Preparation And Thermal Properties Of Inorganic Hydrated Salt Composite Phase Change Materials

With the rapid development of the global economy,the shortage of fossil energy and environmental pollution have become increasingly prominent.Therefore,it is urgent to save energy,reduce emissions,and improve energy utilization.Phase change materials(PCMs)have been widely used in the fields of solar energy,building energy conservation,refrigeration logistics,power system,heat recovery,air conditioning,and household appliances due to their excellent latent heat storage,energy absorption,and temperature stability.Moreover,inorganic hydrated salt phase change materials belong to inorganic PCMs,which have non-toxicity,excellent thermal conductivity,and high phase change latent heat.In recent,it has become a hot spot in the energy storage field.However,its supercooling,phase separation and leakage problems hinder its promotion.Aiming at the above shortcomings,this study uses nanomaterials as nucleating agents to study the influence of nano-SiO₂and graphene oxide(GO)doping on the supercooling and phase change performance of sodium sulfate decahydrate(Na₂SO₄·10H₂O)PCMs.By preparing a phase change energy storage material with nano-SiO₂as the wall material and sodium sulfate decahydrate(Na₂SO₄·10H₂O)as the core material,the effects of microencapsulation on the thermal properties of the PCMs were studied.The main conclusions are as follows:First,the nano-SiO₂was synthesized by the sol-gel method,and the effects of different content of nano-SiO₂on the nucleation and thermal properties of Na₂SO₄·10H₂O were compared.The results showed that the small particle size of the as-prepared nano-SiO₂can act as a nucleus to promote the nucleation of Na₂SO₄·10H₂O.When the addition content of nano-SiO₂reached 2 wt%,the supercooling degree of Na₂SO₄·10H₂O decreased from 10.2?to 3.6?,the phase change temperature was 29.8?,and the phase change latent heat was 176.9 J/g.As the SiO₂content increased,the supercooling degree did not continue to change and remained at about 3.7°C.FT-IR and XRD results showed that there was a physical bond between nano-SiO₂and Na₂SO₄·10H₂O without chemical interaction.After 100cycles,the phase change latent heat was reduced to 69.7 J/g,and the supercooling was2.9?.The incorporation of nano-SiO₂can effectively reduce the supercooling of Na₂SO₄·10H₂O,but the effects of improving its cycle performance were not obvious.Subsequently,the GO-SiO₂materials were fabricated by the composite of graphite oxide(GO)and nano-SiO₂,and the influences of GO-SiO₂doping on the crystallization and phase change properties of Na₂SO₄·10H₂O were studied.The results showed that when the content of GO was 0.25 wt%and the content of nano-SiO₂was 2 wt%,the supercooling of the composite PCMs was 1.2?,the phase change temperature was 32.5?,the enthalpy of fusion was about 182.7 J/g,and the enthalpy of crystallization was about 163.4 J/g,and the thermal conductivity was0.6934 W/(m·K)which was 37%higher than the unencapsulated Na₂SO₄·10H₂O.After 100 cycles,the phase change enthalpy,crystallization performance,and phase change temperature of the composite PCMs had no change.After the cycle,the melting enthalpy was 159.2 J/g,and the solidification enthalpy was 127.9 J/g,which were only reduced by 13%and 22%compared to before the cycle,respectively.Finally,the microcapsule PCMs with SiO₂as the wall material and Na₂SO₄·10H₂O as the core material were successfully prepared by the sol-gel method.The effects of different reaction times on the thermal properties of the microcapsule PCMs were investigated.FT-IR and XRD showed that there was no chemical reaction between the core materials of the microcapsules,indicating that the two materials had good compatibility.When the reaction time reached 24 h,a microcapsule phase change material with excellent impermeability was prepared.Meanwhile,SEM showed that the microcapsule had a uniform particle size and an obvious shell structure.DSC indicated that the melting temperature of the microcapsule PCMs was31.02?,and the phase change latent heat was 168.6 J/g.After 100 cycles,the as-prepared microcapsule PCMs still maintained good phase change performance.After the cycle,the phase change temperature was 32.83?,the phase change latent heat was 148.2 J/g,and the phase change temperature and phase change enthalpy had a little change.Through the encapsulation of microcapsules,the cycle stability and thermal performance of Na₂SO₄·10H₂O have been significantly improved.