When dealing with numerical simulations of boiling phenomena, the spontaneous appearance of vapor bubbles is one of the most critical feature to be addressed. Capturing bubble formation during the dynamics, instead of patching vapor regions as initial conditions, is crucial for the correct evaluation of nucleation rates and nucleation site density, two of the most important parameters characterizing boiling. In this work the Diffuse Interface modeling for vapor–liquid systems is coupled with Fluctuating Hydrodynamics Theory to properly address this aspect and to analyze the detailed nucleation mechanism during boiling inception on a hot surface. The simulations revealed a new enhancing mechanism of bubble formation that is able to explain the low onset temperature measured in boiling experiments on ultra-smooth, wettable surfaces: the interaction and coalescence between sub-critical vapor embryos plays a fundamental role in lowering the onset temperature, increasing the lifetime of the embryos and their probability to trigger the phase change.
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