Experimental Study of the Enthalpy of the Diffuse Phase Transitions of Fullerene C60 Solutions in Industrial Paraffin Wax

Thermal energy storage (TES) units are an integral part of renewable and heat recovery power systems. Utilizing the phase change materials (PCMs) in TES units is considered to be a promising way to improve the efficiency of the power systems. The thermophysical properties of the PCM significantly affect the overall efficiency of the TES units. Nanotechnologies application is a long-term direction for improving the thermophysical properties of the PCMs for TES. Here we show that doping the industrial paraffin wax (PW) with fullerene C60 affects the value of enthalpy of the diffuse phase transition of composite PCM PW/C60 vs. pure PW. The conducted experiments indicated that the effect of C
60
on the caloric properties of PW during heating and cooling is different. The presence of 0.000120
$\mathrm{g}\cdot \mathrm{g}^{-1}$
and 0.000746
$\mathrm{g}\cdot \mathrm{g}^{-1}$
of C60 in the industrial PW led to an increase in the crystallization enthalpy of composite PCM up to (19…21) % and up to (31…35) %, respectively. In contrast, a decrease in the melting enthalpy was recorded in the same temperature ranges. The obtained effects can be explained by the occurrence of the diffused phase transitions in a wide temperature range and by the influence of C
60
fullerene admixtures on the internal structure of the PW in the liquid and solid phases. The obtained effects of C60 on the PW enthalpy of phase transitions indicate the expediency of further examination of the thermophysical properties of the various organic PCMs containing C
60
. The industrial implementation of the new generation of PCMs containing C
60
will contribute to improving the efficiency of the TES units.