Dynamics of wall bubbles in flash evaporation systems: Heterogeneous expansion and microlayer development

Abstract

This study employs the Lattice Boltzmann method to investigate the expansion dynamics of a wall-attached bubble in a flashing chamber. The computational framework is validated against thermodynamic consistency and the Young-Laplace law. Results reveal that bubble expansion follows the Rayleigh-Plesset equation. On hydrophilic surfaces, the contact line movement rate is positively correlated with the contact angle. In contrast, hydrophobic surfaces exhibit an extremely rapid contact line movement rate near a contact angle of ${120}^{°}$, due to coupled pressure-driven inertial and liquid jet entrance forces. A liquid microlayer forms on hydrophilic surfaces but is absent on hydrophobic ones, with its thickness stabilizing after four expansion cycles, following a power-law relationship with lateral spatial variables and an inverse-power-law relationship with the Reynolds number. The contact angle significantly impacts the power-law index. These findings elucidate how inertial, viscous, and capillary forces govern bubble dynamics, providing insights into flash evaporation mechanism in nuclear engineering.