23 research outputs found
Elaboration d'une loi d'Ă©change convectif dans le cas d'une compression d'air par piston liquide
Ces travaux portent sur la mise au point d'une corrélation d'échange convectif adaptée à la compression quasi isotherme d'air par piston liquide. Cet échange thermique entre l'air et les parois de la chambre de compression est déterminant pour limiter l'élévation de la température de l'air au cours de la compression et ainsi se rapprocher de l'isothermicité. La recherche de la corrélation est basée sur une étude dimensionnelle du systÚme complétée par un ensemble de mesures effectuées sur un banc d'essai. Un travail d'optimisation est ensuite réalisé pour déterminer les valeurs des coefficients de cette corrélation permettant de reproduire le plus fidÚlement possible l'évolution de l'échange thermique dans la chambre de compression
Functions of the Nonsense-Mediated mRNA Decay Pathway in Drosophila Development
Nonsense-mediated mRNA decay (NMD) is a cellular surveillance mechanism that degrades transcripts containing premature translation termination codons, and it also influences expression of certain wild-type transcripts. Although the biochemical mechanisms of NMD have been studied intensively, its developmental functions and importance are less clear. Here, we describe the isolation and characterization of Drosophila âphotoshopâ mutations, which increase expression of green fluorescent protein and other transgenes. Mapping and molecular analyses show that photoshop mutations are loss-of-function mutations in the Drosophila homologs of NMD genes Upf1, Upf2, and Smg1. We find that Upf1 and Upf2 are broadly active during development, and they are required for NMD as well as for proper expression of dozens of wild-type genes during development and for larval viability. Genetic mosaic analysis shows that Upf1 and Upf2 are required for growth and/or survival of imaginal cell clones, but this defect can be overcome if surrounding wild-type cells are eliminated. By contrast, we find that the PI3K-related kinase Smg1 potentiates but is not required for NMD or for viability, implying that the Upf1 phosphorylation cycle that is required for mammalian and Caenorhabditis elegans NMD has a more limited role during Drosophila development. Finally, we show that the SV40 3âČ UTR, present in many Drosophila transgenes, targets the transgenes for regulation by the NMD pathway. The results establish that the Drosophila NMD pathway is broadly active and essential for development, and one critical function of the pathway is to endow proliferating imaginal cells with a competitive growth advantage that prevents them from being overtaken by other proliferating cells
Experimental study and modeling of near isothermal air compression for offshore energy storage device
Le stockage dâĂ©nergie par air comprimĂ© est une des technologies nĂ©cessaires Ă lâemploi massif des Ă©nergies renouvelables intermittentes, dâorigine solaire ou Ă©olienne. La compression dâair par piston liquide permet dâaugmenter lâefficacitĂ© du stockage dâĂ©nergie en favorisant un Ă©change thermique intense dans la chambre de compression. La description et lâĂ©valuation de cet Ă©change convectif pour des chambres de compression Ă faible rapport alĂ©sage/course ne sont cependant que peu Ă©tudiĂ©es dans la littĂ©rature scientifique. A lâaide dâune Ă©tude expĂ©rimentale menĂ©e sur deux bancs dâessais, lâĂ©change convectif interne dans la chambre de compression est Ă©tudiĂ©. Une mĂ©thode inverse, couplĂ©e Ă la mesure de la tempĂ©rature de lâair comprimĂ© et de la position du piston, est employĂ©e afin de dĂ©terminer les transferts thermiques pariĂ©taux instantanĂ©s au cours des compressions.AprĂšs avoir mis en lumiĂšre la prĂ©sence systĂ©matique dâune transition du rĂ©gime convectif de type laminaire vers un rĂ©gime turbulent dans le volume dâair comprimĂ©, de nouvelles corrĂ©lations dâĂ©change convectif sont recherchĂ©es. Sur la base de 73 expĂ©rimentations, plusieurs formes de corrĂ©lations basĂ©es sur des nombres sans dimension sont optimisĂ©es puis comparĂ©es. Deux nouvelles corrĂ©lations du nombre de Nusselt, lâune en rĂ©gime laminaire et lâautre en rĂ©gime turbulent, sont ensuite sĂ©lectionnĂ©es. Un modĂšle instationnaire thermodynamique 1D de la chambre de compression est alors construit dans lâenvironnement Matlab / Simulink afin de tester la qualitĂ© de ces corrĂ©lations. Les rĂ©sultats numĂ©riques sont ainsi comparĂ©s aux donnĂ©es expĂ©rimentales. Finalement, deux essais expĂ©rimentaux supplĂ©mentaires, rĂ©alisĂ©s sur un banc dâessai diffĂ©rent, permettent de confirmer la qualitĂ© des nouvelles corrĂ©lations dâĂ©change convectif proposĂ©es.Energy storage by compressed air would be one of the required technologies for enabling massive use of intermittent solar or wind renewable energy sources. Air compression using a liquid piston enables an