The pear-shaped fate of an ice melting front

A fluid-structure interaction problem with the melting of water around a heated horizontal circular cylinder is analysed with numerical simulations. Dynamic meshing was used for evolving the flow domain in time as the melting front extended radially outward from the cylinder; a node shuffle algorithm was used to retain mesh quality across the significant mesh deformation. We simulated one case above the density inversion point of water and one case below, yielding pear-shaped melting fronts due to thermal plumes either rising or falling from the cylinder, respectively. Results were compared with previous experimental studies and the melting front profiles matched reasonably well and melting rates were in agreement. We confirm that natural convection plays a significant role in the transport of energy as the melt zone increases, and needs to be considered for accurately modelling phase change under these conditions.Comment: Accepted for the 12th International Conference on CFD in Oil & Gas, Metallurgical and Process Industries. SINTEF, Trondheim, Norway. May 30th - June 1st, 201

The numerical simulation of thin film flow over heterogeneous substrates

Considerable progress in the understanding of thin film flow over surfaces has been achieved thanks to lubrication theory which enables the governing Navier-Stokes equations to be reduced to a more tractable form, namely a coupled set of partial differential equations. These are solved numerically since the flows of interest involve substrates containing heterogeneities in the form of wetting patterns and/or topography. An efficient and accurate numerical method is described and used to solve two classes of problem: droplet spreading in the presence of wetting and topographic heterogeneities; gravity-driven flow of continuous thin liquid films down an inclined surface containing well defined topographic features. The method developed, employs a Full Approximation Storage (FAS) multigrid algorithm, is fully implicit and has embedded within it an adaptive time-stepping scheme that enables the same to be optimised in a controlled manner subject to a specific error tolerance. Contact lines are ubiquitous in the context of droplet spreading and the wellknown singularity which occurs there is alleviated by means of a disjoining pressure model. The latter allows prescription of a local equilibrium contact angle and three dimensional numerical simulations reveal how droplets can be forced to either wet or dewet a region containing topography depending on the surface wetting characteristics. The growth of numerical instabilities, in the contact line region, which can lead to the occurrence of non-physical, negative film thicknesses is avoided by using a Positivity Preserving Scheme. A range of two- and three-dimensional problems is explored featuring the gravity-driven flow of a continuous thin liquid film over a non-porous inclined flat surface containing topography. Important new results include: the quantification of the validity range of the lubrication approximation for step-up and step-down topographies; description of the "bow wave" triggered by localised topography and an explanation, in terms of the local flow rate, of the accompanying "downstream surge": an assessment of linear superposition as a means of examining free surface response to topographies. In addition, the potential of local mesh refinement as a means of reducing computational time is highlighted. Finally, more complex liquids composed of a non-volatile resin dissolved in a solvent and allowed to evaporate are considered. An evaporation model based on the wellmixed approximation is utilised. Results show that localised topographies produce defects in dried continuous films which persist far downstream of the topography, while with respect to droplet motion, solvent evaporation is found to be responsible for contact line pinning and thus a reduction in spreading

Modelling ripple morphodynamics driven by colloidal deposition

Fluid dynamics between a particle-laden flow and an evolving boundary are found in various contexts. We numerically simulated the morphodynamics of silica particle deposition from flowing water within geothermal heat exchangers using the arbitrary Lagrangian-Eulerian method. The silica particles were of colloidal size, with submicron diameters, which were primarily transported through the water via Brownian motion. First, we validated the Euler-Euler approach for modelling the transport and deposition of these colloidal particles within a fluid by comparing our simulation results with existing experiments of colloidal polystyrene deposition. Then we combined this multiphase model with a dynamic mesh model to track the gradually accumulated silica along the pipe walls of a heat exchanger. Surface roughness was modelled by prescribing sinusoidally-shaped protrusions on the wall boundary. The silica bed height grew quickest at the peaks of the ripples and the spacing between the protrusions remained relatively constant. The rough surface experienced a 20 % reduction in silica deposition when compared to a smooth surface. We also discuss the challenges of mesh deforming simulations with an emphasis on the mesh quality as the geometry changes over time

La construcción social de la fibromialgia como problema de salud a través de las políticas y la prensa en España

