Influence of the meandering channel geometry on the thermo-hydraulic performances of an intensified heatexchanger/reactor

In the global context of process intensification, heat exchanger/reactors are promising apparatuses to implement exothermic chemical syntheses. However, unlike heat exchange processes, the implementation of chemical syntheses requires to control the residence time to complete the chemistry. A way to combine the laminar regime (i.e. enough residence time) with a plug flow and the intensification of both heat and mass transfers is the corrugation of the reaction path. In this work, the experimental set-up is based on plate heat exchanger/reactor technology. 7 milli channel corrugated geometries varying the corrugation angle, the curvature radius, the developed length, the hydraulic diameter and the aspect ratio have been designed and experimentally characterized (heat transfer, mixing times, pressure drops, RTD). The objectives were to assess their respective performances to derive some correlations depending on the channel design. The results confirmed the benefits of the reaction channel corrugation. Heat and mass transfers have been intensified while maintaining a plug flow behavior in the usually laminar flow regime. Moreover, whatever the meandering channel’s curvature radius, the results highlighted the relevance of considering the Dean number as the scale-up parameter. This dimension less number, more than the Reynolds number, seems to govern the flow in the wavy channels

Le fonctionnement « improvisationnel » de l’enseignant expert

Cet article présente les résultats d'une étude sur la manière dont les enseignants de français conceptualisent les contenus didactiques en fonction des interactions en classe. La représentation qu'ont les enseignants de leur gestion des interactions a été rapportée au moyen de protocoles verbaux concomitants à une tâche de planification et au moyen de protocoles rétrospectifs immédiats. Pour répondre aux réactions des élèves, le fonctionnement fréquemment adopté par l'enseignant semble « improvisationnel ». La planification de l'enseignement est fondée sur des connexions conceptuelles. Elle relie les contenus les uns aux autres selon une appréciation des besoins potentiels des apprenants. Sur le plan cognitif, la planification est la résultante d'une accommodation entre des éléments didactiques organisateurs et les apports potentiellement désorganisateurs du contexte d'interaction. Ces résultats descriptifs corroborent ceux qui ont été obtenus dans d'autres disciplines et acquièrent de ce fait une certaine généralisabilité.This article presents the results of a study of the way teachers of French conceptualize instructional content as related to classroom interaction. Specifically, teacher's perceptions of the management of their interactions was mediated through a verbal report on planning. Improvisation is reported to be a frequent behavior adopted by teachers in their responses to students' reactions. Instructional planning is mostly mental and emphasizes functional connections: content aspects are related to each other according to the needs of students. At the cognitive level, teacher planning seems to be the result of an accomodation between the instructional organizers and the potentially disorganizing aspects of the context. These descriptive results, supported by numerous excerpts, corroborate results noted in other disciplines and thus attain a certain level of generalisability.Este artículo présenta los resultados de un estudio sobre la manera en que los profesores de francés conceptualizan los contenidos didacticos, a partir de las interacciones en la clase. En forma mas especifica, la percepcion que tienen los profesores sobre la gestion de las interacciones fue mediatizada mediante la relacion verbal. Para responder a las reacciones de los alumnos, el funcionamiento frecuentemente adoptado por el profesor parece ser improvisado. La planificacion de la ensenanza es principalmente mental y asociativa: relaciona los contenidos los unos con los otros segun las necesidades de los aprendices. Sobre el piano cognitivo, la planificacion parece ser la résultante de una acomodacion entre los elementos didacticos organizadores y los aportes potencialmente desorganizadores del contexto de interaccion. Estos resultados descriptivos, acompanados de numerosos extractos, corroboran los que han sido obtenidos en otras disciplinas y adquieren, por Io tan to, un caràcter relativamente generalizable.Dieser Artikel präsentiert die Ergebnisse einer Studie iiber die Art, wie die Franzôsisch-Lehrkrâfte die didaktischen Inhalte in Hinsicht auf die Wech- selbeziehungen innerhalb der Klasse erarbeiten. Genauer gesagt, wurde die Idee, die sich die Lehrkrâfte iiber ihre Führung dieser Wechselbeziehungen machen, durch den miind- lichen Bericht zugànglich gemacht. Um auf die Reaktionen der Schüler einzugehen, scheinen die Lehrkrâfte oft den "Improvisationsstil" zu wâhlen. Die Unterrichtsvorbereitung geschieht vor allem im Kopf und durch Assoziationen: sie stellt die Verbindungen zwischen den einzelnen Inhalten entsprechend dem Bedarf der Lernenden her. Auf kognitiver Ebene wird also die Planung zueiner Anpassung der organisatorisch didaktischen Elemente an die moglicherweise auftretenden desorganisierenden Faktoren wâhrend der Interaktion. Diëse beschreibenden Ergebnisse, die durch zahlreiche Zitate aus den Berichten belegt werden, erhärten Funde aus anderen Fächern und kônnen daher in gewisser Weise verallgemeinert werden

