Abstract
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; ΔH m = 143.7 J/g) and freezing (T f = 6.7 °C; ΔH 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.
Highlights
Latent heat thermal energy storage (LHTES) has the advantages of high energy storage density and small temperature variation during the phase change process
The thermal energy storage properties of capric acid (CA)–myristic acid (MA)–PA and CA–MA–PA/xG were analyzed by differential scanning calorimetry (DSC, 200 F3, Maia, NETZSCH); the melting and heat storage behaviors of the pure phase change materials (PCMs) and composite PCMs were examined at 2 °C/min heating rate in the range of 0–40 °C under a constant flow of nitrogen
CA–MA–PA composites loaded with xG-F and xG-A were prepared with the aid of sonication to afford PCMs with high thermal conductivity
Summary
Latent heat thermal energy storage (LHTES) has the advantages of high energy storage density and small temperature variation during the phase change process. Phase change materials (PCMs) used in LHTES are generally categorized as inorganic and organic. Inorganic PCMs are salt hydrates, salts, metals, and alloy, have a high heat of fusion, good thermal conductivity, cheap and nonflammable, but their applications are limited due to corrosive to metals, undergo supercooling and phase decomposition. Paraffin materials have been widely used owing due to desirable thermal characteristics, such as minimal supercooling, varied phase change temperature, low vapor pressure in the melt, good thermal, chemical stability and self-nucleating behavior
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