A Coupled Molecular-Continuum Framework for Multiscale Simulations of Boiling

Abstract

Boiling is a perfect example of a multiscale process where molecular-level physics giving rise to bubble nucleation interact with larger-scale boundary layers determined by the outer system boundary conditions. We present a novel multiscale simulation method which merges Molecular Dynamics (MD) and Computational Fluid Dynamics (CFD) descriptions into a single modelling framework, where MD resolves the near-wall region where molecular interactions are important, and a CFD solver resolves the bulk flow. We model the progressive heating of a Lennard-Jones fluid via contact with a solid wall until a vapour bubble nucleates in the MD region of the domain and grows by entering in the CFD domain. Our results show that an incompressible CFD flow model based on the Volume Of Fluid (VOF) method with interphase mass transfer calculated via the Hertz-Knudsen-Schrage equation is sufficient to obtain seamless coupling of phase fraction, velocity and temperature fields, with the hybrid MD-CFD framework yielding bubble dynamics closely matching those of MD alone.