MgSO4-expanded graphite composites for mass and heat transfer enhancement of thermochemical energy storage

Abstract

Sorption based thermochemical energy storage using salt hydrates offers several potential advantages if engineered properly, compared with sensible and latent heat storage technologies, including low heat loss, small volume change and high energy density. Two of key technological challenges are low mechanical structure stability, which determines the life-span; and slow charging and discharging kinetics, which depends largely on mass and heat transfer. As the heat and mass transfer relates to structure and composition of thermochemical storage materials, the two key challenging aspects are coupled and the use of engineered composite thermochemical materials provides an avenue to address the challenges. In this paper, we report a novel thermochemical storage composite material, consisting of magnesium sulfate (MgSO4, the thermochemical storage material) and expanded graphite (EG, heat transfer enhancer and structural stabiliser), prepared by impregnation of MgSO4 into EG. The composite has been characterized by various methods, including scanning electron microscopy (SEM), differential scanning calorimeter (DSC), thermogravimetry (TG), transient plane heat source method and dynamic vapor sorption (DVS). The results showed that the MgSO4-EG composite containing 60% MgSO4 displayed superior heat and mass transfer properties. The hydration time of MgSO4 was shorten to about 1/4 of its pure and original form and the thermal conductivity was increased by more than 84.8% through the MgSO4 impregnation into EG.