On the coupling between direct numerical simulation of nucleate boiling and a micro-region model at the contact line.

During the past years, numerical simulations of Nucleate Boiling have attracted increasing attention. If significant advances have already been performed on the conception of accurate numerical schemes accounting for jump conditions at a non-isothermal interface, further studies are required on the modeling of the heat flux in the vicinity of the contact line. Especially, at very low scale (<500 nm) the formation of a micro-region can be assumed, since the observed apparent contact angle can be higher than the microscopic contact angle and depend on the wall superheat. This variation of the apparent contact angle can be related to a temperature discontinuity between the saturation temperature and the local wall temperature at the contact line inducing a micro-region heat flux and an evaporation mass flow rate. Whereas this micro-region acts at very low scale, existing theoretical models suggest a strong influence of the micro-region heat flux on the global heat flux, and so on the overall bubble growth phenomenon. However, the numerical description of this micro-region in the framework of Direct Numerical Simulation (DNS) of nucleate boiling is a major issue due to the large range of spatial scales involved in the whole process. In the present paper, we propose a coupling methodology between an existing micro-region theoretical model and a larger scale DNS solver for Nucleate Boiling in axisymmetric configurations. Several benchmarks are proposed to show the consistency and the accuracy of the proposed method and to highlight the quantitative effect of the micro-region at the bubble scale. • A coupling between a DNS solver for nucleate boiling and micro-region model is proposed. • A specific boundary condition on the heat flux is proposed in the cells that contain the contact line. • A smoothing technique is proposed to spread the micro-region mass flow rate along the interface. • A novel benchmark based on experimental data is proposed to show the strong effect of the micro-region. • Nucleate boiling simulations in the micro-layer regime with micro-region at the contact line are presented. [ABSTRACT FROM AUTHOR]