Investigation on the effect of convective outflow boundary condition on the bubbles growth, rising and breakup dynamics of nucleate boiling

In this work, a phase-change lattice Boltzmann model was employed to simulate the effects of two computational domains with confined space and free outlet boundary considering the conjugate heat transfer on entire nucleate boiling. This model was validated by Laplace's law and droplet wetting process, especially in the improved convective outlet boundary for multiphase flow in detail. The film boiling was employed to verify the phase change model quantitatively, and the results exhibited a good agreement with a theoretical model so that the accuracy and robustness of the current model were ensured. The dynamic behaviors of the entire nucleate boiling including nucleation embryo, embryo growth, twin and triple vapors coalescence, departure, rise and subsequent rupture were investigated comprehensively. The temperature and velocity fields, as well as pressure propagations associated with nucleate boiling were investigated. The automatically sharp growth of nucleation vapor pushes away the vicinity of vapor outwardly, while the bottom fluid still flows into the root of the vapor contact line, which coincides with experimental observation. The flow dynamic behaviors of double and triple bubbles coalescence are almost the same, whereas more isolated bubbles merge is beneficial to the growth and departure dramatically. The sliding growth on the heating substrate was found clearly, which is mainly due to the nonuniform temperature gradient below the two side of the vapor bubble. The curvilinear rising trajectory and large deformation of rising vapor bubbles were observed, leading to a temperature wake in the rear of the rising bubble. The increasing volume of the rising bubbles occurred in the free outlet domain was found, which is mainly caused by the combined pressure influence between the inside and vicinity of the bubble. Moreover, the comparisons of nucleate boiling in both two computational domains were also studied.

Automated summary

In this study, a phase-change lattice Boltzmann model was used to simulate the nucleate boiling process in two computational domains with confined space and free outlet boundary. The model was validated and shown to be accurate and robust. The dynamic behaviors of nucleation, growth, coalescence, departure, and rupture were comprehensively investigated.