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Dewetting Dynamics of Heavy Crude Oil: Contributions from Surface and Interfacial Forces
Get PDFThe research considers the dewetting dynamics of heavy crude oil on solid substrates in the presence of chemical additives and at elevated temperatures and pressures. Increasing the temperature from 40 to 80 °C was found to increase the initial receding rate of an oil droplet on substrate from 0.07 to 3.73 °/s, a consequence of the reduced oil viscosity. Higher temperatures also induced release of natural surfactants and thus decreased the oil-water interfacial tension (σ_OW), promoting increased oil droplet dewetting (equilibrium contact angle (θ) decreased from 63.7° to 51.3°), with the effect described by the Young’s equation. At high pressure (200 bar at 140 °C), asphaltenes partition less at the oil-water interface leading to slightly higher σ_OW (14.4 mN/m at 10 bar to 17.6 mN/m at 200 bar). Increase in σ_OW led to less oil dewetting as the θ increased from 17.9° to 23.1°. Adding a surfactant demonstrated the benefit of reducing σ_OW and increasing oil-substrate electrostatic repulsion. At high surfactant concentration the oil droplet attained low θ, and eventually pinched-off from the surface when the ultra-low oil-surface adhesion was exceeded by droplet buoyancy.
Oil droplet dewetting was studied in brine fluids at 60 °C where the addition of salt was shown to change σ_OW depending on the synergistic interfacial adsorption of salt ions and native surface-active species (i.e. naphthenic acids and asphaltenes). However, the oil droplet contact angles in brines were more influenced by the disjoining pressure and not σ_OW as described by the Young’s equation. Increased oil droplet dewetting (θ: 43.2° in water → 18.1°) was observed in low-salinity NaCl fluid (2,000 ppm), with hydration forces strongly influencing repulsion between the oil droplet and substrate. In contrast, attractive hydrophobic forces, as measured in CaCl2 brines, acting between the oil droplet and hydrophobised substrate (via divalent cation bridging), reduced the oil droplet dewetting rate and increased θ (≥ 27.2° at 60 °C). Initial droplet receding rates were increased by a strong oil-substrate repulsion and low steady-state θ, without the influence of changing σ_OW.
Surface-active nanoparticles, poly(N-isopropylacrylamide) (PNIPAM), were synthesised to study their effect on lowering σ_OW and enhancing the dewetting dynamics in the presence of surfactant. Blends of PNIPAM and SDS (1:1 mass ratio) were considered at different bulk concentrations. At low concentration (5 × 10-4 wt%), SDS interfacial adsorption was greater than PNIPAM with the dominance reversed at high concentration (5 × 10-3 wt%). The difference in interfacial activity was shown to influence the oil dewetting process, but is not fully described by the Young’s equation. Increased oil dewetting by nanoparticles was shown at low concentration, with the PNIPAM and SDS blend displacing the oil droplet at 5.66 °/s and attaining low θ (37.0°), while σ_OW remained relatively high (25.3 mN/m). This was due to PNIPAM particles remaining in the bulk fluid and self-assembling in the oil-water-substrate “wedge”, thus inducing a structural disjoining pressure, which promoted oil dewetting. In the presence of NaCl (2,000 ppm), contributions from PNIPAM induced further structural forces that led to a gradual liberation of oil from the substrate, even though the droplet buoyant force was less than the oil-substrate adhesion force
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
Crude Oil Displacement Enhanced by Interfacially Active Nanoparticles and Their Coupling Effect with Low-Salinity Brines
Get PDFFrom the microscopic scale to the petroleum-reservoir scale, the interfacial phenomena of the crude oil-water-rock system crucially control an immiscible flow in a porous reservoir. One of the key mechanisms is crude oil droplet displacement dynamics, which can be optimized by manipulating the oil-water interfacial tension and the three-phase contact angle by means of chemical injection. The current study primarily investigated oil displacement enhanced by interfacially active nanoparticles, namely poly(N-isopropylacrylamide) or pNIPAM, which found an acceleration of oil droplet receding rate (5.66 degree/s) and a greater degree of oil droplet dewetted (37.0 degree contact angle). This was due to a contribution from the nanoparticle-induced structural disjoining pressures between the oil-water and water-solid interfaces. The coupling effect of pNIPAM nanoparticles with low-salinity brines was examined, which revealed a discrepancy in different brine valences. Coupling with divalent CaCl2 led to much slower oil droplet receding dynamics (2.58 degree/s, and 58.7 degree contact angle) since oil-substrate bridging is formulated and promoted by the divalent cation. However, positive synergy was observed with a monovalent NaCl blend. The crude oil dewetting dynamics were enhanced (9.55 degree/s) owing to the combined salt-induced hydration and nanoparticle-induced structural forces. The contact angle was as low as 21.5 degree before eventually detaching from the substrate for a relatively short period (156 s). These findings highlight the coupling effect of nanoparticles and low-salinity brine on the dewetting of heavy crude oil. Adding nanoparticles to an optimal brine could be an option for faster and greater fluid displacement, which is not limited to oil production applications but several others, such as detergency and other forms of geological storage.15 page
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
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