Energy evolution of a droplet impacting a nonuniform chemically patterned fuel cell surface

A three-dimensional nonorthogonal lattice Boltzmann model is employed to simulate a single droplet impacting a nonuniform wettable surface at the bottom of a proton exchange membrane fuel cell. The effects of nonuniform surface wettability differences in the flow channel, the impact Weber number, and the central stripe width on the energy evolution during the spreading stage are investigated. Qualitative and quantitative comparisons between the numerical simulations and experimental results indicate that the main energy loss during the initial spreading stage is attributable to momentum redistribution, while viscous dissipation is caused by shear stress and vorticity in the rim. A larger wettability difference leads to a higher net unbalanced Young’s force, resulting in stronger shear and viscous dissipation near the wettability contrast line. For smaller Weber numbers, in the early impact stage, the main loss of kinetic energy is caused by the redistribution of momentum; in the later spreading stage, the increase in surface energy is the main sink of kinetic energy. The unbalanced Young’s force hinders the spreading of the droplet at larger stripe widths, leading to a larger vortex intensity within the rim.