Preparation and thermal performances of Na2HPO4·12H2O/ SiO2 hydrophilic modified expanded graphite form-stable composite phase change material for radiant floor heating system

Based on Na2HPO4·12H2O as phase change material (PCM) and SiO2 hydrophilic modified expanded graphite (MEG) as supporting carrier and thermal conductivity enhancer, a novel Na2HPO4·12H2O/MEG form-stable composite PCM (CPCM) for radiant floor heating system was fabricated by physical mixing method. The SiO2 mass fraction in MEG and MEG content in CPCM were optimized. The adsorption performance of MEG on Na2HPO4·12H2O and morphology of MEG were systematically discussed. The shape stability, pore structure as well as thermal properties of the obtained CPCM were emphatically investigated. Experimental results showed that MEG containing 15% SiO2 possessed optimal hydrophilicity and adsorption capacity for Na2HPO4·12H2O. With MEG mass fraction of 20%, the CPCM exhibited suitable phase change temperature (33.52 °C), high phase change enthalpy (158.5 J/g), low supercooling degree (2.29 °C) as well as favorable thermal conductivity (1.077 W/m·K), along with the outstanding shape stability and thermal reliability. All these suggest that Na2HPO4·12H2O/MEG CPCM has great application potential in radiant floor heating system. In order to improve the hydrophilic performance of EG as a supporting material, acidic silica sol was used to cover a thin SiO2 nanoparticle hydrophilic coating on the surface of EG to obtain the MEG. Then, through a simple blending method, Na2HPO4·12H2O PCM was adsorbed by MEG to obtain Na2HPO4·12H2O/MEG CPCM through a simple blending method. [Display omitted] •MEG with SiO2 coating could improve the compatibility with Na2HPO4·12H2O PCM.•MEG could settle the leakage issue of PCM.•MEG could enhance the thermal conductivity of PCM.•The CPCM exhibited excellent thermal stability.