An analysis based on the energy conservation is presented for the self-propelled droplet
during coalescence of two droplets of the same size over a superhydrophobic rough surface.
The self-propelled behavior occurs only for the coalescence of droplets with a certain range
of radius. An analytical relation is established among the coalescence-induced velocity,
surface energy, viscous dissipation, and droplet size if gravity is negligible. The coalescence-
induced velocity increases with increasing droplet size to a maximum and then decreases …