1,720,982 research outputs found
Eulerian Simulation of Multiphase Flows for Flotation
No full textIn the mineral industry, flotation is of great significance for the beneficiation of raw materials. It is conventionally designed at a small scale in the lab and then scaled up to
fit industrial purposes. In the upscaling and optimizing of flotation processes, knowledge of local multiphase flow variables is very valuable. Computational Fluid Dynamics (CFD) simulations in the Eulerian multi-fluid approach offer insights into such multiphase flows with the advantage of reasonable computation times. However, several gaps in their current state-of-the-art appear in the context of flotation. Most notably: (i) The hydrodynamic submodels for gas-liquid flows are developed for single bubbles, and therefore require validation and consideration of interactions at higher gas holdups. (ii) A baseline hydrodynamic model for gas-solid-liquid flows has not been established yet. (iii) Bubble-particle aggregates and flotation kinetic models need to be integrated into the simulation. In this thesis, these gaps are addressed sequentially in simple configurations that are
more amenable to analysis than full-scale flotation cells.
As will be shown, the hydrodynamic submodels for gas-liquid flows provide sufficiently accurate predictions up to medium gas holdups, primarily due to the effect of mixture
density on the pressure gradient and relative velocity. At higher holdups, the swarm effect becomes relevant, for which the literature unfortunately so far offers only inconclusive models. Furthermore, the bubble size has a significant impact on the liquid flow. For large bubbles with a negative lift coefficient, the flow becomes unstable and the gas holdup decreases as observed experimentally. The absence of bubble-induced turbulence and large gas fluxes also induce flow instability, but an appropriate validation of their mechanisms requires more elaborate models.
For gas-solid-liquid flows, divergent hydrodynamic models were used in previous studies offering little guidance. This situation is exacerbated by a scarcity of potential validation data in the literature. The attempt to nonetheless establish a baseline hydrodynamic model for such flows demonstrates the added complexity due to the presence of a third phase. A fundamental understanding of this interaction is still largely lacking.
Finally, a novel framework is developed to include flotation kinetic models for the bubble-particle attachment. For the first time, bubble-particle aggregates appear explicitly in the simulation. The implications of increasing aggregate density with particle loading can readily be studied. At the same time, the necessity to develop suitable hydrodynamic models for the aggregates becomes evident.
The work presented in this thesis has made contributions to advancing the state-of-the-art in CFD simulation of multiphase flows for flotation. Although the hydrodynamic model for gas-solid-liquid flows does not perform very well under conditions of high gas flow rates and solid fractions, the present investigation guides future efforts towards further necessary research to develop more robust closure models for such conditions and to provide comprehensive validation data. Moreover, the flotation framework enables the inclusion of a flotation kinetic model and contributes to the prediction accuracy of the simulation by capturing the impact of attachment on the buoyancy of bubble-particle aggregates. Future research should primarily focus on two key areas. The first is the development of closure models for bubble-particle aggregates, since particle attachment is known to impact the flow dynamics of the aggregates. The second is extending the framework, for example by incorporating more solid phases to account for gangue particles or cover a broad range of particle size distribution, and applying the framework to flow configurations that are more representative of flotation applications
Eulerian Simulation of Multiphase Flows for Flotation
No full textIn the mineral industry, flotation is of great significance for the beneficiation of raw materials. It is conventionally designed at a small scale in the lab and then scaled up to
fit industrial purposes. In the upscaling and optimizing of flotation processes, knowledge of local multiphase flow variables is very valuable. Computational Fluid Dynamics (CFD) simulations in the Eulerian multi-fluid approach offer insights into such multiphase flows with the advantage of reasonable computation times. However, several gaps in their current state-of-the-art appear in the context of flotation. Most notably: (i) The hydrodynamic submodels for gas-liquid flows are developed for single bubbles, and therefore require validation and consideration of interactions at higher gas holdups. (ii) A baseline hydrodynamic model for gas-solid-liquid flows has not been established yet. (iii) Bubble-particle aggregates and flotation kinetic models need to be integrated into the simulation. In this thesis, these gaps are addressed sequentially in simple configurations that are
more amenable to analysis than full-scale flotation cells.
As will be shown, the hydrodynamic submodels for gas-liquid flows provide sufficiently accurate predictions up to medium gas holdups, primarily due to the effect of mixture
density on the pressure gradient and relative velocity. At higher holdups, the swarm effect becomes relevant, for which the literature unfortunately so far offers only inconclusive models. Furthermore, the bubble size has a significant impact on the liquid flow. For large bubbles with a negative lift coefficient, the flow becomes unstable and the gas holdup decreases as observed experimentally. The absence of bubble-induced turbulence and large gas fluxes also induce flow instability, but an appropriate validation of their mechanisms requires more elaborate models.
For gas-solid-liquid flows, divergent hydrodynamic models were used in previous studies offering little guidance. This situation is exacerbated by a scarcity of potential validation data in the literature. The attempt to nonetheless establish a baseline hydrodynamic model for such flows demonstrates the added complexity due to the presence of a third phase. A fundamental understanding of this interaction is still largely lacking.
Finally, a novel framework is developed to include flotation kinetic models for the bubble-particle attachment. For the first time, bubble-particle aggregates appear explicitly in the simulation. The implications of increasing aggregate density with particle loading can readily be studied. At the same time, the necessity to develop suitable hydrodynamic models for the aggregates becomes evident.
The work presented in this thesis has made contributions to advancing the state-of-the-art in CFD simulation of multiphase flows for flotation. Although the hydrodynamic model for gas-solid-liquid flows does not perform very well under conditions of high gas flow rates and solid fractions, the present investigation guides future efforts towards further necessary research to develop more robust closure models for such conditions and to provide comprehensive validation data. Moreover, the flotation framework enables the inclusion of a flotation kinetic model and contributes to the prediction accuracy of the simulation by capturing the impact of attachment on the buoyancy of bubble-particle aggregates. Future research should primarily focus on two key areas. The first is the development of closure models for bubble-particle aggregates, since particle attachment is known to impact the flow dynamics of the aggregates. The second is extending the framework, for example by incorporating more solid phases to account for gangue particles or cover a broad range of particle size distribution, and applying the framework to flow configurations that are more representative of flotation applications
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
