Effect of contact line evaporation during nucleate boiling studied by multiscale numerical simulation

The present paper studies the bubble growth in saturated nucleate boiling considering its multiscale physical behaviour for the isothermal heater case. The effect of evaporation occurring in a close vicinity of the triple contact line has been included through a subgrid microregion model describing the partial wetting case. The microregion model is analysed and compared to other existing approaches. Numerical simulations have been performed using the open-source code TRUST/TrioCFD coupled with the microregion model. The coupled solver calculates the phase change taking into account the evaporation from both the microregion and the macroregion. The interface position is determined with a combined front tracking and volume-of-fluid algorithm. The microregion heat flux is applied locally, without smearing it over the microregion. First, the default phase change model in TrioCFD was validated using benchmark tests based on the Stefan and Scriven problems. Next, the multiscale coupling approach was validated against existing experimental data on nucleate boiling. Our simulations show that microregion evaporation can contribute between 15% and 26% of total bubble growth, with this contribution becoming increasingly significant as superheating intensifies. Neglecting microregion effect leads to an underestimation of the heat fluxes, dry spot sizes and bubble growth rates, thus causing longer departure times; ultimately it can lead to a failure in capturing the bubble dynamics observed in experimental studies. • Multiscale simulations of single bubble growth in the nucleate boiling are performed. • 2D axisymmetric single bubble growth are considered for constant wall superheating. • Front-Tracking simulations (TRUST/TrioCFD) are coupled to a micro-region model. • The microregion heat flux is applied locally, without smearing. • An intermediate mesoregion is introduced to provide a smooth heat flux transition. • A case study is performed for 15 parameter sets. • Simulations in several cases are validated against several experimental datasets.