  The dynamics of two liquid droplets coalescing in their saturated vapor phase
are investigated by Lattice Boltzmann numerical simulations. Attention is paid
to the effect of the vapor phase on the formation and growth dynamics of the
liquid bridge in the viscous regime. We observe that the onset of the
coalescence occurs earlier and the expansion of the bridge initially proceeds
faster when the coalescence takes place in a saturated vapor compared to the
coalescence in a non-condensable gas. We argue that the initially faster
evolution of the coalescence in the saturated vapor is caused by the vapor
transport through condensation during the early stages of the coalescence.
