Investigation of low grade thermal energy storage systems with phase changing materials

Abstract

• Paraffin wax is a good storage medium due to fast charging and good latent heat absorption. • The two designs follow the same heating dynamics independently of the final temperatures reached. • An addition of a second inlet yields higher final temperatures and improves the HTF distribution. • This allows a better heat transfer rate, yet the temperature increase is minimal and negligible. • Higher or lower velocities at the inlet(s) can benefit the system depending on the design type. The use of phase changing materials (PCMs) for energy storage has been in the focus of scientific research for a while, primarily focusing on building cooling/heating applications due to favourable melting temperature ranges. In this paper we simulated the suitability of encapsulated Paraffin Wax on a small scale in a low temperature thermal energy storage system using COMSOL Multiphysics. Heat absorption and heating dynamics were analysed for different inlet designs and velocities, and the thermal gradient was evaluated across the tank geometry in a number of charging scenarios. Results show that paraffin wax proves to be a good storage medium based on its fast charging and good latent heat absorption. The study found that although an addition of a second inlet to the system yields higher final temperatures and improves the heat transfer rate, it does so minimally and therefore is not notably beneficial. Both designs follow the same heating dynamics independently on the final temperatures. Lastly, higher or lower velocities benefit the system based on the design.