Preparation and properties of stearic acid–palmitic acid-based shaped composite phase change materials

Abstract

Phase change materials (PCM) are pivotal in addressing the inherent intermittence and instability in solar heating applications by providing effective energy storage. A novel shaped PCM is fabricated by integrating modified graphite into a composite PCM substrate, using expanded graphite (EG) as a support, and modifying it with myristic acid to form modified exfoliated graphite (MEG), followed by melt blending and infiltration. The optimal mass ratio of the composite binary eutectic PCM—palmitic acid (PA) and stearic acid (SA) modified with 0.5 wt% of MEG (PA–SA/MEG_0.5)—to EG is determined to be 11:1, achieving an ideal composite density of 750 kg/m³. The PSMEEG₇₅₀ material, composed of PA, SA, MEG, and EG at a shaping density of 750 kg/m³ shows melting and solidification temperatures close to PA–SA, at 54.06 °C and 53.68 °C, respectively. However, its latent heats are slightly smaller (182.80 J/g and 177.70 J/g) compared to PA–SA. Notably, the thermal conductivity of PSMEEG₇₅₀ is 20.8 times greater than PA–SA, reaching 5.63 W/(m∙K), with a 17.2 % increase in specific heat capacity. After 1000 thermal cycles, the phase change latent heat of PSMEEG₇₅₀ only decreases by 4–4.5 %, indicating excellent leak prevention, heat storage capability, and thermal cycle stability. When integrated into solar heating systems and validated through Fluent software simulations, PSMEEG₇₅₀ requires less time to reach the heat storage plateau compared to PA–SA, with a relative increase in heat storage time of 26.39 %. Thus, PSMEEG₇₅₀ is a promising material for medium- and low-temperature solar phase change thermal energy storage systems.