Elsevier

Renewable Energy

Volume 147, Part 1, March 2020, Pages 1131-1138
Renewable Energy

Characterization and effects of thermal cycling on the properties of paraffin/expanded graphite composites

https://doi.org/10.1016/j.renene.2019.09.091Get rights and content
Under a Creative Commons license
open access

Highlights

  • EG addition can enhance PCM's thermal and electrical conductivity.

  • The properties of PCM composites changes after thermal cycles.

  • The PCM composite has good chemical stability after thermal cycles.

  • Thermal conductivity of the PCM composites was reduced after thermal cycles.

  • Electrical conductivity of the PCM composites was reduced after thermal cycles.

Abstract

Paraffin has been one of the most potential phase change materials (PCMs) in low-temperature latent heat storage. However, the low thermal conductivity of paraffin restricts its thermal performance and limits its large-scale applications. Adding a suitable proportion of expanded graphite (EG) into the paraffin can enhance the heat transfer rate, thus improve the thermal efficiency of the whole heat storage system. In this paper, five paraffin/EG composites with 2 wt%, 5 wt%, 10 wt%, 15 wt% and 20 wt% of EG were prepared to study their long-term characteristics. Effects of thermal cycling (up to 100 thermal cycles) on the thermophysical properties were studied, such as, phase transition temperature, latent heat, chemical compatibility, thermal stability and thermal conductivity. The paraffin/EG composite has the potential for converting intermittent electricity directly into heat, therefore, the effect of thermal cycling on electrical conductivity was also studied. The results showed that both phase transition temperature and latent heat decreased slightly after 100 thermal cycles, within 1% and 3% respectively. Thermal cycling changed the distribution and interaction between the paraffin and EG resulting in a lower temperature thermal decomposition process. Long-term thermal cycling also had a more negative effect on the increase rate in thermal and electrical conductivity achieved for higher EG content.

Keywords

Phase change materials (PCM)
Expanded graphite (EG)
Thermal conductivity
Electrical conductivity
Thermal cycling

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