  We analyze the coupling between conduction and radiative heat transfer in
near-field regime between two coaxial cylinders separated by a vacuum gap. By
solving the heat transport equation in the steady-state regime between metals
or polar materials we highlight a flux saturation mechanism for the radiative
transfer even without non-local effect. In the case of polar materials this
saturation occurs in the separation distances range of 1 to 10 nm which can be
experimentally explored.
