Isotropic and anisotropic heat transfer in active wall porous media foam type

Positive buildings in energy are, nowadays, a recurrent objective of many researches in the construction and energetic efficiency domain. Furthermore, to achieve this objective, some studies about active and reactive walls have been carried out employing porous medium as a main structure. Nevertheless, transfer characterization in a foam type sample is not fully understood. The goal of this study is to improve the characterization of heat transfer in isotropic and anisotropic configurations of a porous medium. Thus, a finite volume method was implemented to study a heat transfer through these media, in the interest of achieving their ratio equivalent to fluid thermal conductivity (i.e. Nusselt number). Finally, the results indicate a notable influence of the ratio of the contact and the total inlet area on the isotropic configuration as well as strong influence given by the different axis on the anisotropic model. Moreover, the analysis shows that in an active wall constituted by two solid phases, these effects will be preponderant for their characterization.Comment: 18\`eme Journ\'ees Internationales de Thermique (JITH 2017), Oct 2017, Monastir, Tunisi

Teaching Fluid Mechanics for Undergraduate Students in Applied Industrial Biology: from Theory to Atypical Experiments

EBI is a further education establishment which provides education in applied industrial biology at level of MSc engineering degree. Fluid mechanics at EBI was considered by students as difficult who seemed somewhat unmotivated. In order to motivate them, we applied a new play-based pedagogy. Students were asked to draw inspiration from everyday life situations to find applications of fluid mechanics and to do experiments to verify and validate some theoretical results obtained in course. In this paper, we present an innovative teaching/learning pedagogy which includes the concept of learning through play and its implications in fluid mechanics for engineering. Examples of atypical experiments in fluid mechanics made by students are presented. Based on teaching evaluation by students, it is possible to know how students feel the course. The effectiveness of this approach to motivate students is presented through an analysis of students' teaching assessment. Learning through play proved a great success in fluid mechanics where course evaluations increased substantially. Fluid mechanics has been progressively perceived as interesting, useful, pleasant and easy to assimilate. It is shown that this pedagogy which includes educational gaming presents benefits for students. These experiments seem therefore to be a very effective tool for improving teaching/learning activities in higher education

Séparation des constituants d'un fluide binaire remplissant une cavité horizontale soumise à des flux croisés de chaleur

On étudie numériquement et analytiquement l'influence de l'effet Soret sur la séparation des espèces d'un mélange binaire confiné dans une enceinte parallélépipédique horizontale soumise à des flux de chaleur uniformes et croisés. L'écoulement unicellulaire induit par le flux de chaleur latéral peut conduire à une importante séparation des espèces. L'hypothèse d'écoulement parallèle est utilisée pour déterminer la solution analytique associée à l'écoulement de double diffusion unicellulaire. Le problème étudié en plus de l'allongement, dépend de cinq nombres adimensionnels qui sont les nombres de Rayleigh, de Prandtl,le facteur de séparation, le nombre de Lewis et le rapport des densités horizontale et verticale de flux. Les applications numériques choisies correspondent au mélange binaire d'eau (60%) et d'éthanol (40%). Les résultats analytiques sont corroborés par ceux obtenus par des simulations numériques directes

Analyse de l'écoulement de Poiseuille - Rayleigh - Bénard (PRB) par la méthode de Lattice Boltzmann

International audienceUne méthode numérique basée sur l'équation de Boltzmann (LBE) à deux distributions est développée pour résoudre les équations de conservation (énergie et quantité de mouvement). La configuration considérée est un canal chauffé par le bas, refroidi par le haut et traversé par un fluide (Pr = 1). L'étude est effectuée pour une gamme de nombres de Rayleigh (

Analyse de la stabilité linéaire des solutions de double diffusion pure et de convection obtenues dans le cas d'une cavité poreuse, horizontale, saturée par un fluide binaire soumise à des flux thermiques croisés

La convection thermogravitationnelle, qui génère des variations locales de la masse volumique du fluide en fonction de la température, conduit finalement à une séparation des espèces dans la cavité. On s'intéresse dans ce travail à la séparation des espèces d'une solution binaire remplissant une cavité parallélépipédique poreuse, placée dans le champ de la pesanteur, et soumise au niveau de ses parois horizontales et verticales à des densités de flux uniformes et croisés. Nous déterminons aussi les paramètres de contrôle conduisant à la séparation optimale, En utilisant l'étude de la stabilité linéaire, on a vérifié que le nombre de Rayleigh critique linéaire, , associé à la perte de la stabilité de la solution unicellulaire est supérieur au nombre de Rayleigh optimal, , conduisant à la séparation des constituants du mélange

Coalescence of surfactant-laden droplets

Droplet coalescence is an important process in nature and various technologies (e.g. inkjet printing). Here, we unveil the surfactant mass-transport mechanism and report on several major differences in the coalescence of surfactant-laden droplets as compared to pure water droplets by means of molecular dynamics simulation of a coarse-grained model. Large scale changes to bridge growth dynamics are identified, such as the lack of multiple thermally excited precursors, attenuated collective excitations after contact, slowing down in the inertial regime due to aggregate-induced rigidity and reduced water flow, and a slowing down in the coalescence rate (deceleration) when surfactant concentration increases, while at the same time we also confirm the existence of an initial thermal, and a power-law, inertial, regime of the bridge growth dynamics in both the pure and the surfactant-laden droplets. Thus, we unveil the key mechanisms in one of the fundamental topological processes of liquid droplets containing surfactant, which is crucial in relevant technologies.Comment: 23 pages, 7 figure

Heterogeneous nanofluids: natural convection heat transfer enhancement

Convective heat transfer using different nanofluid types is investigated. The domain is differentially heated and nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach. The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration but remains less than the enhancement previously underlined in forced convection case

A batteryless temperature sensor based on high temperature sensitive material

The original publication is available at www.epjap.orgThe major challenge in wireless sensor networks is the reduction of energy consumption. Passive wireless sensor network is an attractive solution for measuring physical parameters in harsh environment for large range of applications requiring sensing devices with low cost of fabrication, small size and long term measurement stability. Batteryless temperature sensing techniques are an active research field. The approach developed in our work holds a promising future for temperature sensor applications in order to successfully reduce the energy consumption. The temperature sensor presented in this paper is based on the electromagnetic transduction principle using the integration of the high temperature sensitive material into a passive structure. Variation in temperature makes the dielectric constant of this material changing, and such modification induces variation in the resonant frequencies of high-Q whispering-gallery modes (WGM) in the millimeter-wave frequency range. Following the results achieved, the proposed device shows a linear response to the increasing temperature and these variations can be remotely detected from a radar interrogation.This research was supported in part by EMMAG Program, 2014, funded by the European Commission.Bakkali, A.; Pelegrí Sebastiá, J.; Laghmich, Y.; Lyhyaoui, A. (2016). A batteryless temperature sensor based on high temperature sensitive material. European Physical Journal: Applied Physics. 74(2). doi:10.1051/epjap/2015150376S2460674