Vanishing of bubble entrapment below an impacting boiling liquid droplet

While the impact of a droplet onto a surface in air is an extensively studied problem, the impact of liquids in thermodynamic equilibrium with their own vapor (i.e., boiling liquids) remains largely unexplored. These types of impacts are precisely what is encountered during transport of cryogenic liquids, where sloshing wave impact is responsible for most of the dynamical load experienced by the containing structure. For this work we have developed an experimental setup to generate Novec 7000 droplets surrounded by their own vapor and observe their impact upon a sapphire surface. Whereas in air it is well known that during impact, under ambient conditions, a liquid droplet will entrap an air bubble, our experiments show that, close to room temperature, a Novec 7000 droplet will entrap a bubble when surrounded by air, but not when surrounded by its own vapor. However, when the impact surface is heated, vapor entrapment will occur. We present results at different impact velocities and surface temperatures to create a phase diagram of the occurrence of vapor bubble entrapment.