Packed bed thermal energy storage system using form-stable high-density polyethylene

Energy storage is a pressing need throughout a range of applications, and storage of thermal energy is an increasingly important element in energy management. This study describes the implementation and performance characterization of a new latent heat thermal energy storage system applicable to medium temperature processes requiring heat below 125 degrees C. The system utilizes a packed bed of form-stable polymer latent heat storage media. The media consists of a high-density polyethylene composite reinforced with glass fiber and a thin surface coating of epoxy resin. Stabilization with traditional composite synthesis approaches provides potential for low cost and high performance. The media is stable over repeated melting/solidification cycles and shows excellent thermal capacity, with more than 160 kJ/kg attributable to latent heat. We characterize the performance of direct contact heat exchange between the storage media and heat transfer fluids. The study includes effects of the mass flux of the heat transfer fluid, fluid inlet temperature during charging and discharging, and initial temperature of the porous bed. The system can be charged and discharged at relatively high rates, e.g. > 100 W/kg, and provides excellent energy density with high exergetic efficiency averaging approximately 79% (i.e. low temperature differences between charge and discharge). The approach presented offers opportunities to enhance the use of thermal storage in medium temperature applications (e.g. a charge/discharge operational range between 120 degrees C-140 degrees C).