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Café thésard : Droplet impact on superheated surfaces
2 juillet 2021 @ 14h00 - 15h30
Le prochain café thésard sera présenté vendredi 2 juillet à 14h par Abhishek Srivastava, doctorant de l’équipe Tansfert dans les fluides du LEMTA. Il aura lieu à distance par Microsoft Teams en cliquant sur ce lien.
Résumé :
Heat transfer is a vital phenomenon which needs to be understood well to solve the problems of rapid high heat removal in mechanical, electrical and electronic applications such as nuclear chambers, combustion, computer devices. Most of the processes of heat removal include air cooling and some use recirculation of water and spray cooling. Out of these spray cooling is a popular method of heat removal as it gives several added advantages, one being the low volume of coolant used. However, it is still difficult to obtain the physical understanding of the boiling process which the fluid undergoes during the drop impact, droplet dynamics of the different fluids, control of heat flux from the solid surface until the fluid evaporates. There is a need to study it at a fundamental level using efficient optical techniques to observe the temperature fields and to propose a model to determine the heat flux.
In the current PhD project, study of heat transfer phenomenon is done for a single droplet impact on a superheated surface. When a droplet of fluid impacts on a superheated surface, it undergoes different phenomenon’s which depend on several factors such as Weber number, surface temperature etc. A droplet can evaporate, bounce back, split into several smaller droplets; spread, create a film of vapor etc. when it contacts a hot surface. To study these droplet dynamics, shadowgraphy technique is used which involves image capture using a High-speed camera. To observe the cooling of the heated surface (sapphire with a black micro meter coating of TiAln) after the drop contacts the surface is done using an Infrared camera and calculation of the cooling temperature with an inverse heat conduction method. Finally, to observe the heating inside the droplet, two color planar laser induced fluorescence technique (2cLIF) is used which involves image capture of the temperature field of the droplet resolved both spatially and temporally.
In the presentation, I will be explaining these techniques, their working principle, how are they used in the experiment, the experimental setup and also cover some topics related to the measurement techniques which are important to the accuracy of the experiment.