Study on thermophysical properties of pentadecane and its composites with thermally expanded graphite as shape-stabilized phase change materials

We investigated the impact of thermally expanded graphite (ExG) on thermal conductivity and charging/discharging time for pristine pentadecane (PD), a potential phase change material for low-temperature thermal energy storage applications. The expanded graphite is prepared using a high-temperature (~ 950 ℃) thermal shock on chemically treated natural graphite flakes and is vacuum impregnated in pentadecane. Four different 5, 10, 15, and 20 mass% expanded graphite and pentadecane (PD-ExG) composite samples are considered for intensive studies of their thermophysical properties using differential scanning calorimeter (DSC), temperature history (T-history), and transient plane source measurements. DSC measurements showed the reduction in latent heat of fusion of pentadecane with increased mass% of ExG, but the melting temperature remained nearly unaffected. Further, thermal conductivity of pentadecane-expanded graphite composites enhanced from ~ 0.18 W m−1 K−1 (for pristine pentadecane) to 1.1 W m−1 K−1, 2.6 W m−1 K−1, 4.7 W m−1 K−1, and 7.1 W m−1 K−1 for 5, 10, 15, and 20 mass% ExG composite samples, respectively. The discharge time for these PD-ExG composites reduced about 42.7 to 67.81% as compared to pristine PD sample. PD-ExG composite with 10% or more ExG also showed the shape stability of PD-ExG composites and thus reduced leakage of PD in liquid state. Thus, PD-ExG form stable phase change material composite with enhanced thermal conductivity and enhanced charge/discharge rate, making it a suitable PCM for low-temperature thermal energy storage system such as space cooling.