Enhanced thermal conductivity of form-stable composite phase-change materials with graphite hybridizing expanded perlite/paraffin

Phase change materials (PCMs) with paraffin waxes have been widely used in solar energy systems attributed to their favorable latent heat thermal energy storage (LHTES) properties. However, long-standing drawbacks of serious leakage in the melting state and low heat transfer property significantly limit their practical application in TES. Herein, we report a novel expanded perlite/paraffin/graphite powder (EP/P50/GP) composite formstable PCM (FSPCM) with enhanced thermal conductivity overcoming the drawbacks of paraffin. The effects of graphite particle (GP) size on the properties of composite FSPCM were investigated by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM). XRD and FTIR analysis suggested that there was favorable chemical compatibility among the composite FSPCMs. GP addition exhibited a positive influence on the thermal stability of EP/P50/GP composite FSPCMs. The smaller the GP size is, the better the dispersion of GP in the composite FSPCMs is. The thermal energy storage capacity per unit volume and cost of EP/P50/GP80 composite were also calculated as 1.95 x 10(7) kJ/m(3) and 23.49 $/kJ. The thermal conductivity of EP/P50/GP80 composite FSPCM was determined as 1.34 W/m.K, which showed the highest heat transfer rate in the all EP/P50/GP composite FSPCMs and was 4.15 times higher than that of P50 (0.26 W/m.K). After the thermal cycling tests, the prepared samples exhibited good thermal reliability, and the thermal conductivities were also further improved. Overall, GP showed apparent effects on the heat transfer rate and thermal behavior of the composite FSCPMs. The as-synthesized FSPCMs could have considerable promising in the solar energy systems.