Accelerated charging and discharging of a thermal energy storage system with multiwalled carbon nanotube – Adipic acid composites

Adipic acid functions as a thermal energy storage material possessing the latent heat storage density of ∼290 kJ/kg, with very little supercooling. The rate performance during the charging and discharging of thermal energy is impacted by its low thermal conductivity, which can be improved through the inclusion of high thermal conductivity and high-aspect ratio nanostructures. Multiwalled carbon nanotube - adipic acid nanocomposite was prepared using sulphuric acid-treated multiwalled carbon nanotubes (SA-MWCNT) at the concentrations of 0.1 and 0.2 wt%. The thermal conductivity measurements revealed the SA-MWCNT-adipic acid composite with 0.1 wt% SA-MWCNT to possess 16 % enhancement in thermal conductivity. The time duration required for melting of 0.1 wt% SA-MWCNT-adipic acid was reduced by 31 %, in comparison with that required for adipic acid. Also, 0.1 wt% SA-MWCNT-adipic acid composite required 32 % lower duration for release of the stored latent heat when cooled by a well-mixed liquid. The presence of SA-MWCNT in the composite contributed to improved kinetics for sensible heat energy storage also by amplifying the overall heat transfer coefficient by 35 % and 31 % during the solid phase heating and cooling cycles. This composite exhibited high stability after 250 thermal cycles relative to adipic acid. Hence, this SA-MWCNT-adipic acid composite is a suitable alternative to adipic acid in thermal energy storage systems for steam generation and water heating at elevated pressures.