Disodium Hydrogen Phosphate Dodecahydrate Shape-stable Composite Phase Change Material

In order to decrease building energy consumption and provide indoor thermal comfort,inorganic hydrated salt phase change materials?PCMs?with the advantages of high latent heat and energy density,wide source and low cost have attracted the attention of many researchers.However,inorganic hydrated salts PCMs suffer the issues of supercooling,phase separation and the leakage during solid-liquid phase change,which limit their application.In this paper,choosing Na₂HPO₄·12H₂O as main PCM,and respectively using hydrophilic fumed silica?Si O₂?with low thermal conductivity and Si O₂hydrophilic modified expanded graphite?MEG?with high thermal conductivity as porous carriers,the shape-stable composite phase change materials?CPCMs?,which are applied to building wall insulation material and radiant heating phase change floor,were fabricated by melting impregnation method.The effects of the mass fractions of Na₂Si O₃·9H₂O as the nucleating agent on supercooling and phase change performance of Na₂HPO₄·12H₂O were discussed.The obtained Na₂HPO₄·12H₂O PCM was compounded with fumed Si O₂ to prepare Na₂HPO₄·12H₂O/Si O₂form-stable CPCMs.In order to handle the problem that Na₂HPO₄·12H₂O lost part of crystal water?from 12 to 7?after composition,sucrose as an auxiliary additive was introduced,and the effects of the sucrose mass fractions on the phase change properties of CPCM were investigated.The shape-stable effect of CPCMs was analyzed.And the chemical composition,crystal structure and thermal reliability of the CPCM were characterized.The results indicated that adding 4%Na₂Si O₃·9H₂O could make the supercooling degree??35?T?of Na₂HPO₄·12H₂O decrease to 3.13°C,and addition of 3%sucrose could solve the dehydration problem of Na₂HPO₄·12H₂O in composites.The CPCM containing 30%Si O₂had excellent shape-stable effect and thermal properties with a suitable T_m?27.62°C?,high?35?H_m?119.5 J/g?and a low?35?T?2.72°C?.The FT-IR and XRD analysis results indicated that the Na₂HPO₄·12H₂O PCM had a physical interaction with Si O₂.After200 solidifying-melting cycles,shape-stable CPCM exhibited a good thermal reliability.In order to obtain the hydrophilic MEG,EG was modified by silica sol?Si O₂?,and the hydrophilic property of MEG was analyzed.The Na₂HPO₄·12H₂O PCM containing 4%Na₂Si O₃·9H₂O obtained above was compounded with MEG.And the sucrose was used to solve the dehydration problem of Na₂HPO₄·12H₂O in the composite system.Meanwhile,the phase change behaviors of Na₂HPO₄·12H₂O/MEG CPCMs in this process were studied.And shape-stable effect of the MEG mass fractions on CPCMs was discussed.FT-IR,XRD and200 solidifying-melting cycles were used to characterize shape-stable CPCMs.The results revealed that MEG contaning 15%Si O₂had the best hydrophilic property.Na₂HPO₄·12H₂O PCM containing 4%Na₂Si O₃·9H₂O and 3%sucrose was combined with 20%MEG to obtain the best shape-stable effect and thermal properties of CPCM.The obtained CPCM displayed a T_m of 33.52°C,?35?H_m of 158.5 J/g and?35?T of 2.29°C.Si O₂ formed a thin coating on the surface of EG by physical action.In shape-stable CPCM,MEG and Na₂HPO₄·12H₂O PCM were also physically combined.After 200 solidifying-melting cycles,Na₂HPO₄·12H₂O/MEG shape-stable CPCM exhibited stable thermal properties.