Paraffin core -polymer shell micro -encapsulated phase change materials and expanded graphite particles as an enhanced energy storage medium in heat exchangers

The Micro-Encapsulated Phase Change Materials (MEPCMs) with the melting point temperature of 28 degrees C was used as an energy storage medium to control the thermal behaviour of a heat exchanger. The NEPCM particles were mixed with Expanded Graphite (EG) microparticles to improve the heat transfer rate in the heat exchanger. The MEPCM particles are made of paraffin cores with a particle average size of 45 mu m. The paraffin core of the particles can undergo a solid/liquid phase change and store a tremendous amount of thermal energy due to the latent heat of phase change. The heat exchanger is a copper pipe radiator with aluminium fins confined in either a bed of MEPCMs or a composite mixture of MEPCMs + Expanded Graphite (EG) microparticles. The thermophysical properties of MEPCMs and MEPCM + EG were measured. The outcomes show 132% enhancement in thermal conductivity and a 28% decrease in the sensible specific heat of the MEPCM + EG composite with the weight ratio of 70% MEPCM and 30% EG compared to pure MEPCM. The charging and discharging behaviour of heat exchanger for various flow rates and two cases of MEPCM and MEPCM + EG were studied experimentally. The results reveal that using EG notably enhances the heat transfer and capability of the heat exchanger during the charging and discharging process. Using MEPCM + EG reduces the temperature drop at the heat exchanger outlet about 15 degrees C compared to the case of pure MEPCM. (C) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.