Thermal performance enhancement of palmitic-stearic acid by adding graphene nanoplatelets and expanded graphite for thermal energy storage: A comparative study

The effects of adding GnPs (graphene nanoplatelets) (nanoscale) and EG (expanded graphite) (microscale) were investigated to improve the thermal performance of PA-SA (palmitic-stearic acid) eutectic mixture as a PCM (phase change material). Carbon materials were dispersed into PA-SA with loadings of 1wt%, 2wt%, 4wt%, and 8wt%. The thermal properties measurement results show that the phase change latent heats of composite PCMs decreased with increasing loadings. The thermal conductivities of the composite PCMs were measured by the transient plane heat source method. Both GnPs and EG can effectively improve the thermal conductivity of PA-SA, but EG is more effective due to its worm-like structure. For the highest loading (8wt%), the thermal conductivity of the composite PCMs is 2.7 times higher with GnPs and 15.8 times higher with EG than that of PA-SA at 25 °C. The thermal energy storage and release rates of the composite PCMs also increased due to the high thermal conductivity of carbon materials. The density of composite PCMs were found to increase with the addition of GnPs but to decrease with EG. All composite PCMs show good thermal reliability. This work shows that EG has the greater potential to enhance the thermal energy storage performance of PCMs. •Differences in effects of GnPs and EG on thermal performance of PCMs were studied.•The structural mechanism causing these differences was studied.•It's an almost linear relation between thermal conductivity and additives' content.•EG is more favourable than GnPs to enhance thermal conductivity.•GnPs and EG decrease melting temperature and increase freezing temperature of PCMs.