Rappel stimulé, objectivation clinique, réflexion partagée. Fondements méthodologiques et applications pratiques de la rétroaction vidéo en recherche et en formation

Cet article1 présente les aspects méthodologiques fondateurs et les considérations pratiques qui ont découlé des usages de la rétroaction vidéo en recherche et en formation. La rétroaction vidéo est désignée en recherche par sa fonction, qui a évolué au fil de trois générations méthodologiques: 1) stimuler le rappel des pensées interactives du sujet; 2) susciter la prise de conscience du sujet; 3) partager la réflexion-sur-l'action. Après un historique du concept de rappel stimulé, l'auteur indique comment les usages de la rétroaction vidéo propres au traitement de l'information ont porté sur la mémoire des pensées interactives puis sur l'« objectivation clinique », puis ont évolué, récemment, vers un usage intégré et réflexif de formation-recherche au sein du paradigme de la pensée des enseignants.This article presents the foundational, methodological aspects of video feedback as well as its practical uses for research and education. In educational research, the kinds of video feedback have been named according to their functions. These functions have evolved overtime. Three methodological functions that match different research goals can be distinguished historically: 1) Stimulate the subjects recall of his/her prior interactive thoughts; 2) Provoke the subjects metacognition and stimulate awareness at the time when the video is reviewed; 3) coconstruct and share, through feedback, the participants' reflections-on-action and promote school change. The author reviews the historical and methodological foundations of these three generations of stimulated recall, clinical interviewing, and shared reflection for change. He demonstrates how the use of video feedback evolved from information-processing towards ethnographies to practical reflection within the paradigms of teacher thinking. Throughout these trends, researchf became education-based, reflective, and teacher-oriented.Este articulo présenta aspectos metodologicos constituyentes y consideraciones prâcticas que resultan del uso de la retroaccion videoscôpica en investigaciôn y en formacion. La retroaccion videoscôpica se define en investigaciôn por su funciôn, la cual ha evolucionado en el transcurso de très generaciones metodologicas: 1) estimular el recuerdo de pensamientos interactivos del sujeto, 2) suscitar la concientizaciôn del sujeto, 3) comparer la reflexion en accion. Después de una breve historia del concepto de recuerdo estimulado, el autor indica cômo el uso de la retroaccion videoscôpica propio al tratamiento de la informaciôn pronto se dedico a la objetivaciôn clinica y después evoluciono, mas recientemente, hacia un uso integrado y reflexivo en formacion-investigacion dentro del paradigma del pensimiento de los docentes.Dieser Artikel beschreibt die grundliegenden methodologischen Aspekte und die praktischen Erwàgungen, die die in Forschung und Ausbildung ûbliche Verwertung des Video-Feedbacks nach sich gezogen hat. Die Funktion des Video-Feedbacks hat sich im Laufe von drei methodologischen Generationen entwickelt: 1) die Erinnerung an die interaktiven Gedanken des Forschungsteilnehmers stimulieren; 2) dem Forschungsteilnehmer ein Bewufo- werden ermoglichen; 3) ùber das Handeln Ûberlegungen anstellen und mit anderen teilen. Nach einer geschichtlichen Darstellung des BegrifTs der stimulierten Erinnerung zeigt der Verfasser, wie man sich bei der Verwertung des Video-Feedbacks als Teil der Informations- verarbeitung zunâchst mit den gespeicherten interaktiven Gedanken, dann mit der "klinischen Objektivation" beschàftigt hat, um sich schliefêlich einer ganzheitlichen Verwertung in einer Ausbildungs- und Forschungsperspektive innerhalb des Paradigmas des Denkens der Lehrer zuzuwenden

Unmixing-based gas plume tracking in LWIR hyperspectral video sequences

International audienceIt is now possible to collect hyperspectral video sequences (HVS) at a near real-time frame rate. The wealth of spectral , spatial and temporal information of those sequences is particularly appealing for chemical gas plume tracking. Existing state-of-the-art methods for such applications however produce only a binary information regarding the position and shape of the gas plume in the HVS. Here, we introduce a novel method relying on spectral unmixing considerations to perform chemical gas plume tracking, which provides information related to the gas plume concentration in addition to its spatial localization. The proposed approach is validated and compared with three state-of-the-art methods on a real HVS

