Preparations And Properties Of Sodium Sulfate Decahydrate-disodium Hydrogen Phosphate Dodecahydrate Room Temperature Eutectic Salt Form-stable Composite Phase Change Materials

With the rising of people's living standards,the demand for indoor thermal comfort?22-28°C?is increasing.Integrating phase change material?PCM?with high heat storage capacity into building envelopes is an effective way to reduce building energy consumption by absorbing and releasing excess heat to improve indoor thermal comfort.In this paper,using the low-cost inorganic hydrated salts including sodium sulfate decahydrate?Na₂SO₄·10H₂O?and disodium hydrogen phosphate dodecahydrate?Na₂HPO₄·12H₂O?as the main raw materials,the hydrophilic fumed silica?SiO₂?and super absorbent polymer?SAP?as carriers,the preparations and thermal properties of Na₂SO₄·10H₂O-Na₂HPO₄·12H₂O room temperature eutectic salt PCM and its form-stable composite phase change materials?FSCPCMs?are studied.First,Na₂SO₄·10H₂O-Na₂HPO₄·12H₂O room temperature eutectic salt was obtained by adjusting the mass fractions?the same below?of Na₂SO₄·10H₂O and Na₂HPO₄·12H₂O and analyzing their thermal properties.The effects of nucleating agent and auxiliary nucleating agent on the supercooling degree of the eutectic salt were explored.The crystal structure and thermal stability of the obtained eutectic salt PCM were analyzed.The results showed that 20%Na₂SO₄·10H₂O and 80%Na₂HPO₄·12H₂O formed stable room temperature eutectic salt.The supercooling degree of the eutectic salt was reduced to 0.26°C by adding 2.5%sodium silicate?Na₂SiO₃·9H₂O?as main nucleating agent and 2.0%sucrose as auxiliary nucleating agent.The obtained eutectic salt PCM with phase change temperature of 25.86°C,melting enthalpy of210.0 J/g exhibited a good thermal stability.Secondly,the Na₂SO₄·10H₂O-Na₂HPO₄·12H₂O/SiO₂ FSCPCM was prepared by using SiO₂ as carrier with melting-dipping method.The thermal characteristics and supercooling degrees of the composites with different contents of SiO₂ were investigated.Leakage tests were conducted to explore the saturated adsorption capacity of SiO₂.The morphology,composition and crystalline phase were characterized.Besides,the thermal conductivity,heat resistance and thermal reliability were tested.The results showed that the FSCPCM was obtained successfully by adding 30%SiO₂,which revealed a low thermal conductivity and a good thermal reliability with phase change temperature of 25.16°C,supercooling degree of 0.24°C and melting enthalpy of 142.9 J/g.Finally,SAP was used as carrier to prepare Na₂SO₄·10H₂O-Na₂HPO₄·12H₂O/SAP FSCPCM by the absorption of SAP to hydrated salt.The thermal properties and supercooling degrees of the composite phase change materials with different mass fractions of SAP were studied.The saturated adsorption capacity of SAP was found by leakage tests.The crystallization property and chemical composition were characterized.The tests of thermal stability and reliability were conducted.The results demonstrated that the FSCPCM was obtained with 12%SAP.Its phase change temperature,supercooling degree and melting enthalpy were 25.03°C,0.22°C and 179.2 J/g,respectively.Additionally,it possessed low thermal conductivity and excellent thermal reliability.In summary,the two new developed FSCPCMs have dual functions of low thermal conductivity and high thermal storage,showing broad application prospects in the indoor thermal comfort improvement and building energy saving.