Thermal performance of a latent thermal energy storage for exploitation of renewables and waste heat: An experimental investigation based on an asymmetric plate heat exchanger

In this paper, the experimental characterization of a latent heat storage prototype working in the range of 70-90 °C and characterized by an innovative configuration is presented. The storage consists of a Phase Change Material (PCM), namely a commercial paraffin, embedded in an asymmetric plate heat exchanger. The testing campaign was aimed at defining the effect of operating conditions (flow rate of the heat transfer fluid, charge and discharge temperatures), in terms of energy stored, power supplied to the user and storage efficiency. The results showed that the energy density stored is between 116 and 198 kJ kg, whereas power output during discharge varies between 4 and 10 kW. Subsequently, an analysis on part load operation was carried out, which evidenced that properly managing the storage, limiting the discharging to 80% of its maximum storage capacity, allows saving around 50% of time, thus increasing the power density. A thermal network model was proposed to study the contributions of the heat exchanger and phase change material to the overall heat transfer, demonstrating that the phase change material is limiting the heat transfer only when it is in the solid state. Finally, the storage was compared to another prototype developed by the authors employing the same material and a different heat exchanger (a fin-and-tube heat exchanger) according to different structural, energy and dynamic performance indicators. The results highlighted that the present system is especially suitable for applications with a high power demand from the user.