Thermal diodes are materials that allow for the preferential directional transport of heat and are highly promising devices for energy conservation, energy harvesting, and information processing applications.  One form of a thermal diode consists of the junction between a phase change and phase invariant material, with rectification ratios that scale with the square root of the ratio of thermal conductivities of the two phases. In this work, we introduce and analyse the concept of a Dual Phase Change Thermal Diode (DPCTD) as the junction of two phase change materials with similar phase boundary temperatures but opposite temperature coefficients of thermal conductivity. Such systems possess a significantly enhanced optimal scaling of the rectification ratio as the square root of the product of the thermal conductivity ratios. Furthermore, we experimentally design and fabricate an ambient DPCTD enabled by the junction of an octadecane-impregnated polystyrene foam polymerized using a high internal phase emulsion template (PFH-O) and a poly(N-isopropylacrylamide) (PNIPAM) aqueous solution. The DPCTD shows a significantly enhanced thermal rectification ratio both experimentally (2.6) and theoretically (2.6) as compared with ideal thermal diodes composed only of the constituent materials. The agreement between experimental DPCTD and our analytical theory provides an engineering approach for the optimal design and operation of such elements. The DPCTD may find widespread application to thermal energy harvesting and conservation, and information processing, due to its high-performance under low, ambient temperature biases. <br/>

Dual phase change thermal diodes for enhanced rectification ratios: Theory and experiment

256th National Meeting (2018)

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