Shape-stabilized phase change materials based on fatty acid eutectics/expanded graphite composites for thermal storage

Despite the well-known properties of organic phase change materials (PCMs), drawbacks including high phase transformation point, fluid leakage, and low thermal conductivity limit their practical applications. In this study, a kind of PCMs with low melting point (below 25 °C) was prepared using capric and lauric acid as substrates with additive oleic acid (C-L-O acid). C-L-O acid was then impregnated into worm-like expanded graphite (EG) to form the shape-stabilized PCMs (SPCMs) without any chemical reaction. EG was used to be not only a heat transfer intensifier, but also a shape-stabilized container for C-L-O acid. The melting enthalpy (ΔHm) of the SPCMs (mass ratio of EG to C-L-O acid was 1:35) was calculated to be 114.65 J/g, which was extremely close to the value of original C-L-O acid (115.91 J/g). The thermal conductivity of the SPCMs (1:5) was measured to be 3.15 W/m K, which was 22.5 times higher than that of original acid (0.14 W/m K). The SPCMs also showed good thermal reliability after thermal treatment cycles measurements. With consideration of latent heat and thermal conductivity, the SPCMs (1:15) were eventually selected as the optimal SPCMs with their ΔHm of 109.18 J/g and thermal conductivity of 1.95 W/m K. These composite SPCMs can be easily mass prepared and further used as potential materials for practical radiant cooling system.