Preparation And Properties Of Attapulgite Based Composite Phase Change Material With High Thermal Conductivity

Mineral-based composite phase change materials(PCMs)have a wide application prospect in solar energy storage systems as an environmentally friendly material with stable morphology,good thermal properties,simple preparation process and low cost.However,the low thermal conductivity of mineral materials limits the heat storage efficiency of composite PCMs.Therefore,the thermal conductivity enhancement process has an important significance.In this thesis,a series of composite PCMs with gradient phase change temperature have been prepared which the low-efficiency attapulgite act as the matrix material.The research on enhancing thermal conductivity was also carried out.Some important research results have been achieved.A series of composite phase change energy storage materials Atta/LA,Atta/PA and Atta/DA were prepared by vacuum impregnation method.Through thermal activation and acid activation modification process,the purity of attapulgite increases with the impurity phase dolomite disappears,and the specific surface area of attapulgite increases from 143.38 m~2/g to 222.23 m~2/g.In the composite PCMs of Atta/LA,Atta/PA and Atta/DA,the mass fraction of LA,PA and DA was 51.0%,50.8%and51.3%,respectively.The composite PCMs have good morphological stability,gradient phase transition temperature,high energy storage density and good thermal stability.The thermal enthalpy of composite PCMs was 94.6 J/g 107.5 J/g and 84.6 J/g,respectively,which are higher than those reported in the literature,and the thermal conductivity was enhanced to 0.22 W/(m·K),0.24 W/(m·K)and 0.22 W/(m·K),respectively.The Nano-Cu was dispersed in PCM by a one-step method using a high-power ultrasonic dispersion process,and the optimum mass fraction of Nano-Cu was 2 wt.%.Compared with LA?PA and DA,the thermal conductivity of LA@Cu,PA@Cu,and DA@Cu increased by 106.3%,105.6%,and 100.0%,respectively.The Atta/LA@Cu,Atta/PA@Cu and Atta/DA@Cu composite PCMs have good thermal stability and thermal cycle stability.Cu powder and Atta have synergistic enhancement effects on the thermal conductivity of PCMs.The thermal conductivity of Atta/LA@Cu,Atta/PA@Cu and Atta/DA@Cu was 0.46 W/(m·K),0.45 W/(m·K)and 0.43 W/(m·K).The Atta/GP matrix with high thermal conductivity was prepared by ultrasonic dispersion process,which graphite powder(GP)act as the thermal conductivity enhancer.The series composite PCMs of Atta/GP/LA,Atta/GP/PA and Atta/GP/DA have high energy storage density,excellent thermal stability and high thermal cycle stability.The degree of supercooling of composite PCMs was reduced by 1.4°C,0.6°C and 1.5°C,respectively.The thermal conductivity of composite PCMs reached 0.41W/(m·K),0.39 W/(m·K)and 0.37 W/(m·K),respectively,which increased by 156.3%,133.3%and 117.6%compared with PCMs of LA?PA and DA.The thermal storage and release time are also greatly shortened.The Nano-Fe particles were formed by the liquid phase reduction method on the surface and the holes of attapulgite,and the mass fraction of Nano-Fe was 2.34%.Atta@Fe/LA,Atta@Fe/PA and Atta@Fe/DA composite PCMs were prepared by vacuum impregnation method.The loading of phase change materials reached 58.2%,57.3%and 59.1%,respectively.The Att@Fe/LA,Atta@Fe/PA and Atta@Fe/DA composite PCMs with gradient phase change temperature are suitable for solar energy storage systems.Att@Fe/LA,Atta@Fe/PA and Atta@Fe/DA have good thermal stability and thermal cycle stability with thermal enthalpies of 87.0 J/g,110.1 J/g and99.6 J/g,respectively.Nano-Fe enhanced thermal conductivity of Atta which reach to0.50 W/(m·K).The the thermal conductivity of Atta@Fe/LA,Atta@Fe/PA and Atta@Fe/DA are 0.28 W/(m·K),0.34 W/(m·K),and 0.36 W/(m·K),respectively.