Bridging the gap: Unraveling the role of nano-gas nuclei in the non-equilibrium water-vapor phase transition

Abstract

The mechanism governing the extensive range of cavitation pressures remains unclear due to the enigmatic nature of the non-equilibrium liquid–vapor phase transition at the cavitation inception, compounded by the complex interaction with nanoscopic gas nuclei. Moreover, conventional equations of state (EOS) also neglect the emerging intermediate states during this transition. In this study, molecular dynamics (MD) simulations and cavitation experiments are employed to investigate the liquid–vapor phase transition under adiabatic stretching conditions. We not only quantify the thermodynamic parameters at the meta-stability limit but also introduce a refined pressure model predicated on the void fraction. Our findings reveal a nuanced succession of five intermediate states from water to vapor, delineating a comprehensive pathway of the phase transition. The void fraction is a pivotal factor in reducing the cavitation pressure of bulk water from approximately $-140\mathrm{MPa}$ to nearly $-30\mathrm{MPa}$, which is embodied in the variability of gas-nuclei radius and number density. Utilizing the virial EOS, a relationship between bulk compressibility and density is established and further substantiated by the investigation of bulk modulus and sound velocity for validation. Our work furnishes a microscopic view of the non-equilibrium liquid–vapor transition, shedding light on the intricate processes underpinning the hydrodynamic cavitation in various application scenarios.