Analysis of Thermal Diodes Enabled by Junctions of Phase Change Materials

Materials designed to undergo a phase transition at a prescribed temperature have been advanced as elements for controlling thermal flux. Such phase change materials can be used as components of reversible thermal diodes, or materials that favor heat flux in a preferred direction; however, a thorough mathematical analysis of such diodes is thus far absent from the literature. Herein, it is shown mathematically that the interface of a phase change material with a phase invariant one can function as a simple thermal diode. Design equations are derived for such phase change diodes, solving for the limits where the transition temperature falls within or outside of the temperature gradient across the device. Criteria are derived analytically for the choice of thermal conductivity of the invariant phase to maximize the rectification ratio. Finally, the model is applied to several experimental systems in the literature, providing bounds on observed performance. This model should aid in the development of materials capable of controlling heat flux.