Antecedentes/Objetivos: La fibromialgia (FM) es una enfermedad crónica dolorosa recientemente reconocida que afecta principalmente a las mujeres. El objetivo de este estudio es analizar la emergencia y visibilidad de la FM como un problema de salud en las políticas sanitarias, iniciativas parlamentarias (IP) y noticias de prensa en España. Métodos: Este estudio está estructurado en tres análisis independientes pero relacionados entre sí, acerca de la visibilización de la FM como un problema de salud desde distintos enfoques metodológicos y fuentes de información. Para ello se realizaron búsquedas sistemáticas a través de Internet y análisis de contenido cualitativo de los planes de salud autonómicos, noticias de prensa (El País, El Mundo y ABC) e iniciativas parlamentarias (IP) en España hasta el año 2013. Resultados: Los planes de salud no incluyen la FM entre los problemas de salud que priorizan en sus estrategias. Las IP reflejan la desproporcionada prevalencia femenina de la FM y denuncian su difícil diagnóstico, la falta de recursos destinados a la investigación y a su tratamiento, así como la falta de reconocimiento social y de las incapacidades laborales. La prensa refleja el estereotipo de enferma de las pacientes, pasivas y resignadas, que por el contrario cobran fuerza en grupo mediante las asociaciones, representadas como activas y luchadoras, quienes han conseguido llegar al Parlamento y tener impacto en las políticas. Ambos análisis indican que el año 2002 supuso un punto de inflexión en el reconocimiento social de la enfermedad, debido a la popularización del caso de particular de la diputada del PSOE en Cataluña, Manuela de Madre, a quien se le diagnosticó FM. Conclusiones: La incipiente incorporación de la FM en la agenda parlamentaria española y su cobertura periodística tienen un impacto positivo, puesto que promueven el conocimiento y la sensibilización social sobre este problema de salud. Aún así, los resultados muestran que la construcción social de la FM como problema de salud se encuentra en fase de decrecimiento gradual de interés. Además, la falta de reconocimiento social de la enfermedad puede estar relacionada con que se construye socialmente como un problema de salud de mujeres, con estereotipos de género.Centro de Estudios sobre la Mujer (CEM), Universidad de Alicante

How valid is Taylor dispersion formula in slugs?

In a landmark paper, Taylor predicted that shear flow increases the effective diffusivity of species [Taylor, Proc. Roy. Soc. A, 219:186-203,1953]. This paper focused on Poiseuille flow in a circular pipe and predicted the existence of an effective species diffusion much greater than molecular diffusion. The ratio between the effective and molecular diffusion was shown to scale with the square of the Peclet number (product of the pipe diameter with the mean flow velocity divided by the molecular diffusivity). Taylor's study assumed two infinite columns of miscible fluids initially juxtaposed in a pipe and transported by the flow. A question of high practical interest is how valid this prediction is when a finite-sized slug is considered instead of an infinite fluid column. This paper sheds light on the finite-size effects on the mixing of two miscible fluids in a slug and quantifies how accurate Taylor's prediction is for finite length liquid columns. Results show that Taylor's dispersion formula is most accurate for lower Peclet numbers and longer slugs. Results also show that mixing is quite insensitive to the Reynolds number. References Daniel A Beard. Taylor dispersion of a solute in a microfluidic channel. Journal of Applied Physics, 89(8):4667–4669, 2001. doi:10.1063/1.1357462. J Bico and D Quere. Liquid trains in a tube. EPL (Europhysics Letters), 51(5):546, 2000. doi:https://doi.org/10.1209/epl/i2000-00373-4. Jose Bico and David Quere. Falling slugs. Journal of colloid and interface science, 243(1):262–264, 2001. doi:https://doi.org/10.1006/jcis.2001.7891. Jose Bico and David Quere. Self-propelling slugs. Journal of Fluid Mechanics, 467:101–127, 2002. doi:10.1017/S002211200200126X. Wolfgang Buchegger, Christoph Wagner, Bernhard Lendl, Martin Kraft, and Michael J Vellekoop. A highly uniform lamination micromixer with wedge shaped inlet channels for time resolved infrared spectroscopy. 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Droplet actuation induced by coalescence: experimental evidences and phenomenological modeling

This paper considers the interaction between two droplets placed on a substrate in immediate vicinity. We show here that when the two droplets are of different fluids and especially when one of the droplet is highly volatile, a wealth of fascinating phenomena can be observed. In particular, the interaction may result in the actuation of the droplet system, i.e. its displacement over a finite length. In order to control this displacement, we consider droplets confined on a hydrophilic stripe created by plasma-treating a PDMS substrate. This controlled actuation opens up unexplored opportunities in the field of microfluidics. In order to explain the observed actuation phenomenon, we propose a simple phenomenological model based on Newton's second law and a simple balance between the driving force arising from surface energy gradients and the viscous resistive force. This simple model is able to reproduce qualitatively and quantitatively the observed droplet dynamics