The Evaporation Microlayer in Nucleate Boiling: Theory and Numerical Simulations

Nucleate boiling occurs when the temperature of a solid surface in contact with a liquid is raised above the fluid saturation temperature. Vapour bubbles nucleate, grow until reaching millimetric sizes and eventually detach from the surface owing to buoyancy. The dissipation of the latent heat and the mixing induced by the bubbles provide exceptionally high heat transfer rates, making boiling an attractive thermal management technology, widely exploited in applications from electronics cooling to nuclear power. Recent experiments have evidenced that a growing vapour bubble may trap a micrometre-thick liquid film against the heated wall, known as the evaporation microlayer, where liquid evaporates vigorously greatly enhancing heat transfer. However, the mechanisms for its formation, its dynamics and heat exchange contribution remain unclear, and this has sparked significant interest in the boiling community, experimentalists and modellers alike. In this talk, I will present the results of our ongoing efforts on this topic, from theory to continuum- and molecular-scale simulations: (i) A theoretical model which predicts the microlayer thickness from an analogy with the Landau-Levich plate-withdrawal problem; (ii) The insight into the microlayer dynamics and heat transfer obtained with an interface capturing method implemented in OpenFOAM and validated versus experimental data from MIT; (iii) A hybrid continuum-molecular domain decomposition solver for multiscale simulations of boiling.