[Transferts thermiques lors de lʼimpact de goutte sur une paroi en régime de Leidenfrost]
Les phénomènes dʼinteractions gouttes/paroi jouent un rôle important dans les chambres de combustion des turboréacteurs. Ils participent notamment à la production et au mélange de la vapeur de combustible ainsi quʼaux transferts de chaleur en paroi. Différents régimes dʼimpact peuvent être observés selon les conditions : le rebond, lʼéclatement avec la formation de gouttes secondaires ainsi que le dépôt dʼun film liquide. La vapeur générée lors de ces interactions migre ensuite vers lʼintérieur de la chambre de combustion, où la température des gaz est suffisamment élevée pour permettre lʼinflammation. Cette étude expérimentale a pour objectif de caractériser les transferts thermiques lors de lʼimpact de gouttelettes dʼeau sur une pastille de Nickel chauffée par induction électromagnétique. La température face-arrière de lʼéchantillon de nickel est mesurée à lʼaide dʼune caméra infrarouge, et le flux extrait à la paroi est estimé par un modèle dʼinversion semi-analytique tenant compte de la conduction dans la pastille ainsi que des pertes convective et radiative. En parallèle, lʼéchauffement des gouttes est caractérisé à lʼaide de la fluorescence induite par laser à deux couleurs. Cette technique a été récemment étendue à de lʼimagerie dans le cadre de cette étude. Elle permet dʼestimer la chaleur sensible gagnée par les gouttes lors de lʼimpact. La paroi est maintenue à une température supérieure à la température de Leidenfrost, tandis que le nombre de Weber des gouttes incidentes est modifié de manière à obtenir des rebonds et des éclatements. La comparaison entre la chaleur sensible gagnée par les gouttes et le flux extrait à la paroi permet finalement dʼévaluer le flux de chaleur prélevée par évaporation. Les contributions au refroidissement de ces flux varient de manière significative en fonction du diamètre des gouttes, mais aussi du nombre de Weber des gouttes incidentes.
In aero-engines, droplet/wall interaction phenomena have a considerable influence on the mixture formation process and on wall heat fluxes. Impinging droplets may rebound, splash into secondary droplets or form a liquid film onto the solid surface. Droplet rebound and splashing is also a mechanism for the back penetration of the fuel vapor in the central region of the combustion chamber where the gas temperature is high enough for ignition. This work is an experimental study aiming at characterizing the heat transfers induced by the impingement of water droplets (diameter 80–180 μm) on a thin nickel plate heated by electromagnetic induction. The temperature of the rear face of the nickel sample is measured by means of an infrared camera and the heat removed from the wall due to the presence of the droplets is estimated using a semi-analytical inverse heat conduction model. In parallel, the temperature of the droplets is measured using the two-color Laser-Induced Fluorescence Thermometry which has been extended to imagery for the purpose of these experiments. The measurements of the variation in the droplet temperature occurring during an impact allow determining the liquid sensible heat. Measurements are performed at surface conditions well above the Leidenfrost temperature. A wide range of Weber numbers corresponding to the bouncing and splashing regimes are tested. Comparison between the heat flux removed from the wall and the sensible heat gained by the liquid allows estimating the heat flux related to liquid evaporation. Results reveal that the respective level of the droplet sensible heat and the heat lost due to liquid vaporization can vary significantly with the droplet sizes and the Weber number.
Mot clés : Impact de gouttes, Paroi chaude, Leidenfrost, Fluorescence induite par Laser, Transferts thermiques
@article{CRMECA_2013__341_1-2_75_0,
author = {Pierre Dunand and Guillaume Castanet and Michel Gradeck and Fabrice Lemoine and Denis Maillet},
title = {Heat transfer of droplets impinging onto a wall above the {Leidenfrost} temperature},
journal = {Comptes Rendus. M\'ecanique},
pages = {75--87},
publisher = {Elsevier},
volume = {341},
number = {1-2},
year = {2013},
doi = {10.1016/j.crme.2012.11.006},
language = {en},
}
TY - JOUR AU - Pierre Dunand AU - Guillaume Castanet AU - Michel Gradeck AU - Fabrice Lemoine AU - Denis Maillet TI - Heat transfer of droplets impinging onto a wall above the Leidenfrost temperature JO - Comptes Rendus. Mécanique PY - 2013 SP - 75 EP - 87 VL - 341 IS - 1-2 PB - Elsevier DO - 10.1016/j.crme.2012.11.006 LA - en ID - CRMECA_2013__341_1-2_75_0 ER -
%0 Journal Article %A Pierre Dunand %A Guillaume Castanet %A Michel Gradeck %A Fabrice Lemoine %A Denis Maillet %T Heat transfer of droplets impinging onto a wall above the Leidenfrost temperature %J Comptes Rendus. Mécanique %D 2013 %P 75-87 %V 341 %N 1-2 %I Elsevier %R 10.1016/j.crme.2012.11.006 %G en %F CRMECA_2013__341_1-2_75_0
Pierre Dunand; Guillaume Castanet; Michel Gradeck; Fabrice Lemoine; Denis Maillet. Heat transfer of droplets impinging onto a wall above the Leidenfrost temperature. Comptes Rendus. Mécanique, Volume 341 (2013) no. 1-2, pp. 75-87. doi : 10.1016/j.crme.2012.11.006. https://comptes-rendus.academie-sciences.fr/mecanique/articles/10.1016/j.crme.2012.11.006/
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