Mathematical model of the inertia-controlled microlayer profile in nucleate boiling

Accurate simulation of the boiling heat transfer in a nuclear system requires extensive investigations of the microlayer dynamics during the nucleate boiling. In particular, the inertia-controlled microlayer profile, which plays a significant role in the microlayer evaporation and bubble dynamics, is the key parameter for the nucleate boiling simulation. In this work, the microlayer model in the inertia-controlled bubble growth stage was established through the disjoining pressure method and the lubrication theory. Two regions are distinguished: the contact line region, where the disjoining pressure is dominated; the microlayer region, where the effect of disjoining pressure fails, and the profile is determined by the balance of the surface tension and hydrodynamic forces. We found that in the contact line region, the profile is bent to approach the wall surface due to the disjoining pressure, while in the microlayer, the thickness increases almost linearly with respect to the microlayer length. The predicted profile was compared with experimental data and a very good agreement was obtained. Unlike the overestimated microlayer profiles from previous models, our results clearly demonstrate that the presence of the disjoining pressure is the key factor to supress microlayer thickness. Our model accurately captures the surface molecular force in the contact line region and provides the apparent contact angle for the microlayer. This offers a proper way to set up boundary conditions in the nucleate boiling simulations.