essential to predict under which conditions, the laminar-to-turbulent flow transition inside such geometries can be expected. In this paper, experimental validation of a two equations transitional turbulence model, capable of predicting the laminar-to-turbulent flow transition for internal flows as proposed by Abraham etal. (2008), is presented for the first time for microchannels. This is done by employing microchannels in which Nitrogen gas is used as a working fluid. Two different cross-sections namely circular and rectangular are utilized for numerical and experimental investigations. The inlet mass flow rate of the gas is varied to cover all the flow regimes from laminar to fully turbulent flow. Pressure loss experiments are performed for both cross-sectional geometries and friction factor results from experiments and numerical simulations are compared. From the analysis of the friction factor as a function of the Reynolds number, the critical value of the Reynolds number linked to the laminar-to-turbulent transition has been determined. The experimental and numerical critical Reynolds number for all the tested microchannels showed a maximum deviation of less than 12%. These results demonstrate that the transitional turbulence model proposed by Abraham etal. (2008) for internal flows can be extended to microchannels and proficiently employed for the design of micro heat exchangers in presence of gas flows
Numerical investigation of compressibility effects on friction factor in rectangular microchannels
Full text linkThis study numerically investigated the effect of gas compressibility on the friction factor in rectangular microchannels. The numerical model adopted in the study was validated against experimental data obtained by testing rectangular microchannels with a hydraulic diameter of 295 μm. The numerical model was used to evaluate the Reynolds number at which the compressibility effects on the friction factor became significant by analyzing the role of both hydraulic diameter and aspect ratio of the microchannel. To this end, three values of the hydraulic diameter (100, 295, and 500 μm) and five different aspect ratios (from 0.25 to 1) were investigated. The results showed that compressibility effects became increasingly stronger by reducing the hydraulic diameter and that they led to an increase in the average friction factor. For smaller microchannels, the Reynolds numbers at which the compressibility effects became significant tended to reduce and were in the laminar regime. The gas compressibility could not be ignored when friction factors needed to be accurately determined. Moreover, for narrow microchannels (low aspect ratio), compressibility effects became important for higher values of the Reynolds number than those observed for nearly squared microchannels
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
Effect of Aspect Ratio of Rectangular Microchannels on Laminar-to-turbulent Transition for Compressible Flows
No full textAppropriate 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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