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| Dynamics of impacting droplets |
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 Background
Spray and droplet impingement onto heated walls occur in a wide range of technological applications. The study of single droplet impact provides the knowledge of the physical processes involved, which is required to model spray and droplet wall interaction. Fuel injection, which motivated the beginning of this investigation, is among the applications demanding the most from the aptitude to accurately describe the physics of interaction. In this context, two crucial issues need to be addressed: the ability to predict the dynamic regime occurring under given impact conditions and the ability to predict quantitatively the characteristics of the secondary atomization, which will affect the fuel/air mixture and consequently the engine performance.
As the surface is heated above the ambient temperature, heat is transferred to the impacting droplet altering the fluid-dynamic behaviour in a way that depends on the ratio of the time scale associated with the heat transfer with the time scale associated with momentum transfer. So, the droplet will exhibit quite different behaviour as it falls within the various boiling regimes:
i) Cold-surface/evaporation regime, Twall<Tsaturation: (movie)
ii) Nucleate boiling regime, Tsaturation <Twall<TCritical Heat Flux: (movie)
iii) Transition regime, TCritical Heat Flux <Twall<TLeidenfrost: (movie)
iv) Film boiling regime, Twall>TLeidenfrost: small Weber number (movie)
moderate Weber number (movie)
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