Spatio-Temporal Analysis of Phase Change Material Based Heat Accumulator Under Space and Planetary Environment

Phase Change Materials (PCMs) are increasingly recognized for their potential in effective thermal management of space systems. PCM based heat accumulators maintain the temperature stability of electronic payloads in Spacecraft, Orbiters, and Landers, ensuring their reliability during operations. The primary challenge lies in understanding the complex convection dynamics that occurs during the solid-liquid phase transition. Key factors influencing the phase change dynamics in a space or planetary environment include the absence of atmospheric pressure, variations in incident heat flux, and low or varying gravitational acceleration. Under such conditions, the imbalance between convective and diffusive heat fluxes during the solid-liquid phase change leads to complex morphologies at the phase interface, which interfere with the effectiveness of heat transfer through the accumulator. In this study, we investigate the influence of variable gravity and its relative orientation with the global temperature gradient, defined by angle α, on the performance of the PCM-based heat accumulator. We study the spatio-temporal changes in flow dynamics across the orientation angle range from 0° to 180°, where, α = 180° corresponds to the alignment of the incoming heat flux with the gravity field, and α = 0° depicts the configuration where they are oriented in opposite direction. We conduct statistical analysis of coherent structures and global heat transport characteristics to examine the influence of variable gravitational conditions and orientation angles on the flow dynamics, heat transport, and thus the overall melting process of PCM. In addition, the variation in the energy storage capacity of PCM is provided under different operational conditions, which contributes to our understanding of the requirements for PCM in the design of thermal management systems for spacecraft.  The results are vital in assessing and designing a PCM-based heat accumulator for long-term passive thermal control in space and planetary environments.