Low-grade heat collection from a latent heat thermal energy storage unit

Thermal energy storage is widely employed in waste heat recovery. Phase change materials (PCMs) are a type of promising thermal storage (TES) approach featuring high energy stored or released during melting and freezing. In this study, a latent heat storage system is designed to collect the waste heat from hot air while its efficiency is experimentally investigated. The system consists of five cuboid chambers to store PCMs and six air channels to deliver the exhausted gas. Paraffin wax is selected as the tested PCMs and differential scanning calorimetry (DSC) is applied to calibrate its melting range and latent heat. In the experiments, the effects of average air velocities and inlet air temperature on the performance of the latent heat storage unit are experimentally investigated. The experiments show that the designed TES unit can store maximally thermal energy for near 4510 kJ within 250 min, while the latent heat occupies 15 % at fan speed 25 RPM and the heater power with 2 kW. It is indicated that increasing of air mass flow rate and increasing of air inlet temperature can improve the heat transfer performance. It is found that the temperature profiles in the freezing process are smoother than those in the melting process.