Segmentation hiérarchique d'images multimodales

National audienceHierarchies of partitions are widely used in the context of image segmentation. However,in the case of multimodal images, the fusion of multiple hierarchies remains a challenge. Recently, braids of partitions have been proposed as a possible solution to this issue, but have never been implemented in a practical case.In this paper, we propose a new methodology to achieve multimodal segmentation, based on this notion of braids of partitions. This new method is applied in a practical case, namely the joint segmentation of hyperspectral and LiDAR data. Obtained results confirm the potential of the proposed method.Les hiérarchies de partitions sont couramment utilisées pour segmentation d'images. Dans le cas d'images multimodales toutefois, la fusion de plusieurs hiérarchies reste un problème. Récemment, les tresses de partitions ont été proposées comme une possible solution à ce problème, mais n'ont jamais été implémentées dans un cas pratique. Nous proposons ainsi une nouvelle méthodologie, basée sur cette notion de tresse de partitions, pour effectuer la segmentation d'images multimodales. Cette méthode est appliquée dans un cas concret, à savoir la segmentation conjointe de données hyperspectrales et LiDAR. Les résultats obtenus confirment le potentiel de la méthode proposée

From local to global unmixing of hyperspectral images to reveal spectral variability

International audienceThe linear mixing model is widely assumed when unmixing hyperspectral images, but it cannot account for endmembers spectral variability. Thus, several workarounds have arisen in the hyperspectral unmixing literature, such as the extended linear mixing model (ELMM), which authorizes endmembers to vary pixelwise according to scaling factors, or local spectral unmixing (LSU) where the unmixing process is conducted locally within the image. In the latter case however, results are difficult to interpret at the whole image scale. In this work, we propose to analyze the local results of LSU within the ELMM framework, and show that it not only allows to reconstruct global endmembers and fractional abundances from the local ones, but it also gives access to the scaling factors advocated by the ELMM. Results obtained on a real hyperspectral image confirm the soundness of the proposed methodology

Segmentation of Multimodal Images based on Hierarchies of Partitions

International audienceHierarchies of partitions are widely used in the context of image segmentation, but when it comes to multimodal images, the fusion of multiple hierarchies remains a challenge. Recently, braids of partitions have been proposed as a possible solution to this issue, but have never been implemented in a practical case. In this paper, we propose a new methodology to achieve multimodal segmentation based on this notion of braids of partitions. We apply this new method in a practical example, namely the segmentation of hyperspectral and LiDAR data. Obtained results confirm the potential of the proposed method

Hyperspectral Image Segmentation Using a New Spectral Unmixing-Based Binary Partition Tree Representation

International audienceThe Binary Partition Tree (BPT) is a hierarchical region-based representation of an image in a tree structure. BPT allows users to explore the image at different segmentation scales. Often, the tree is pruned to get a more compact representation and so the remaining nodes conform an optimal partition for some given task. Here, we propose a novel BPT construction approach and pruning strategy for hyperspectral images based on spectral unmixing concepts. Linear Spectral Unmixing (LSU) consists of finding the spectral signatures of the materials present in the image (endmembers) and their fractional abundances within each pixel. The proposed methodology exploits the local unmixing of the regions to find the partition achieving a global minimum reconstruction error. Results are presented on real hyperspectral data sets with different contexts and resolutions

Gas Plume Detection and Tracking in Hyperspectral Video Sequences using Binary Partition Trees

International audienceThanks to the fast development of sensors, it is now possible to acquire sequences of hyperspectral images. Those hyperspectral video sequences are particularly suited for the detection and tracking of chemical gas plumes. However, the processing of this new type of video sequences with the additional spectral diversity, is challenging and requires the design of advanced image processing algorithms. In this paper, we present a novel method for the segmentation and tracking of a chemical gas plume diffusing in the atmosphere, recorded in a hyperspectral video sequence. In the proposed framework, the position of the plume is first estimated, using the temporal redundancy of two consecutive frames. Second, a Binary Partition Tree is built and pruned according to the previous estimate, in order to retrieve the real location and extent of the plume in the frame. The proposed method is validated on a real hyperspectral video sequence and compared with a state-of-the-art method

RAPIC project: toward a new generation of inexpensive heat exchanger-reactors for process intensification

Process intensification (PI) in chemical production is a major concern of chemical manufacturers. This alternative technology involves transposing syntheses into continuous plug flow reactors with process intensification, leading to a multifunctional heat exchanger-reactor. In this context, the RAPIC R&D project aims to develop an innovative low-cost component (in the 10 kg/hour range). This project deals with the design from the local to the global scale and with testing, from elementary mock-ups to pilot scale. The present paper gives a detailed description of this research project and presents the main results on specification and definition of the reaction channel and the first simple mock-ups