Numerical Investigation of Hydrophobic and Superhydrophobic Surfaces for the Mitigation of Acid Dew Point Corrosion

The recovery of waste heat from post-combustion gases is often limited by sulfuric acid condensation, which promotes severe low-temperature corrosion. Hydrophobic and superhydrophobic coatings promote dropwise condensation rather than filmwise mode, potentially reducing the residence time of the condensed liquid on the surface. However, the dynamics of sulfuric acid dropwise condensation on such surfaces remain poorly understood. To address this gap, an individual-based model is developed to simulate the evolution of the condensing droplet population. Each droplet is tracked from nucleation to shear-driven sliding, accounting for growth by direct condensation and coalescence with other droplets. The heat and mass transfer model, used to evaluate the condensation rate of sulfuric acid for each droplet, includes latent heat transfer at the liquid–vapor interface and convection in the surrounding gas phase. Given its low mole fraction, all the sulfur trioxide is assumed to react with water to form sulfuric acid. Assuming that the wall temperature is below the acid dew point but above the water dew point, the composition of the condensed H2SO4-H2O solution is determined from vapor–liquid equilibrium (VLE). The numerical model is validated against experimental data from the literature. The results show that, compared with hydrophilic surfaces, superhydrophobic surfaces substantially reduce the wet fraction of solid substrate and the residence time of condensed droplets, suggesting a lower risk of low-temperature corrosion.