Development of Phase-Change Materials with Improved Thermal Properties for Space-Related Applications

Abstract

For spacecraft thermal management systems, it is crucial to diminish the overall mass of onboard thermal storage system and minimize the temperature fluctuations when the environmental temperature changes drastically. Since there is no atmosphere in outer space, heat can only be rejected to space using radiation (e.g., radiators). The heat sink conditions, and the heating power subjected to be rejected vary continuously at the orbiting stage of the spacecraft. Without thermal storage capability, the radiator is required to be large enough to release the highest power at the hottest of the heat sink. Possessing a large latent heat of fusion, PCMs can store an enormous amount of thermal energy within a small volume, which makes them ideal for spacecraft thermal management systems. The heating power required to be rejected as well as the heat sink conditions vary steadily at the orbiting stage of spacecraft. Without thermal storage capability, the radiator is needed to be large enough to release the highest power at the hottest of the heat sink. By engaging and integrating phase-change materials (PCMs) into a passive two-phase heat exchanger, the radiator can be designed and sized for the average rather than the maximum power. This study aims to develop phase-change materials (PCMs) using nanostructured graphitic foams to enhance thermal conductivity of PCMs for improved thermal response in thermal storage applications. In the present study, the correlation of additive’s mass concentration and particle size on the thermal properties of PCM mixtures are investigated experimentally and numerically. Introduction of conductivity enhancing additives into the base PCMs will negatively affect the latent heat of fusion while improving thermal conductivity. Analytical and experimental results for latent heat of fusion are shown to be in good agreement, indicating that as mass concentration of graphitic foam (i.e., C-Foam) increases, the latent heat of PCM decreases consistently. The simulation results also reveal that a small fraction of porous C-Foam additives can significantly enhance thermal conductivity of the base PCM.