Improvement of a PCM-based thermal energy storage system

Nowadays phase change materials are encountering more and more interest in the scientific community mainly thanks to the fact that they can store a huge amount of heat per unit of volume respect to the traditional sensible storage materials. In fact, the use of PCMs is one of the best ways to store thermal energy. The peculiarity of those materials is that they store and release heat at a constant temperature during their phase change. The present work aims to study and characterize the thermal performance of a PCM-based latent heat exchanger (HE). The HE is composed by two coaxial cylinders in plexiglass (PVC) closed with PVC panels on both sides in which a smooth steel coil is present. The coil is immersed in the PCM which is a commercial paraffin with a melting point of 28 °C. To melt and solidify the PCM, hot and cold water respectively flows inside the coil. The purpose is to explore the melting and solidification process by monitoring the temperature in the HE with multiple thermocouples placed at different heights and different radial distances from the centre of the HE to the outer wall. Measurements are taken with thermocouple type T connected to instrumentations which collect all the measurements. In that way it is possible to create curves of temperature in which is possible to see when the melting and the solidification occur, the respective temperatures and other possible phenomena like for example the subcooling, which is a typical problem with most of PCMs. Knowing temperatures and the flow rate of water flowing into the coil throughout the process is possible to calculate the power of the HE and so the energies to characterize the whole system. After studied the system with the pure paraffin, tests with different percentage in mass of graphene oxide are carried out to see how the increase of the thermal conductivity enhance the overall performance of the heat exchanger and so compare also the PCM-based system with the same system filled with water which can be considered the reference for thermal storages nowadays.