  We study nondiffusive thermal transport by phonons at small distances within
the framework of the Boltzmann transport equation (BTE) and demonstrate that
the transport is significantly affected by the distribution of phonons emitted
by the source. We discuss analytical solutions of the steady-state BTE for a
source with a sinusoidal spatial profile, as well as for a three- dimensional
Gaussian hot spot, and provide numerical results for single crystal silicon at
room temperature. If a micro/nanoscale heat source produces a thermal phonon
distribution, it gets hotter than predicted by the heat diffusion equation;
however, if the source predominantly produces low-frequency acoustic phonons
with long mean free paths, it may get significantly cooler than predicted by
the heat equation, yielding an enhanced heat transport.
