Enhancement of solid-phase thermal conductivity and specific heat of solar salt through addition of MWCNT: new observations and implications for thermal energy storage

Solid-phase thermophysical properties of solar salt (a mixture of NaNO3 and KNO3) influence the performance of sensible heat and latent heat thermal energy storage systems. Solar salt's lower thermal conductivity imparts kinetic limitation during the discharge cycle and hence its thermal conductivity needs to be enhanced. This work is aimed at studying the influence of MWCNT incorporation on the improvement of solid-phase thermophysical properties of solar salt. Accordingly, experiments were carried out to study the influence of method of MWCNT-solar salt preparation, MWCNT concentration and temperature on solid-phase specific heat and thermal conductivity. Our results reveal that 0.5 wt% MWCNT-solar salt composite prepared by ultrasonication and milling for an appropriate time lead to 18.3% enhancement in the solid-phase thermal conductivity and 18% enhancement in the solid-phase specific heat. In addition, the total energy storage capacity over the temperature range of 50-270 degrees C (including solid-liquid phase change) is amplified by 11.5%. These results augur well for deployment of the MWCNT-solar salt composite in the thermal energy storage system as a storage medium.