1,720,975 research outputs found
CFD modeling of emulsions inside static mixers
Full text linkEmulsification carried out in continuous devices offers a series of advantages over batch emulsion, such as better control of the droplet size distribution, reduced volume equipment, and lower operative costs. This paper investigates through Computational Fluid Dynamics simulations the emulsification process inside Sulzer Static Mixers. An analysis aimed to identify the most appropriate turbulence model, from a practical point of view, was performed, finding that the realizable Kappa – Epsilon model is more suitable than the well-known Kappa - Omega model. Moreover, an operative correlation linking the Sauter diameter to the main operating parameters, in a wide range of fluid properties and operating conditions, was developed
From semi-batch to continuous tubular reactors: A kinetics-free approach
Full text linkA methodology, which does not require any kinetic information, for the rigorous transformation of an isothermal, homogeneous semi-batch process into an equivalent continuous side-fed tubular reactor was developed. Once the semi-batch process parameters are known, the proposed methodology allows for easily defining all the process parameters of a side-fed tubular reactor that guarantees the same performances as the original semi-batch process, in terms of conversion and product characteristics. Two different case studies were selected to investigate the potential of the proposed approach: a copolymer synthesis and the production of a fine chemical, clearly showing the need of a rigorous transformation of the semi-batch process into the continuous one since productivity and product quality are strongly affected by the feeding policy
Kinetics-free transformation from non-isothermal discontinuous to continuous tubular reactors
Full text linkFocusing on tubular reactors with continuously distributed side injections, a general procedure to evaluate the operating mode able to reproduce the performance of a given semi-batch reactor is worked out. Namely, such operating mode is expressed as axial profiles of feed flowrate and temperature of the cooling/heating medium inside the reactor jacket. This transformation procedure, previously limited to isothermal reactors, is extended here to non-isothermal systems. The process performance (selectivity and conversion) of the original discontinuous reactor are fully reproduced using the continuous intensified reactor, while its productivity remains a degree of freedom. Notably, like in the isothermal case, the transformation procedure is kinetics-free, i.e. the knowledge of the reaction kinetics is not a precondition. As case study, a copolymerisation reaction is considered to demonstrate the potential of the method. Even though any SBR feed policy could be considered when applying this methodology, the optimal feed policy of the semi-batch reactor evaluated according to the so-called “power feed” procedure is examined considering the reactor non-isothermal. Afterwards, the proposed transformation method is applied and the performance of the two systems, discontinuous and continuous, are comparatively evaluated. Finally, given the practical difficulties associated with continuously distributed side injections, a discretisation approach is proposed based on the use of discrete lateral feeds and more realistic reactor configurations
Mixing Efficiency and Residence Time Distributions of a Side-Injection Tubular Reactor Equipped with Static Mixers
Full text linkPlug flow behavior in tubular reactors is often
highly desirable in industry, since it can ensure high productivity,
good selectivity, and enhanced heat transfer. To achieve this, good
radial mixing combined with poor axial mixing is required: these
conditions are quite easy to obtain if the flow regime is turbulent,
but they are much more challenging to achieve if the flow is
laminar. In this work radial mixing and residence time distributions
in a side-injected tubular reactor equipped with a series of Sulzer
SMX static mixers were investigated using Computational Fluid
Dynamics. It was found that even at low values of Reynolds
number the reactor can efficiently satisfy the plug flow conditions,
and operative diagrams were determined to foresee the reactor
behavior
Development of a Generalised Equilibrium Modified Atmosphere Model and its Application to the Taleggio Cheese
Full text linkThe food metabolic processes influence the gas composition of packaged products: by finely tuning the gas fluxes through the packaging, the aerobic and anaerobic respiration processes can be efficiently exploited to regulate the equilibrium gas concentrations. In this work, we present a generalised model able to predict the evolution of gases in micro-perforated equilibrium MAP, with a detailed evaluation of fluxes through the perforations by means of Computational Fluid Dynamics. It was found that the Sherwood number for the studied micro-perforations is 0.715 and it was confirmed via experiments on packaging with oxygendepleted atmospheres. The kinetic model was experimentally validated on a smear short-ripened soft cheese (Taleggio) whose complex surface microbiota confer to the product a non-trivial respiration behaviour. Cheese slices were packed with three different micro-perforated solutions (one 120 μm diameter hole, two 90 μm diameter holes, and five 90 μm diameter holes) achieving three different equilibrium gas compositions with good model predictions. The model was applied to literature data with success, thus the model can be deemed general and applicable to many different systems
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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