1,720,958 research outputs found
A Volume-of-Fluid method for multicomponent droplet evaporation with Robin boundary conditions
Get PDFWe propose a numerical method tailored to perform interface-resolved simulations of evaporating
multicomponent two-phase flows. The novelty of the method lies in the use of Robin boundary
conditions to couple the transport equations for the vaporized species in the gas phase and the
transport equations of the same species in the liquid phase. The Robin boundary condition is
implemented with the cost-effective procedure proposed by Chai et al. [1] and consists of two
steps: (1) calculating the normal derivative of the mass fraction fields in cells adjacent to the
interface through the reconstruction of a linear polynomial system, and (2) extrapolating the
normal derivative and the ghost value in the normal direction using a linear partial differential
equation. This methodology yields a second-order accurate solution for the Poisson equation with
a Robin boundary condition and a first-order accurate solution for the Stefan problem. The overall
methodology is implemented in an efficient two-fluid solver, which includes a Volume-of-Fluid
(VoF) approach for the interface representation, a divergence-free extension of the liquid velocity
field onto the entire domain to transport the VoF, and the temperature equation to include thermal
effects. We demonstrate the convergence of the numerical method to the analytical solution for
multicomponent isothermal evaporation and observe good overall computational performance
for simulating non-isothermal evaporating two-fluid flows in two and three dimensions
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
On the influence of liquid/vapor phase change onto the Nusselt number of a laminar superheated or subcooled vapor flow
Get PDFBased on a numerical approach, we propose in this study to characterize the interaction between a laminar boundary layer of a superheated or subcooled vapor flow and a static liquid pool at saturation temperature. For the purpose of this study, we define a canonical configuration that will help to improve our physical understanding of the interaction between a laminar flow and vaporization or condensation. By performing a full set of simulations sweeping the parameters space, correlations are proposed for the first time on the Nusselt number depending on the dimensionless numbers (the Reynolds number, the Prandtl number, the Jakob number and the density ratio) that characterize both vaporization and condensation. As attended, the Nusselt number decreases or increases in the configurations involving vaporization or condensation respectively. For high Jakob number, opposite trends are observed depending whether if vaporization or condensation is considered. Indeed a saturation of the heat flux happens in the first case, whereas a self-amplification of the heat flux occurs in the second one. Since the Nusselt number expressions are known, analytical expressions for the integrated heat flux exchanged at the liquid/vapor interface can be determined. Our study also takes interest to the behaviour of the viscous friction of the vapor flow on the liquid pool, which is weakly affected by the phase change, despite the important variation of the local flow structure due to evaporation or condensation. The physical mechanisms inducing all these phenomena are here discussed and clarified
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
Numerical simulation of the interaction between an external flow, laminar or turbulent, and liquid/vapor phase change
Get PDFIn a launcher tank, the cryogenic fuel can suffer a liquid/vapor phase change due to a thermal gradient induced by solar radiation or by engines residual thermal diffusion. The quantity of vapor released by the phase change process can highly increase the internal pressure. Due to a poor knowledge of these phenomena, at present, the operations led to regulate the internal pressure induce fuel loss. It is therefore of great importance to investigate the liquid/vapor phase and the physical processes taking place at the interface. This is the context of the present thesis, thattakes place in an effort to extract better understanding of the above underlined phenomena by means of Direct Numerical Simulation (DNS). The work is split into three studies : the interaction between a liquid pool at saturation and an external flow of subcooled or superheated vapor, both in laminar and turbulent regime flows, and the interaction between natural convection mouvements and liquid/vapor phase change. Firstly, the laminar regime flow is investigated. In this framework, a parametric study is conducted with the objective of finding behaviour laws for the heat transfer and the friction coefficient at the interface between a static liquid pool at saturation temperature and a laminar boundary layer flow of vapor. Both vaporization and condensation are studied. The second project was on the numerical simulation of a turbulent boundary layer flow of superheated vapor interacting with the velocity field induced by vaporization. To this extent, a turbulent fluctuations injector is implemented and validated for the spatial development of a boundary layer flow over a flat plate with heat transfer. A study on the influence of the velocity field induced by vaporization on the Nusselt number, the friction coefficient, the Stanton number and the turbulent quantities is conducted. Finally, we lead a preliminary numerical study on a configuration describing the interaction between natural convection flow and liquid/vapor phase change in a cryogenic tank. A new solver is implemented in the in house code to account for the density variations in the liquid. Preliminary results are obtained on the influence of the Grashof number on the thermal flux at the liquid/vapor interfac
