Mesoscopic description of boundary effects in nanoscale heat transport

We review some of the most important phenomena due to the -wall collisions in nonlocal heat transport in nanosystems, show how they may be described through certain boundary conditions in phonon hydrodynamics. Heat in nanowires of different cross sections and in layers is analyzed, and the dependence of the thermal on the geometry, as well as on the roughness pointed out. We also analyze the effects of the roughness the surface of the pores on the thermal conductivity of silicon. Thermoelectric effects are considered as well.