Phase change materials offer thermal energy storage (TES) and are often integrated with high conductivity materials to increase power density. However, the design and optimization of such composites are historically based on intuition, as the computational techniques used to predict behavior in these systems are generally too expensive to perform parametric studies. Herein, a general design framework is developed and demonstrated that is optimized for TES in parallel lamellar structures, to identify the critical pitch required to treat the composite as a single effective medium and the optimum volume fraction of high conductivity material in the lamellar composite. The optimization criteria is tested experimentally using 3D printed AlSi12 alloy and octadecane. The composite system exhibits a critical pitch between a lamella of 1 mm and the optimum volume fraction for the high conductivity material is 0.6–0.8. The design principles demonstrated here show that the size and volumes of conductive materials are much larger than the current state of the art, and this framework provides a holistic approach to design for such future materials for TES applications.
Phase‐change materials (PCMs) and high‐conductivity elements can be combined to form highly compact and efficient composite heat sinks. However, the design challenge presented by thermal composites composed of PCMs and high‐conductivity elements remains unresolved. Herein, design guidelines are presented for radially varying cylindrical PCM composites. Numerical and analytical techniques are utilized to explore the utility and limits of optimal composite designs selecting for 1) temperature minimization, 2) specific effective heat capacity maximization, and 3) volumetric effective heat capacity maximization. Significant increases in each metric are observed when implementing radially variant designs in cylindrical geometries, especially for metrics of heat capacity. Furthermore, a hybrid approach to variant composite design is presented, allowing for the balancing of different design objectives. The utilization of a variable design under high heat flux (10 ± 1.4 W cm−2) and short melting periods (up to 50 s) is experimentally demonstrated, directly resulted in a 65% decrease in total system mass and a 200% increase in specific heat capacity while maintaining strong temperature dampening performance. In a second case study, a 23% decrease in mass is demonstrated while maintaining strong specific heat performance, emphasizing the broad utility of this approach.
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