Enhanced thermal conductivity of waste sawdust-based composite phase change materials with expanded graphite for thermal energy storage

Abstract

Background

With the current rapid economic growth, demands for energy are progressively increasing. Energy shortages have attracted significant attention due to the shrinking availability of non-renewable resources. Therefore, thermal energy storage is one of the solutions that lead to saving of fossil fuels and make systems more cost-effective by the storage of wasted thermal energy. In particular, the application of phase change materials (PCMs) is considered as an effective and efficient approach to thermal energy storage because of the high latent heat storage capacity at small temperature intervals. Nevertheless, leakage problems and low thermal conductivity limit the practical applications of PCMs. Therefore, form-stable phase change materials with high thermal conductivity are urgently needed.

Results

A novel form-stable composite phase change material was prepared by incorporating PEG into waste sawdust with 5% EG. In the composites, PEG served as a phase change material, while waste sawdust acted as a carrier matrix. EG was added to help increase the thermal conductivity of the composites. The melting temperature of CPCMs-4 with 5% EG was found to be 58.6 °C with a phase change enthalpy of 145.3 kJ/kg, while the solidifying temperature was 48.5 °C with a phase change enthalpy of 131.4 kJ/kg. The thermal conductivity of CPCMs-4 with 5% EG increased by 23.8% compared with that of CPCMs-4. Moreover, no obvious changes in melting, solidifying temperature, or latent heat after 200 heating–cooling cycles were detected. The supercooling extent of CPCMs-4 with 5% EG decreased by 19.2% compared with PEG. The volume change properties and wettability properties of CPCMs-4 with 5% EG are suitable for thermal energy in terms of practical application.

Conclusions

The prepared composites have excellent thermal and form-stable properties and they can be recognized as potential candidates for thermal energy storage as form-stable composite phase change materials. Using simple impregnation techniques with waste sawdust as a supporting material, this study demonstrates an innovative technology for practically and markedly enhancing the adsorption capacity of phase change materials.

Keywords

Phase change material / Waste sawdust / Second law of thermodynamics / Enhanced thermal conductivity / Wetting properties / Volume expansion percentage

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Funding

Fundamental Research Funds for Central Universities(2572015EB01)

National Natural Science Foundation of China(31770605)