increase in the energy storage efficiency by inducing an intense heat exchange in the compression chamber. Few studies reported in the literature have focused on the description and evaluation of the convective heat exchange for a low ratio compression chamber (L/D). Using an experimental study and two test benches, the internal convective heat transfer during compression has been studied. In addition to measuring liquid piston position and air pressure, an inverse method was used to determine the instantaneous parietal convective heat flow during compression. After highlighting the presence of a systematic transition from laminar to turbulent convective regime in the compressed air, new convective heat transfer correlations were sought. On the basis of 73 experiments, several correlation forms based on dimensionless numbers were optimized and compared. Two new Nusselt number correlations, one for laminar and the other for turbulent flow, were then selected. A 1D thermodynamic transient model of the compression chamber was built using Matlab / Simulink environment in order to test the quality of these correlations. Thus, numerical results and experimental data were compared. Finally, results from two additional experiments carried out on a different test bench have confirmed the quality of the new proposed correlations for convective heat exchange
Etude expĂ©rimentale et modĂ©lisation de la compression quasi isotherme dâair pour le stockage dâĂ©nergie en mer
Energy storage by compressed air would be one of the required technologies for enabling massive use of intermittent solar or wind renewable energy sources. Air compression using a liquid piston enables an increase in the energy storage efficiency by inducing an intense heat exchange in the compression chamber. Few studies reported in the literature have focused on the description and evaluation of the convective heat exchange for a low ratio compression chamber (L/D). Using an experimental study and two test benches, the internal convective heat transfer during compression has been studied. In addition to measuring liquid piston position and air pressure, an inverse method was used to determine the instantaneous parietal convective heat flow during compression. After highlighting the presence of a systematic transition from laminar to turbulent convective regime in the compressed air, new convective heat transfer correlations were sought. On the basis of 73 experiments, several correlation forms based on dimensionless numbers were optimized and compared. Two new Nusselt number correlations, one for laminar and the other for turbulent flow, were then selected. A 1D thermodynamic transient model of the compression chamber was built using Matlab / Simulink environment in order to test the quality of these correlations. Thus, numerical results and experimental data were compared. Finally, results from two additional experiments carried out on a different test bench have confirmed the quality of the new proposed correlations for convective heat exchange.Le stockage dâĂ©nergie par air comprimĂ© est une des technologies nĂ©cessaires Ă lâemploi massif des Ă©nergies renouvelables intermittentes, dâorigine solaire ou Ă©olienne. La compression dâair par piston liquide permet dâaugmenter lâefficacitĂ© du stockage dâĂ©nergie en favorisant un Ă©change thermique intense dans la chambre de compression. La description et lâĂ©valuation de cet Ă©change convectif pour des chambres de compression Ă faible rapport alĂ©sage/course ne sont cependant que peu Ă©tudiĂ©es dans la littĂ©rature scientifique. A lâaide dâune Ă©tude expĂ©rimentale menĂ©e sur deux bancs dâessais, lâĂ©change convectif interne dans la chambre de compression est Ă©tudiĂ©. Une mĂ©thode inverse, couplĂ©e Ă la mesure de la tempĂ©rature de lâair comprimĂ© et de la position du piston, est employĂ©e afin de dĂ©terminer les transferts thermiques pariĂ©taux instantanĂ©s au cours des compressions.AprĂšs avoir mis en lumiĂšre la prĂ©sence systĂ©matique dâune transition du rĂ©gime convectif de type laminaire vers un rĂ©gime turbulent dans le volume dâair comprimĂ©, de nouvelles corrĂ©lations dâĂ©change convectif sont recherchĂ©es. Sur la base de 73 expĂ©rimentations, plusieurs formes de corrĂ©lations basĂ©es sur des nombres sans dimension sont optimisĂ©es puis comparĂ©es. Deux nouvelles corrĂ©lations du nombre de Nusselt, lâune en rĂ©gime laminaire et lâautre en rĂ©gime turbulent, sont ensuite sĂ©lectionnĂ©es. Un modĂšle instationnaire thermodynamique 1D de la chambre de compression est alors construit dans lâenvironnement Matlab / Simulink afin de tester la qualitĂ© de ces corrĂ©lations. Les rĂ©sultats numĂ©riques sont ainsi comparĂ©s aux donnĂ©es expĂ©rimentales. Finalement, deux essais expĂ©rimentaux supplĂ©mentaires, rĂ©alisĂ©s sur un banc dâessai diffĂ©rent, permettent de confirmer la qualitĂ© des nouvelles corrĂ©lations dâĂ©change convectif proposĂ©es
