Dynamics of disc impact onto a boiling liquid: effect of phase change*

The dynamics of disc impact onto a boiling liquid, i.e., a liquid that is in thermodynamic equilibrium with its vapour phase, differs from that on water at ambient air conditions. The key distinction lies in that the entrapped gas pocket beneath the disc contains a condensable vapour which can undergo a phase change due to energy exchange with the surrounding liquid during impact. In this study, we demonstrate that at high impact velocity and low ambient temperature, the entrapped vapour pocket under a circular flat disc collapses rapidly upon impact, resulting in exceptionally high impact pressure at the disc centre. We rationalise this effect as a result of the condensation of the vapour pocket due to compression upon impact. We show that the impact velocity and the vapour density, which changes with the ambient temperature, determine the condensation rate and the subsequent contraction of the vapour pocket. Additionally, by increasing the temperature of the impacting disc, we attempt to frustrate condensation during boiling liquid impact. We will discuss the effectiveness of counteracting the vapour condensation by heating in reducing the impact pressure on the disc.