Simulation numérique de l'interaction entre un écoulement externe, laminaire ou turbulent, et un changement de phase liquide/vapeur
No full textIn a launcher tank, the cryogenic fuel can suffer a liquid/vapor phase change due to a thermal gradient induced by solar radiation or by engines residual thermal diffusion. The quantity of vapor released by the phase change process can highly increase the internal pressure. Due to a poor knowledge of these phenomena, at present, the operations led to regulate the internal pressure induce fuel loss. It is therefore of great importance to investigate the liquid/vapor phase and the physical processes taking place at the interface. This is the context of the present thesis, thattakes place in an effort to extract better understanding of the above underlined phenomena by means of Direct Numerical Simulation (DNS). The work is split into three studies : the interaction between a liquid pool at saturation and an external flow of subcooled or superheated vapor, both in laminar and turbulent regime flows, and the interaction between natural convection mouvements and liquid/vapor phase change. Firstly, the laminar regime flow is investigated. In this framework, a parametric study is conducted with the objective of finding behaviour laws for the heat transfer and the friction coefficient at the interface between a static liquid pool at saturation temperature and a laminar boundary layer flow of vapor. Both vaporization and condensation are studied. The second project was on the numerical simulation of a turbulent boundary layer flow of superheated vapor interacting with the velocity field induced by vaporization. To this extent, a turbulent fluctuations injector is implemented and validated for the spatial development of a boundary layer flow over a flat plate with heat transfer. A study on the influence of the velocity field induced by vaporization on the Nusselt number, the friction coefficient, the Stanton number and the turbulent quantities is conducted. Finally, we lead a preliminary numerical study on a configuration describing the interaction between natural convection flow and liquid/vapor phase change in a cryogenic tank. A new solver is implemented in the in house code to account for the density variations in the liquid. Preliminary results are obtained on the influence of the Grashof number on the thermal flux at the liquid/vapor interfaceDans le réservoir d’un satellite, le carburant cryogénique peut se transformer en vapeur à cause de la présence d’un gradient de température à la paroi, induit par le rayonnement solaire ou la diffusion thermique résiduelle des moteurs du lanceur. La quantité de vapeur transformée peut fortement augmenter la pression à l’intérieur du réservoir. En raison d’une connaissance incomplète des ces phénomènes, aujourd’hui, les opérations faites pour régulariser la pression interne entraînent une perte de carburant. Il est donc très important d’étudier le changement de phase liquide/vapeur et les processus physiques mis en jeu au niveau de l’interface. C’est dans ce contexte que se situe cette thèse, dont l’objectif est d’obtenir une meilleure compréhension des phénomènes susmentionnés au moyen de la Simulation Numérique Directe (DNS). Le travail estdivisé en trois parties : l’interaction entre un liquide à température de saturation et un écoulement externe de vapeur sous-refroidie ou surchauffée, en régime laminaire et turbulent, et l’interaction entre des mouvements de convection naturelle et le changement de phase liquide/vapeur. Tout d’abord, le régime laminaire est étudié. Dans ce cadre, une étude paramétrique est menée dont l’objectif est de trouver des lois de comportements pour le transfert thermique et le coefficient de frottement à l’interface entre un liquide statique à température de saturation et un écoulement decouche limite de vapeur. Nous étudions à la fois la vaporisation et la condensation. La seconde partie de cette thèse est dédiée à la simulation numérique d’un écoulement de couche limite turbulente d’une vapeur surchauffée en interaction avec un champ de vitesse induit par de la vaporisation. Pour cela, un injecteur de turbulence est implémenté dans le code et validé pour la configuration de l’évolution spatiale d’une couche limite turbulente sur une plaque plane avec transfert thermique. Ensuite, une étude sur l’influence du champ de vitesse induit par la vaporisation sur le nombre de Nusselt, le coefficient de frottement, le nombre de Stanton et les différentes quantités turbulentes est réalisée. Enfin, nous menons une étude numérique préliminaire sur une configuration décrivant l’écoulement convectif dans un réservoir cryogénique. Un nouveau solveur est implémenté dans le code utilisé afin de prendre en compte les variations de la densité. Des résultats préliminaires sont obtenus sur l’influence du nombre de Grashof sur le flux thermique à l’interface liquide/vapeu
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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