Méthode VOF pour la simulation numérique de l'écoulement de l'air comprimé et du transfert thermique associé dans un piston liquide
National audienceThis study focuses on 2D modeling of a process of air compression in a liquid piston. In order to study this flow numerically, the choice was made to use the VOF (Volume of Fluid) method which is adapted to this type of flow. The flow regime switchs from laminar to transient, so the LES (Large Eddy Simulation) method was chosen for turbulence modeling. We tried to get closer to the experimental results and to better illustrate the different physical phenomena present during the compression using different approaches.Cette étude porte sur la modélisation 2D d'un processus de compression d'air dans un piston liquide. Afin d'étudier numériquement cet écoulement, le choix a porté sur l'utilisation de la méthode VOF (Volume of Fluid) qui est adaptée à ce type d'écoulement. Le régime de l'écoulement varie au cours du processus de compression passant de laminaire à transitoire puis turbulent, ainsi la méthode LES (Large Eddy Simulation) a été choisie pour la modélisation de la turbulence. Des améliorations ont été apportées afin de s'approcher des résultats expérimentaux obtenus précédemment et de mieux illustrer les différents phénomÚnes physiques présents lors de la compression
Méthode VOF pour la simulation numérique de l'écoulement de l'air comprimé et du transfert thermique associé dans un piston liquide
National audienceThis study focuses on 2D modeling of a process of air compression in a liquid piston. In order to study this flow numerically, the choice was made to use the VOF (Volume of Fluid) method which is adapted to this type of flow. The flow regime switchs from laminar to transient, so the LES (Large Eddy Simulation) method was chosen for turbulence modeling. We tried to get closer to the experimental results and to better illustrate the different physical phenomena present during the compression using different approaches.Cette étude porte sur la modélisation 2D d'un processus de compression d'air dans un piston liquide. Afin d'étudier numériquement cet écoulement, le choix a porté sur l'utilisation de la méthode VOF (Volume of Fluid) qui est adaptée à ce type d'écoulement. Le régime de l'écoulement varie au cours du processus de compression passant de laminaire à transitoire puis turbulent, ainsi la méthode LES (Large Eddy Simulation) a été choisie pour la modélisation de la turbulence. Des améliorations ont été apportées afin de s'approcher des résultats expérimentaux obtenus précédemment et de mieux illustrer les différents phénomÚnes physiques présents lors de la compression
Underwater CAES assessment: economic and engineering references for energy mix sizing in islands grids
International audienceThis study investigates the system benefits of the integration of an underwater CAES storage technology to support variable renewables integration. The case study is the French island of Guadeloupe, where power specificities are the high share of fossil fuels, i.e. diesel and coal, and the significant seasonal variability of the load. An optimization model is built to test energy scenarios targeting 100% renewables on the island such as to minimize the waste of energy, i.e. the power curtailed, subject to hourly supply-demand balance. The underwater Isothermal-CAES storage system under consideration seems suitable for coupling with large-scale fluctuating energy renewable power plants and to attain carbon emission targets, due to higher efficiency rate (70%) than conventional CAES, and to free of natural gas requirements. The model shows that using I-CAES storage allows the system to avoid curtailment of fluctuating renewables, and that fast adjustment speeds and the resilience to frequent start-ups and shut-downs effects are the suitable features for attaining political energy targets of the island in 2030
Mushroom-shaped bubble plume under bubble crown
International audienceWe study free-rising bubble plumes produced by gas injection in pressurized water to characterize the subsea gas release conditions. Time evolution illustrations of a bubble plume under the chaining regime at atmospheric pressure given above were obtained employing a diffused backlight illumination technique. First, a continuous jet, four times larger than the nozzle diameter, and a large bubble, ten times larger than the nozzle diameter, merge in a mushroom-shaped bubble plume at the jet interruption. Then, the apparition of a new jet enlarges the bubble plume length. The process ends with the mushroom cap detachment while fragmenting into a bubble crown. Question: What is the impact of subsea pressure conditions on the bubble plume evolution up to the sea level surface? The authors gratefully acknowledge France Relance and SEGULA Technologies for funding the project