  Transient heat dissipation in close-packed quasi-2D nanoline and 3D
nanocuboid hotspot systems is studied based on phonon Boltzmann transport
equation. It is found that, counter-intuitively, the heat dissipation
efficiency is not a monotonic function of the distance between adjacent
nanoscale heat sources: the heat dissipation efficiency reaches the highest
value when this distance is comparable to the phonon mean free path. This is
due to the competition of two thermal transport processes: quasiballistic
transport when phonons escape from the nanoscale heat source and the scattering
among phonons originating from adjacent nanoscale heat source.
