1,720,957 research outputs found
Multiple impinging jet arrays. An experimental study on flow and heat transfer
No full textBecause of their high efficiency and their ability to provide high heat transfer rates, impinging jets are applied for rapid cooling and heating in a wide variety of industrial processes. However, the physical phenomena controlling the heat transfer from impinging jets are to a large degree unknown. The goal of the present project was to gain a better understanding of the interaction between the flow and heat transfer in impinging jet arrays. Experiments were performed in two different configurations: a single impinging jet and multiple impinging jet arrays. LDA and PIV velocity measurements in the single jet were compared: these measurements were aimed at serving as a reference for comparison of the multiple jet features. In a hexagonal and an in-line array of jets PIV was used to provide instantaneous velocity fields over the flow area of interest, what proved to be essential for detecting some salient features of the multiple-jet dynamics. These dynamics were investigated on the basis of POD filtered snapshots of the flow. In both arrays, large scale eddies in the development zone cause the impinging jets to break up or be severely displaced in the out-of-plane direction. A horse-shoe vortex appears around the outer jets of the hexagonal array, whereas the in-line array does not show this feature. This is most likely caused by the higher pitch in the in-line configuration. On the other hand, the flow field in the in-line arrangement appears to be diagonally asymmetrical, even though the symmetry of the nozzle arrangement would imply a symmetrical flow field. This flow asymmetry causes an elliptical heat transfer pattern in the impingement zone of the center jet. The flow asymmetry was also found in numerical simulations of a similar configuration, conducted in a parallel project. Heat transfer measurements were performed in the impingement surface for seven multiple jet arrays using LCT, which provided insight in the influence of different geometrical parameters of the arrays on the heat transfer. Additionally, a non-dimensional correlation was derived linking heat transfer to geometrical and flow parameters. Heat transfer profiles were subsequently compared to velocity and turbulence quantities just above the impingement plate to investigate the effect of the mean flow features on the heat transfer. The apparent correlation between the Nusselt number and the normal contribution to the production of turbulent kinetic energy is coincidental: the cause of the increased Nusselt number in the impingement points of the jets is a combination of an oscillating impingement position due to large vortical structures and a very strong acceleration of the fluid from the impingement point outwards. In the impingement point the boundary layer is very thin and the temperature gradient is very steep, enabling impinging vortices to encapsulate and remove heat in an effective way. The results presented in this thesis should aid in better understanding the role of turbulence and vortical structures in the interaction between adjacent impinging jets, and in the heat transfer from impinging jets. With the advent of a measurement technique capable of capturing instantaneous heat transfer distributions, a potential extension of the present work is a more detailed analysis of the influence of individual vortical structures on impingement heat transfer.Applied Science
Optimization of particle image velocimetry for turbulent stirred tank flow
No full textThis project was aimed at optimizing Particle Image Velocimetry (PIV) for the determination of velocity distributions in turbulent stirred tank flow. To resolve directional ambiguity, which is inherently linked to PIV, a rotating mirror was used. Two procedures to correct for the applied pre-shift were tested. At Re=5000, five different configurations of the PIV-system were tried. These configurations were different from each other in the choice of recording angle, particle concentration and pre-shift velocity. Two of these five configurations yielded pictures with sufficient quality. The pictures of these two configurations were analysed digitally by two correlation procedures, i.e. auto-correlation and cross-correlation with shifted interrogation areas (SIA). In the latter method, auto-correlation was used to determine the integer displacement of particle images. This integer displacement field was used as window shift field for the cross-correlation procedure with a view to minimizing the loss of pairs effect by in-plane movement. Additionally, a multiple pass method was proposed and its performance tested. The purpose of this method was to increase the resolution of the analysis by decreasing the size of the interrogation areas. Mean and RMS velocity profiles were constructed from the determined velocity fields. These profiles are compared to profiles resulting from LDA experiments in a similar tank.Kramers Laboratorium voor Fysische TechnologieApplied Science
Particle image velocimetry in turbulentie onderzoek: Een literatuurscriptie
No full textApplied SciencesKramers Laboratorium voor Fysische Technologi
Wall imprint of turbulent structures and heat transfer in multiple impinging jet arrays
No full textApplied Science
Verbeterde procesvoering van het bietensapzuiveringsproces, zoals momenteel toegepast door Suiker Unie
No full textDelftChemTechApplied Science
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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