Preparation and thermal energy storage properties of d-Mannitol/expanded graphite composite phase change material

• A new type of D-Mannitol/expanded graphite composite PCM was prepared.
• The impact factors of thermal conductivity of composite PCM were analyzed.
• The thermal energy storage performance was improved by experimental test.

A d-Mannitol/expanded graphite(EG) composite phase change material(PCM) was prepared for solar thermal energy storage or waste heat recovery applications performed at 180–240 °C. EG was produced by microwave irradiation performed. It was found that the EG prepared exhibited the maximum sorption capacity of 85 wt% for d-Mannitol. Scanning electron microscopy (SEM) images showed that d-Mannitol was uniformly dispersed in the micro holes of EG. Differential scanning calorimeter (DSC) analysis indicated that the phase change temperature of the composite PCM was close to that of d-Mannitol, and its latent heat was equivalent to the calculated value based on the mass fraction of d-Mannitol in the composite. With the assistance of hot disk analyzer, the thermal conductivities of the composite PCM first rise and then drop with increasing of its densities, and similar linear relationships between the maximum thermal conductivity and mass fraction of expanded graphite or between corresponding compress density and mass fraction of expanded graphite were obtained. Thermal energy storage performance of the composite PCM was tested in latent thermal energy storage (LTES) system.The heat transfer in the composite PCM during the thermal energy storage process was enhanced through the thermal conductivity improvement, while the heat storage duration was affected by the mass fraction of EG and the apparent density of the composite PCM.