Comparative Performance of Foam-Enhanced Eutectic Alloy and Organic Phase-Change Material Heat Sinks for Passive Thermal Management of Small Spacecraft

Possessing high latent heat of fusion and high thermal energy storage density, phase-change materials (PCMs) offer an energy-efficient and sustainable approach to passive thermal management. However, conventional organic PCMs such as paraffin wax exhibit inherently low thermal conductivity, resulting in high thermal resistance and slow thermal response. In contrast, eutectic alloy PCMs, particularly low-melting-point alloys (LMPAs), exhibit thermal conductivities nearly two orders of magnitude higher than those of paraffins, making them promising candidates for passive thermal management and thermal energy storage in spacecraft, where maintaining thermal stability and minimizing temperature fluctuations are critical due to substantial environmental variations during orbital operation. To address the thermal transport limitations of PCMs, this study experimentally investigates PCM-based heat sinks incorporating micro-structured metal foams and nano-structured graphitic carbon foams infiltrated with either a bismuth-based LMPA or paraffin PCM, both with a melting temperature of approximately 47 °C. The thermal performance of these heat sinks is evaluated under vacuum conditions representative of space environments by comparing their temperature responses and average thermal resistances. Foam-enhanced paraffin configurations incorporating copper and carbon foams are also examined for comparison with the LMPA-based systems. Baseline heat sinks containing pure paraffin and LMPA without conductivity enhancers are tested under both atmospheric and vacuum conditions, with the experimental baseline results validated against numerical simulations. The results demonstrate that foam-enhanced composite heat sinks improve average thermal resistance by nearly 22% relative to their corresponding baseline configurations. Moreover, foam-enhanced LMPA-based heat sinks achieve reductions of more than 50% in average thermal resistance compared with the base paraffin configuration, underscoring the potential of LMPA–foam composites for passive thermal management of battery modules and electronic components in spacecraft. Nevertheless, the mass of the base LMPA configuration is approximately 10 times that of the base paraffin configuration for an equivalent PCM volume, highlighting the trade-off between enhanced thermal performance and mass constraints in spacecraft applications.