  Understanding heat transfer characteristics of phase change and enhancing
thermal energy transport in nanoscale are of great interest in both theoretical
and practical applications. In the present study, we investigated the nanoscale
vaporization and condensation by using molecular dynamics simulation. A cuboid
system is modeled by placing hot and cold walls in the bottom and top ends and
filling with working fluid between the two walls. By setting two different high
temperatures for the hot wall, we showed the normal and explosive vaporizations
and their impacts on thermal transport. For the cold wall, the cuboid
nanostructures with fixed height, varied length, width ranging from 4 to 20
layers, and an interval of 4 layers are constructed to study the effects of
condensation induced by different nanostructures. For vaporization, the results
showed that higher temperature of the hot wall led to faster transport of the
working fluid as a cluster moving from the hot wall to the cold wall. However,
excessive temperature of the hot wall causes explosive boiling, which seems not
good for the transport of heat due to the less phase change of working fluid.
For condensation, the results indicate that nanostructure facilitates
condensation, which could be affected not only by the increased surface area
but also by the distances between surfaces of the nanostructures and the cold
end. There is an optimal nanosctructure scheme which maximizes the phase change
rate of the entire system.
