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Conductive Heat Transfer through Nanoconfined Gas: From Continuum to Free-Molecular Regime

In the past few decades, great efforts have been devoted to studying heat transfer on the nanoscale due to its importance in multiple technologies such as thermal control and sensing applications. Heat conduction through the nanoconfined gas medium differs from macroscopic predictions due to several reasons. The continuum assumption is broken down; the surface forces which extend deeper through the gas medium become prominent due to the large surface-to-volume ratio, and, finally, the gas molecules are accumulated nonuniformly on the solid surfaces. In this work, to better understand the combination of these phenomena on the heat conduction through the nanoconfined gas medium, we present a series of molecular dynamics simulations of argon gas confined between either metals or silicon walls. The gas density is set so that gas experiences a wide range of Knudsen numbers from continuum to the free molecular regime. It is observed that the intrinsic characteristics of the solid determine the gas density distribution near the walls and consequently in the bulk region, and these distributions control the heat conduction through the gas medium. While the nanochannel walls have their most significant impact on the density and temperature distributions of the rarefied gas, the pressure and the heat flux across the gas domain converge toward a plateau as the gas becomes denser. We propose new analytical formulas for calculating the gas pressure, induced heat flux, and effective thermal conductivity through the strongly nanoconfined gas, which incorporates the wall force field impacts on the gas transport characteristics for the Knudsen number in the range of 0.05 to 20.