Spherical and cylindrical conductive thermal diodes based on VO2

Abstract

We theoretically and comparatively study the performance of spherical and cylindrical conductive thermal diodes operating with a phase-change material, whose thermal conductivity significantly changes in a narrow interval of temperatures. Simple analytical expressions are derived for the temperature profiles, heat fluxes and optimal rectification factors of both diodes. It is shown that the diode geometry has a strong impact on the temperatures and heat fluxes, but not so much on the diode rectification factor. Optimal rectification factors of 20.8% and 20.7% are obtained for the spherical and cylindrical diodes operating with a temperature difference of 376 − 300 = 76 K and 376.5 − 300 = 76.5 K between the terminals of VO2 and a phase invariant material, respectively. These similar rectification factors could be enhanced with a material thermal conductivity exhibiting a faster phase transition and/or higher contrast than that of VO2. The obtained results can thus be useful to guide the development of phase change materials able to optimize the rectification of conductive thermal diodes with different geometries.