On Phase Change Material Heat Exchangers: A Computational and Experimental Investigation
Dieppa, Christian Omar Rodriguez
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The emergence of ground- and airborne-based high energy laser (HEL) weapon systems has created a need for high-rate thermal energy storage (TES) devices that meet demanding size, weight, and power (SWaP) requirements for integration into the HEL thermal management system (TMS). Current and near-term HEL weapon systems produce thermal loads on the order of 30-300 kW when emitting, and approximately 5-10% of the peak load when in a non-emitting standby state. Emission to standby duty cycles of 10-50% are common, and therefore, sizing the TMS for real-time rejection of the peak thermal load is not practical. Accordingly, TES components can provide significant benefit to the TMS by storing thermal energy during emission and rejecting the stored energy during standby through a TMS sized for the time-averaged thermal load. To make TES devices practical for this application, gravimetric and volumetric storage densities greater than 150 kJ/kg and 150 MJ/m3, respectively, are required, while achieving storage rates equivalent to the peak HEL thermal load. In light of these requirements, researchers have looked to phase change materials (PCMs) as a potential solution. This investigation explores various architectures of phase change material heat exchangers (PCM-HX), and provides insights on a design methodology that can significantly reduce their development time. This work discusses major PCM-HX features and design principles regarding heat spreading techniques and material property characterization. Furthermore, the heat and mass transport phenomena within PCM-HX’s is described within a mathematical framework, and both steady state and transient calculations are presented. These formulations allow the analytical and computational design of a PCM-HX to explore the parametric impact of variables on performance and SWaP. Finally, a PCM-HX is instrumented and experimentally evaluated to examine the aforementioned design tool. Experimentally observed energy storage was within 5% of the computational predictions, which is well within typical margins for a rapid design tool.