Thermal Diodes Based on Fractal Structures with Tunable Thermal Threshold

Abstract

The asymmetry of heat conduction in thermal diodes is attributed to the thermal regulation in thermal logic circuits, thermal control devices, etc. Currently, thermal rectification devices, however, are constrained by either specific on/off switching thresholds, or low sensitivity to manufacturing errors, as well as the restrictions for specific roughness and material characteristics. Here, a thermal diode based on fractal structures (inverted tapered branch channel, 5.7 mm branch length, and 4 branches) with liquid metal/insulator interface is proposed to avoid these existing constraints. The thermal rectification coefficient reaches 0.4704 (16.43 times larger than that of the basic structures) when the filling fraction only increases 1.33 times. The maximum temperature difference for the optimized thermal diodes is 18.31 °C when the heating temperature is 80 °C. By different arrangements of two thermal diodes mounted on chambers' surfaces, the interior temperatures range from 16.06 to 52.34 °C in the same ambient conditions (23.49 °C), indicating the excellent thermal regulation effect of the thermal diodes. These controlled temperature chambers can be applied in greenhouses or cold chain storage devices, more combinations with higher degree of thermal-threshold tunability offer possibilities in solving complicated thermal management problems and promote the energy utilization efficiency.

Advances of phononics in 2012–2022

“…These results provided a fundamental theoretical method for achieving macroscopic heat rectification. Moreover, based on fractal structures with liquid metal/insulator, Li et al [69] developed a thermal diode with the rectification up to 0.47. The optimal branch morphology and parameters of the diodes are shown in Fig.…”

“…[28] (b) Thermal diodes based on fractal structures of liquid metal/insulator with different branch morphologies, including tapered shape (β > 0), inverted tapered shape (β < 0), rectangular shape (β = 0), and topological branch. [69] (c) Mechanism, cyclic stability of the forward and reverse heat fluxes, and thermal rectification ratio of the flexible thermal diode. [70]…”

“…In contrast, when the caloric material is cooled with the caloric effect, the thermal diode allows the heat to flow only from the heat source to the caloric material and simultaneously prevents any heat flux from the heat sink to the caloric material. [80] [69] (b) Schematics of implementing thermal diodes in a caloric device. [80] (c) Schematic drawing of the thermal full adder.…”

“…However, the definition of thermal rectification ratio (r) varies in different papers. For example, [4,5,36,45,69,90,91]…”

“…Applications of phononic device. (a) Performance of thermal diodes on temperature chambers with different arrangements [69]. (b) Schematics of implementing thermal diodes in a caloric device [80].…”