Fluctuating diffuse-interface simulations of vapor nucleation: Effects of wall superheat, wettability, chemical heterogeneity, and nanoscale topography

Surface modification affects both vapor formation and the heat transferred from a heated wall. These effects must be considered together when assessing surfaces for boiling applications. This study compares the effects of wall superheat, uniform wettability, chemical patterning and a nanoscale cavity under fixed wall-temperature conditions. A diffuse-interface model with thermal fluctuations is implemented in OpenFOAM to solve the conservation equations for mass, momentum and energy in a mesoscopic model fluid. The simulations follow vapor formation and growth from the initially liquid state, without a prescribed vapor seed, and measure the energy transferred from the wall during this process. Increasing the wall temperature from 620 to 638 K increases heat input and promotes sustained vapor growth. At 638 K, initially localized vapor regions grow and merge across the heated surface; at 620 K, persistent growth remains limited over the same interval. Increasing surface wettability by reducing the liquid-side equilibrium contact angle from 150° to 80° slightly delays the detected onset. Chemical patterns give similar onset times and cumulative heat input to a uniform wall with the same mean wettability. Over 0–200 ps, the cavity transfers 21.2% more cumulative energy than the flat wall over the same projected area. At 100 ps, its projected-area heat-transfer rate is 30.7% higher. Its actual heated area is 37.5% larger, so the energy transferred per unit heated area is lower. Among the cases studied, wall superheat has the strongest influence on sustained vapor formation. The heat-transfer comparisons show why vapor growth, heating duration and heated area must be considered together when interpreting nanoscale boiling inception.