The size of condensate droplets departing from horizontal superhydrophobic copper surfaces and conventional aluminum alloy surfaces was studied experimentally and theoretically. During the whole condensation experiment

the dew formation and departure underneath the sample surfaces were imaged by CCD. It was found that the radius of the condensate droplets of the coalescence-induced jumping condensate departed from the superhydrophobic surface was below 300 μm. The coalesced droplets merged by micro-droplets with a radius ratio ranging from 1.0 to 1.5 were subject to self-removal from the superhydrophobic surface. This was because the driving force of the released surface energy after droplet coalescence became dominant compared to the resistance of the work of adhesion and viscous dissipation with the decrease of the radius ratio. In addition

the radii of the gravity-induced falling droplet from conventional aluminum alloy surfaces were ranged from 2.0 mm to 6.0 mm

and limited by the advancing and receding contact angles. Therefore

these results revealed that the superhydrophobic surface can significantly decrease the size of droplets departing from radiant ceiling panels and reduce condensation risks of radiant cooling ceiling systems.