Fabrication and characteristics of composite phase change material based on Ba(OH)2·8H2O for thermal energy storage

Abstract

Latent thermal energy storage using phase change material (PCM) is an effective way to store and transport energy. In this work, expanded graphite was modified using octylphenol polyoxyethylene ether to generate modified expanded graphite (MEG), and then a novel shape-stabilized Ba(OH)2·8H2O/MEG composite PCM was synthesized by incorporating Ba(OH)2·8H2O into MEG matrix. Mass fractions of Ba(OH)2·8H2O in composite PCM were calculated from 74% to 93%. The effects of MEG on properties of PCM were investigated using scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and thermal constant analyzer. The results indicated that MEG had the desired compatibility with Ba(OH)2·8H2O. The phase separation of Ba(OH)2·8H2O was effectively inhibited by the MEG matrix and the supercooling temperature decreased from 13°C for Ba(OH)2·8H2O to 2.4°C for composite PCM with a MEG matrix density of 200g/L. At the same matrix density, the thermal conductivity of composite PCM reached 3.58W/(mK), 1.84 times higher than that of Ba(OH)2·8H2O. The latent heat was approximately equal to the product of the latent heat of Ba(OH)2·8H2O and its mass fraction. Moreover, the enthalpy loss of the composite PCM was negligible after 400 cycles, showing good thermal reliability.