Preparation and thermal properties investigation of pentaerythritol based phase change microcapsules for low and medium temperature thermal energy storage

Abstract

As one of classic organic compounds, pentaerythritol (PE) has been reported to have two phase-change processes with one solid-solid transition and other solid-liquid transition. To utilize these two phase-change enthalpies and avoid the liquid leakage over heat storage process, this work for the first time proposes to encapsulate PE with use of silicon dioxide (SiO2) as a shell substance through a so-called so-gel technology. The microstructure characterization and thermoproperties as well as the cycling performance of the PE- SiO2 composite are detailedly investigated. The results showed that PE could be successfully covered by SiO2 to form a spherical core-shell structure. Such an encapsulation has a mean size of 0.3 μm and an encapsulated rate of over 77.8 %. Due to the involvement of two phase-transition stages, the latent heat of the PE- SiO2 composite reached to 255 kJ/kg, which is higher than other organic microencapsulations. In addition, the thermal conductivity is largely enhanced by adjusting the ratio of SiO2. For a given SiO2 ratio of 77.8 %, the thermal conductivity of PE-SiO2 composite is 0.93 W/m·K, 36.8 % higher than that of pristine PE. Apart from these, the results also indicated that the composite achieves excellent thermal cycling performance. After one hundred repeated heating-cooling cycles, the latent heat of the PE- SiO2 composite decreases by less than 5 %, demonstrating that this composite material has a large potential for application in the field of thermal energy storage at low and medium temperatures.