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Evaporation/condensation around a wetted cylinder confined between two parallel walls
No full textMixed convection flows in presence of condensation and evaporation phenomena have crucial role in several natural and technological processes, in particular in those involving drying and wetting of solid surfaces. Although such flows are quite common in engineering applications, their knowledge is far from being complete.
The complex physics involved can be briefly sketched as follows: wetted solid bodies exchange heat with the liquid laying on their surfaces; the liquid phase exchange mass and heat with the surrounding gas through change of phase; the consequent diffusion of temperature and vapor concentration results in density variations that greatly impact the gaseous flow introducing buoyancy forces. In the present study we will focus on the liquid-gas interaction and we study how evaporation and condensation over solid wetted surfaces take place in an archetypal problem.
To the best of our knowledge, in literature this problem has been mostly faced, through numerical modelling (see for example [1], [2]), since uncertainties in experimental approaches may come from the difficulties to control the parameters ruling the process. The mathematical model usually adopted consists of the incompressible Navier-
Stokes equations where the buoyancy forces are taken into account by means of the Boussinesq approximation; at the wetted wall the thin liquid film is modelled as semi-permeable boundary condition which prescribes a Dirichlet condition for temperature and consequently for the saturated vapor concentration. This condition permits
evaporation/condensation of the liquid/vapor phase through the evaluation of the Stefan flow at the liquid-gas interface. The set of equations and the boundary conditions are implemented within an unsteady incompressible Navier-Stokes solver developed using the openFOAM library. The new solver has been validated against literature
numerical results of [3] in the case of laminar plane channel flow. Recent literature studies have been focused on the study of the flow moving within a straight channel with different conditions at wetted walls (among the others see [1]). In the present study we consider a more complex
situation. The flow develops in a straight channel of length L and width H. A cylinder of diameter D = 0.2H is placed inside the channel at a distance equal to L/10 from the inflow section. In order to enlighten the different interaction mechanism between the walls and the bluff body two different distances of the cylinder from the bottom wall are investigated, respectively d = H/2 and d = H/4. At the inlet uniform temperature T0 and vapor
concentration C0 are prescribed along with a parabolic velocity profile with a mean velocity U0 such that the Reynolds number Re = U0 H/ν is 500, being ν the kinematic viscosity. At the outlet a zero gradient condition is imposed together with a sponge region where fluid viscosity, thermal and concentration diffusivity are artificially
increased according to an exponential law. Moreover in the sponge region the concentration is treated as a passive scalar. The liquid film interface on the wetted cylinder has temperature Tc and concentration Cc such to allow liquid evaporation. The channel walls can be either adiabatic and impermeable or wetted with fixed temperature
Tw and concentration Cw , the latter allowing vapor condensation.
Preliminary results are here very briefly discussed and more comprehensive results will be shown at the work-shop. For the case with adiabatic and impermeable walls, the different cylinder positions yield to small differences in the Stefan flow in the overall evaporation process. The latter appears substantially steady and the evaporation
fluxes around the surface are quite homogeneous with a defect in the rear of the body. The vapor flows in the upper part of the domain and two regions of different concentration level are clearly visible. The velocity field develops in
unsteady vortices without a clear dominant size. The wetted walls condition, on the other hand, seems to greatly impact the process and especially the heat and mass transfer one. The buoyancy force and hence the characteristic velocity is increased. Downstream the body the velocity field develops in well defined vortical structures of the size
of the channel width. Near the cylinder the flow is greatly unsteady and poorly organized making the vapor well mixed. In this condition evaporation process is non homogeneous and unsteady. On the average the whole surface of the cylinder permits higher Stefan flow rates.
This study encourages further developments in order to include the liquid thin film dynamic into the model
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
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