Numerical study of dynamic melting enhancement in a latent heat thermal energy storage system

In the present work, a 2D Cartesian numerical model is implemented to simulate the transient behaviour of a latent heat thermal energy storage system under the effect of the dynamic melting enhancement technique. This enhancement technique consists of recirculating the liquid phase change material (PCM) during the melting process with an external pump and therefore increasing the overall heat transfer coefficient. Several simulations were carried out to study the influence of the PCM flow direction, the PCM velocity, and the heat gains in the PCM recirculation loop, showing in all cases the benefits of implementing this enhancement technique. Results from the simulations show that when the PCM flows from top to bottom, higher enhancements are obtained when compared to the PCM flowing from bottom to top. Moreover, it is observed that the higher the PCM velocity, the better the enhancement in terms of process duration and heat transfer rates. Additionally, the PCM velocity also has an influence over the evolution of the PCM melting front and thus over the evolution of the PCM temperature profiles. It is shown that the intensity of the enhancements, as well as the evolution of the melting front and temperature profiles, are more influenced by the PCM velocity than by the ratio between the heat transfer fluid (HTF) and PCM velocities. Finally, heat gains should be avoided in the PCM recirculation loop since they decrease the heat transfer rate between the PCM and the HTF.