In the last years, it has been demonstrated that heat transport in some 2D materials like graphene could be described by the appearance of
hydrodynamic behavior. In bulk materials like silicon this contribution can be more subtle and can remain hidden inside the calculations or even
numerically removed. The Kinetic Collective Model (KCM) has been especially developed to provide the hydrodynamic contribution even in materials
where these effects are not dominant. From this formalism, the Guyer-Krumhansl equation is obtained as a generalization of the Fourier’s law including a
nonlocal term similar to that obtained in the Navier-Stokes equation. This framework offers an explanation to the deviations observed experimentally
respect to Fourier is low due to the appearance of hydrodynamic effects. The new equation provides new physical insight on heat transport as introduces
new phenomenological concepts like phonon viscosity or vorticity and can have an impact in applications.