Experimental study on effective thermal conductivity of microcapsules based phase change composites

Abstract

As for thermal energy storage (TES) with phase change materials (PCM), thermal conductivity is a crucial property for heat storage/release rates and energy storage efficiency. In this study, a sort of new microcapsules based phase change composites (PCC) with carbon network to enhance the thermal conductivity and thermal stability was developed. The effective thermal conductivities of the as-prepared PCC were investigated by experiments and theoretical models. The influencing factors of PCC thermal conductivity were analyzed systematically. The morphology of PCC with carbon network structure was detected by energy dispersive spectroscopy using a scanning electron microscope. The experimental thermal conductivities were measured by the transient plane source method, while the theoretical ones were calculated by effective medium theory (ETM). Additionally, an effective theoretical model was proposed and modified to predict the thermal conductivity of such kind of composites with different mass fractions of expanded graphite (EG). As a result, obvious denser carbon network structure of PCC was further confirmed with 24wt.% EG, the corresponding thermal conductivity was increased by as much as 24 times of the pristine paraffin. The predictions of modified Agari-Uno model were in good agreement with the experiments. Negligible change in thermal conductivity of the PCC was proved after 500 heating and cooling cycles. Hence, the enhancement on thermal properties of PCC can be promising for further applications in TES system.