Numerical investigation and comparative analysis on heat transfer characteristics of organic phase change materials (OPCMs) and liquid metals (LMs) under flight acceleration conditions

Organic phase change materials (OPCMs) and liquid metals (LMs) are widely used in thermal energy storage (TES) and thermal management systems in aerospace applications, yet the effects of flight acceleration on their performance and clear selection criteria remain unclear. In this study, validated enthalpy-porosity numerical models were developed to compare the melting behavior of eicosane and gallium and to develop selection guidelines. The investigation revealed that gallium melts predominantly via heat conduction, while eicosane melts primarily through natural convection, attributable to gallium's thermal conductivity being 225 times greater than that of eicosane. Complete melting occurred in 14.68 s for gallium and 810.66 s for eicosane, with gallium exhibiting a volumetric latent heat of 489 MJ/m3 (2.5 times that of eicosane) and a heat storage rate of 3.33 kW compared to 0.024 kW for eicosane. Heat flux during eicosane melting remained around 10−1 W/cm2, whereas gallium reached up to 101 W/cm2. In applications with strict limitations on weight, insulation requirements, and susceptibility to corrosion, OPCMs are recommended, whereas in applications with low constraints, LMs are advised. Under flight acceleration, eicosane's melting time increased from 811 s under normal gravity to 1200 s in microgravity (a 48 % increase) and decreased by 56 % under hypergravity (ares = 19g). In contrast, gallium's melting time increased from 13.09 s in microgravity to 14.68 s under normal gravity (12 % increase) and to 20.69 s at 19g (58 % increase), as enhanced natural convection raised the temperature of the melted region. Dimensionless correlations for the melting fraction and Nusselt number were derived. These findings offer valuable insights for designing PCM-based TES and thermal management systems in aerospace applications, thereby enhancing reliability and efficiency under dynamic flight conditions.