Effects of various types of graphite on the thermal conductivity and energy storage properties of ternary eutectic fatty acid-based composite as phase change material

Energy is the greatest challenge facing the environment. Energy efficiency can be improved by energy storage by management of distribution networks, thereby reducing cost and improving energy usage efficiency. This research investigated the energy efficiency achieved by adding various types of graphite (e.g., flake and amorphous) to organic-based ternary eutectic mixtures like capric acid (CA)–myristic acid (MA)–palmitic acid (PA)-based composite phase change materials (PCMs) under the assistance of ultrasonication to improve thermal properties for thermal energy storage. The graphite was surface modified under a Fresnel lens by using concentration of solar rays, then exfoliation of flake graphite by solar irradiation (xG-F) and exfoliation of amorphous graphite by microwave irradiation (xG-A). For each type of graphite exfoliation, ternary eutectic mixtures with mass concentrations of 5 wt% were prepared. The structure, thermal energy storage properties, and thermal stability of the composite PCM were investigated. Thermal conductivity of the samples in the liquid phase was measured using the transient line source method (KD2Pro). The thermal conductivity was increased by loading xG while energy storage properties were slightly decreased. Furthermore, CA–MA–PA + 5 % xG-F has a slightly modified phase change temperature and enthalpy of melting ( T m = 17.5 °C; Δ H m = 143.7 J/g) and freezing ( T f = 6.7 °C; Δ H f = 125.5 J/g); this PCM showed higher thermal conductivity of 0.170 W/(m K), representing an increase of up to 114 % relative to the parent material. On the basis of the above results, xG-A was cheaper than xG-F, but they decrease the energy storage capacity according to DSC results obtained at 2 °C/min. CA–MA–PA/xG-F has more potential for use in low temperature energy storage applications.