Understanding Trade-Offs of Phase Change Materials for Transient Thermal Mitigation

There are many applications throughout the military and commercial industries whose thermal profiles are dominated by intermittent and/or periodic pulsed thermal loads. Typical thermal solutions are steady state heat sinks that provide enough continuous cooling capacity to address the peak thermal load as if it were a steady-state condition. Such a conservative approach guarantees satisfying the thermal challenge, but it can result in significant cooling overdesign. This work investigates improving system size and weight without sacrificing platform performance by developing a package focused on transient thermal mitigation using timescale matched (TSM) phase change materials (PCMs). The TSM PCMs comprise both metallic and organic PCMs that enable each other. This work demonstrates that for short pulses, metallic PCMs have a fast thermal response due to their high thermal conductivity (high-k) but their weight, cost, and integration complexity limits their viability in applications. Alternatively, organic PCMs are inexpensive, lightweight, and can have very high latent heat of fusion but have very low thermal conductivity (low-k) compared to metals and thus cannot absorb heat quickly. The concept of time-scale matching will be presented as well as a numerical study outlining design trade-offs, packaging considerations, and the five time scale matching regimes. The paper will conclude with a Monto Carlo analysis showing a Pareto front of the optimal solutions when integrating copper, a metallic PCM and an organic PCM simultaneously and the solution families that are created.