The Preparation And Characterization Of A Shape-stabilized Composite Phase Change Material Of Polyethylene Glycol/diatomite With Enhanced Thermal Performance

Nowadays,China's building energy consumption accounts for about 28% of total energy consumption.In this case,the idea of integrating PCMs into the traditional building materials has been a hot spot,taking advantage of solar energy in the form of latent heat to finish energy storage and release.Nevertheless,there are still two enduring defects for the practical use of PCMs in the traditional manner,which include the difficulty to handle when the phase transforms from solid to liquid,and the hysteresis of thermal response due to the low thermal conductivity.Thus,in our study,we used diatomite as supporting material to prepare the shape-stabilized composite PCM.Besides,our study also capitalized on the improvement of the thermal conductivity of diatomite-based composite PCM.Diatomite-based composite PCM can be used as a sort of feasible low weight material for energy storage in buildings,saving energy and reducing resource consumption.The method realizes high added value utilization of diatomite resource,which has obvious economic and social benefitsA shape-stabilized composite phase change materials was prepared by blending PEG and diatomite with a vacuum impregnation method.Diatomite was firstly subjected to the alkali leaching treatment to enlarge its specific surface area and pore size,making it more qualified to be a PEG supporting material.The maximum load of PEG was as high as 70% while PEG melts during the phase transformation,which was 46% higher than that of the raw diatomite.The maximum load of PEG is the highest value for the diatomite-based composite PCM in literature up to now.The fabricated composite can preserve its original shape without any PEG leakage even when subjected to a 200 melt-freeze cycle.Besides,the prepared composite PCM owns large latent heat,high thermal stability and long-term reliability.The apparent activation energy of PEG in the composite was 1031.85 kJ/mol,which was higher than that of PEG.Spherical-shaped crystalline Ag nanoparticles?AgNPs?with a diameter of 3¹0 nm and single-walled carbon nanotubes?SWCNs?were uniformly decorated onto the diatomite via a simple hydrothermal and solution blending process,respectively.After modification,both the specific surface area and porous structure were not affected.The shape-stabilized and high thermal-conductivie composite PCMs were further tailor-made by blending PEG and the two kinds of decorated diatomite.The thermal conductivity was 0.82 W/mK for the AgNPs-decorated?7.2 wt%?diatomite composite,which was enhanced by 240% compared to the pristine PEG.And the thermal conductivity was 0.82 W/mK for SWCN-decorated?2 wt%?diatomite composite,which was enhanced by 260% compared to the pristine PEG.The improved thermal conductivity caused the decrease of supercooling extent,melting and freezing times whilst maintaining the thermal storage density.LiNO₃/diatomite middle-temperature and Na2SO₄/diatomite high-temperature composite PCM were prepared via a mixing and sintering method.PCMs were well dispersed into diatomite pores.The composite PCMs were shape-stabilized even after a 200-cycle of melting and freezing.The working temperatures of LiNO₃/diatomite and Na2SO₄/diatomite were 240²55 oC and 877.61⁸87.61 oC.The obtained middle-,and high-temperature shape-stabilized composite PCMs own excellent thermal storage density,high thermal stability and good reliability.PEG/SiO₂ low-temperature and Na2SO₄/SiO₂ high-temperature shape-stabilized composite PCMs were respectively fabricated using the oil shale ash and TEOS as silicon source via the sol-gel method.The prepared composite PCMs were quite stable in terms of chemical and thermal properties even after a 200-cycle of melting and freezing.The obtained SiO₂-based composite PCMs own excellent thermal storage density,enhanced thermal conductivity,high thermal and shape stability.