  Thermal conduction was explored and discussed through a combined theoretical
and simulation approach in this work. The thermal conductivity k of
polycrystalline graphene was calculated by molecular dynamics simulations based
on a hexagonal patch model in close consistence with microstructural
characterization in experiments. The effects of grain size, alignment, and
temperature were identified with discussion on the microscopic phonon
scattering mechanisms. The effective thermal conductivity is found to increase
with the grain size and decrease with the mismatch angle and dislocation
density at the grain boundaries. The 1/T temperature dependence of k is
significantly weakened in the polycrystals. The effect of grain boundaries in
modifying thermal transport properties of graphene was characterized by their
effective width and thermal conductivity as an individual phase, which was
later included in a predictive effective medium model that showed degraded
reduction in thermal conductivity for grain larger than a few microns.
