| Wed October 12th 2011 16:00 ZH286 | Seminar | 1. Faraday waves and their transition to jetting 2. Droplet impact on superheated surfaces Erik-Jan Staat, Ivan van der Kroon |
Details:ABOUT 1: Faraday waves and their transition to jetting.Faraday instabilities arise from specific parametric excitation of oscillatory systems and are attributed to Micheal Faraday for his appendix to an 1831 Phil.Trans.-paper "On the forms and states assumed by fluids in contact with vibrating elastic surfaces". These instabilities appear in many fields and most of you might also remember the Journal Club "Walking and orbiting droplets". This seminar I will talk about Faraday instabilities for free surfaces waves in a vertically vibrating cylinder. The system's parameters are chosen around the axis-symmetric harmonic state. Due to self-focusing of the inertial energy, finite-time singularities occur even at moderate driving amplitudes, i.e. the standing wave will grow gradually until it forms a cavity in the fluid which creates an upward jet upon collapse. ABOUT 2: Droplet impact on superheated surfaces During impact of a liquid droplet on a surface heated above the liquid's boiling point, unexpected outcomes may happen. Despite the long history of work on this subject, the precise roles of the impact conditions on the formation of the Leidenfrost layer is still unknown. We have experimentally determined the conditions under which impact behaviors of different regimes can be realized. We show that the maximum deformation of impacting droplets on surfaces in film boiling regimes depends on the Weber number in a universal way regardless of the surface temperature and of liquid properties being used. Our results underscore the universality of impact behaviors in the film boiling regimes and may help elucidate the roles of different effects involved in interactions between liquid droplets and heated surfaces. | ||
