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mardi 24 mai — 14:00

Molecular Dynamic study of heterogeneous nucleation in liquid

Julien Morthomas (Laboratoire de Physique de la Matière Condensée et Nanostructures, Lyon)

par Pierre Pujol - 24 mai 2011

The mechanism of heterogeneous bubbles nucleation in liquid near a hot solid wall has received much attention those last decades. Experimentally the first goal is to design the surface of the solid in order to maximize its heat loss, or heat flux, trough the formation and detachment of vapor bubbles : the boiling heat transfer. Recently, thermal physicists have observed that the nanostructure of the solid surface can increase or decrease the transferred heat flux. However at this scale it is impossible to visualize nano-bubbles eventually created along nano-heterogeneities present on the solid.

Molecular Dynamic simulations (MD) can overcome this scale difficulty. We propose here to present Molecular Dynamic results on the nucleation of nano-vapor bubbles in Lennard-Jones liquid implied by and near a hot solid. At first we are interested on the dynamic process of nano-bubbles formation along a plane wall. We discuss the critical volume of bubbles, the evolution in time of bubbles size, the geometry of the bubbles in function of the solid attraction or wettability and the phenomenon of bubbles coalescence. At second we have simulated and observed the dynamic process of vapor bubble nucleation near nanometer scale geometric cavities or defaults along the solid. In particularly we have studied the role of the form of cavities, closed or opened indentations and too the influence of the solid wettability. Finally we are able to extract in all our MD simulations temperature and heat flux profiles around bubbles and the solid in order to argument the influence of the nanostructure on the boiling heat transfer at the nanoscale.