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Transient thermal rectification in stacked polymer composites with a through-thickness BN microplatelet orientation gradient
Ryang-Im Kang and Dong-Wook Oh
Transient thermal rectification defined as the direction-dependent asymmetry in heat-transfer response before thermal equilibrium, offers a route to passive control of heat spreading without joining dissimilar materials or relying on phase transitions. This study numerically examines how a through-thickness gradient in boron nitride (BN) microplatelet orientation governs the transient response of a stacked anisotropic polymer composite. A two-dimensional,10-layer model with a total thickness of 3 mm was solved using COMSOL Multiphysics. Each layer was represented by a rotated effective thermal-conductivity tensor with principal values of 12.1 and 0.6 W·m−1·K−1, respectively. The convergent and divergent heat-flow configurations were generated by reversing the same layered structure relative to the heat source. The orientation profile was prescribed by a power-law function, and performance was quantified using peak and time-averaged thermal rectification ratios. For the baseline linear profile, the peak ratio reached 335% at 0.1 s, while the 30-s average was 21.8%. A single-objective genetic algorithm coupled to COMSOL optimized the bottom angle, top angle, and power-law exponent. The optimized peak ratio was 357%, and the 30-s average increased to 28%, corresponding to a 28.4% relative improvement. A nearly linear orientation-angle distribution maximized the peak thermal rectification ratio, whereas a power-law distribution with an exponent smaller than unity enhanced the time-averaged thermal rectification performance. These findings establish orientation-profile design as a tractable strategy for controlling transient heat spreading in bulk anisotropic composites.
Keywords: transient thermal rectification, anisotropic composite, graded orientation, heat conduction, orientation angle distribution, genetic algorithm
DOI: 10.32908/hthp.v55.2120