Study On Phase Change Energy Storage Performance And Mechanism Of Sodium Acetate Trihydrate

The inorganic hydrated salt sodium acetate trihydrate(SAT)phase change material(PCM)has merits of low cost,large latent heat and phase change temperature of 58?.It has broad application prospects in the fields of building heating,industrial waste heat recovery and solar heat storage.However,SAT suffers from severe latent heat attenuation after many melting and solidification cycles,which restricts its large-scale applications.Although a few of previous researches showed the attenuation could be effectively inhibited by using thickeners,the mechanisms of the attenuation process and thickeners'inhibition have not been deeply explored till now.In addition,the thermal energy currently used by SAT PCMs are mainly waste heat and a small amount of solar radiation.Among them,solar energy is one of the most promising clean energy sources,but the SAT's utilization of solar energy is not high.In response to these problems,this work firstly explored the latent heat attenuation process of SAT and the mechanism of thickeners'inhibition.Secondly,the photo-thermal conversion material was used to compound with the SAT,and the solar energy was used to drive the phase change of SAT,which exerted phase change energy storage performance of SAT PCM to improve solar energy utilization.The nucleating agent disodium hydrogen phosphate dodecahydrate(DSP)was used to reduce the supercooling of SAT.The composite PCM was melted and solidified for 200cycles,and the extent of latent heat attenuation,viscosity,phase composition and microstructure of the sample were analyzed.After 200 melting and solidification cycles,the latent heat of SAT decreased by 22.44%,because 24.1wt%anhydrous sodium acetate precipitated in the lower layer of the container to form a solid-liquid interface,which prevented the phase change of CH₃COONa under the interface during solidification.As a result,CH₃COONa without heat storage capacity accumulates at the bottom,causing the latent heat attenuation of SAT.Furthermore,the thickener carboxymethyl cellulose(CMC)was used to inhibit phase separation of SAT.The relatively light phase separation occurred in the SAT containing CMC,and the latent heat attenuation of the sample was small.It is because 3wt%CMC increased the viscosity of the sample and reduced the settling velocity of anhydrous sodium acetate.During the solidification process,most of the anhydrous sodium acetate can react with the liquid phase to form SAT,and the extent of latent heat attenuation was suppressed.The photo-thermal conversion material Ti₄O₇ particles were prepared using ilmenite as the titanium source,and the SAT photo-thermal conversion PCM with dual functions of photo-thermal conversion and thermal energy storage was prepared by combining Ti₄O₇particles with SAT using melt blending.DSP and CMC were used as nucleating agent and thickener to reduce supercooling and inhibit phase separation of SAT,respectively.The Ti₄O₇ particles with different mass ratios were added ino the SAT.The light absorption performance,crystalline structure,phase change performance,thermal performance,and photo-thermal conversion energy storage performance of SAT photo-thermal conversion PCM were characterized and analyzed.When the SAT contained 10wt%Ti₄O₇(S5D3C10T),it had excellent light absorption performance and contained most of the latent heat.The light absorption of S5D3C10T in the full spectral range(200-2500 nm)was93.33%,and the latent heat was 228.6 k J/kg.The photo-thermal conversion energy storage performance test result showed that its photo-thermal conversion energy storage efficiency reached 76.63%.