Form-stable quaternary nitrate salt-based composite phase change material with low melting temperature for low-medium-temperature thermal energy storage
A form-stable molten salt-based composite phase change material(PCM)with a low melting point suitable for low-medium-temperature thermal energy storage was prepared and investigated.A so-called cold compressing and hot sintering approach was used for the material preparation,in which a eutectic quaternary nitrate of NaNO3-NaNO2-KNO2-LiNO3 is utilized as the PCM,MgO as structure supporting material and graphite as thermal conductivity enhancer.A series of characterizations were performed to evaluate the composite microstructure,chemical compatibility,thermal properties,and cycling stability.The results showed that there was no chemical reaction among the quaternary nitrate,MgO,and graphite before and after sintering,indicating excellent chemical compatibility and stability in the composite.Among the different composite mass ratios,the 6∶4 quaternary nitrate-to-MgO mass ratio was optimal.In addition,the composite exhibited an excellent appearance when containing 8%graphite.A fairly low melting point of approximately 70℃and a relatively high decomposition temperature of 610℃were observed,offering the composite a large energy storage density exceeding 749 kJ/kg in the temperature range of 50-580℃.The thermal conductivity of the composite containing 8%graphite can be increased from 0.41 W/(m·K)to 0.77 W/(m·K).The composite exhibited excellent cycling stability after 150 heating-cooling cycles.This salt-based composite with a low melting point and a large temperature range is an excellent candidate for thermal energy storage,and this study offers a basis for its practical application in low-medium-temperature thermal energy storage fields.
quaternary nitratecomposite PCMlow melting pointlarge temperature rangethermal energy storage
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