Bubble Evolution and Properties in Homogeneous Nucleation Simulations

TL;DR

This study uses large-scale molecular dynamics simulations to analyze nano-bubbles during nucleation, revealing detailed properties such as density, temperature, shape, and interface thickness, with implications for understanding bubble growth in boiling and cavitation.

Contribution

It provides a detailed characterization of bubble evolution and properties during nucleation in a realistic simulation environment, highlighting differences from equilibrium assumptions.

Findings

Bubble gas densities are up to 50% lower than equilibrium vapor densities.

Bubble temperatures can be up to 25% below the surrounding liquid.

Near-critical bubbles are highly non-spherical but quickly become spherical.

Abstract

We analyze the properties of naturally formed nano-bubbles in Lennard-Jones molecular dynamics simulations of liquid-to-vapor nucleation in the boiling and the cavitation regimes. The large computational volumes provide a realistic environment at unchanging average temperature and liquid pressure, which allows us to accurately measure properties of bubbles from their inception as stable, critically sized bubbles, to their continued growth into the constant speed regime. Bubble gas densities are up to 50$%$ lower than the equilibrium vapor densities at the liquid temperature, yet quite close to the gas equilibrium density at the lower gas temperatures measured in the simulations: The latent heat of transformation results in bubble gas temperatures up to 25$%$ below those of the surrounding bulk liquid. In the case of rapid bubble growth - typical for the cavitation regime - compression of the liquid outside the bubble leads to local temperature increases of up to 5$%$, likely significant enough to alter the surface tension as well as the local viscosity. The liquid-vapor bubble interface is thinner than expected from planar coexistence simulations by up to $50%$. Bubbles near the critical size are extremely non-spherical, yet they quickly become spherical as they grow.