1,720,984 research outputs found
Prediction of the liquid film distribution in stratified-dispersed gas-liquid flow
No full textA mathematical model for predicting the circumferential liquid film distribution in stratified-dispersed flow is presented. Objective of the model is to describe the typical flow conditions of wet gas transportation in long, near-horizontal pipelines. In these applications, depending on the gas velocity and pipe diameter, a large asymmetry of the liquid film distribution may arise. The model is based on the assumption that in stratified-dispersed flow, liquid droplets can only be entrained by the gas from the thick liquid layer flowing at pipe bottom. It is also assumed that the deposition of smaller droplets is related to an eddy diffusivity mechanism and regards the entire pipe circumference, while larger droplets deposit by gravitational settling on the pipe bottom. These assumptions explain the formation of a thin, non-atomizing film in the upper part of the pipe. The presence and flow structure of this film appreciably affect the pressure gradient and the liquid hold-up in the pipe and are of great importance in flow assurance studies. The model has been validated against i) the experimental observations recently published by Pitton et al. (2014), the data collected by ii) Laurinat (1982), iii) Dallman (1978), and iv) the predictions of three-dimensional CFD simulations conducted by Verdin et al. (2014). It is shown that the relevant mechanisms which are responsible for the liquid film distribution are the gravitational film drainage, droplet entrainment/deposition and wave spreading. In particular, at high gas velocities and/or small pipe diameters, the asymmetry of the liquid film diminishes owing to the wetting mechanism of wave spreading which makes the distribution of the film more uniform in the circumferential direction. As the gas velocity diminishes and/or for larger pipe diameters, wave spreading is less effective and for these flow conditions only gravitational drainage and droplet entrainment/deposition are responsible for the more asymmetric shape of the liquid film
One-dimensional model of wet gas flow in near-horizontal pipes
No full textA one-dimensional model able to predict the film distribution around the pipe wall under conditions typical of wet gas flow in near-horizontal pipes is presented. The model is based on the assumption that i) liquid droplets can only be entrained by die gas from the thick liquid layer flowing at pipe bottom and ii) the deposition of smaller droplets is related to an eddy diffusivity mechanism, while larger droplets deposit by gravitational settling mainly on the pipe bottom. The presence of a thin liquid film all around the pipe wall significantly affects the pressure gradient along the pipe. The present model is a new component of MAST (Multiphase flow Analysis and Simulation of Transitions), a transient. 1-D flow simulator developed for advanced flow assurance studies
Is it possible to reduce the cost (and increase the accuracy) of multiphase flow meters?
No full textIn the present paper, the development of a low cost multiphase flow meter, designed for an oil field where it seemed advisable to avoid the use of radioactive sources, is illustrated. This meter combines the measurements of the pressure differential through a multiphase oritice and in a vertical tube. When required, the composition of the liquid- liquid mixture can be determined with a semi-continuous sampling method. Before installation, a set of tests, performed in a laboratory where it is possible to operate at actual field conditions, allowed the development of two semi-empirical equations that enable an accurate evaluation of the gas and liquid flow rates
Dispersed bubble flow in horizontal pipes
No full textA set of experiments has been performed to analyse gas-phase distribution in horizontal bubble flow. The experimental data have been obtained by means of conductance probes and include measurements of the local void fraction and the bubble diameter and velocity. Present observations show large variations of the local void fraction and the bubble size moving from the top to the bottom of the pipe, with local maxima located close to the upper pipe wall. Measurements also show that, at the boundary of the dispersed bubble flow regime, the bubble size, and therefore the surface available for heat and mass transfer, changes abruptly for small variations of the liquid or gas flowrate. This change allows the transition between the dispersed and the elongated bubble regimes to be identified with good precision. Present data make it possible to develop a new correlation for the maximum bubble size in dispersed bubble flow
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
The effect of water in the low-temperature catalytic oxidation of hydrogen sulfide to sulfur over activated carbon
No full textThis study investigates the use of law-temperature catalytic oxidation for the removal of H2S from tail gases originating from geothermal plants, with special focus on the effect of water on the overall performance of the activated carbon catalyst. It is shown that water strongly influences the reaction rate and the total amount of sulfur that can be adsorbed on the catalyst prior to regeneration. It is suggested that the reaction takes place in a thin water layer, inside the carbon pores, from the reaction of dissolved H2S with chemisorbed oxygen
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