Discharge performance of a thermal energy storage unit with paraffin-expanded graphite composite phase change materials

Thermal properties of paraffin wax (PA) and paraffin/expanded graphite (97% PA/3%EG and 95% PA/5%EG) composite materials were investigated. Heat release performance of thermal energy storage (TES) units with different diameters containing the phase change materials were studied at a drying media temperature of 25℃ and a media velocity of 0.8 m·s^-1. The results showed that the thermal conductivity of the composites was increased by 178.10% and 214.30% respectively compared with that of PA, which could shorten the TES unit discharge time. The diameter of the TES unit had a significant effect on the heat release performance. An increase in the diameter of the PA based TES unit leads to a linear increase in the heat release time, whereas an increased EG content reduces the heat release time of the unit for a given TES unit diameter. The effect of EG on the heat release performance of the TES unit increases first and then decreases with increasing diameter, leading to an optimal TES unit diameter of 35 mm under the conditions of this study.