Simplified Analytical Formulation for Thermal Behavior Prediction of a PCM-Based Heat Storage System

The use of Latent Thermal Energy Storage (LTES) systems in Adiabatic Compressed Air Energy Storage (ACAES) systems is expected to significantly improve the performance of electricity-generating turbines. This improvement is particularly notable when medium- and high-temperature Phase Change Materials (PCM's) are employed as the storage medium. The relevant literature is abundant with analytical formulations that are intended to model the thermal behavior of large-scale PCM-based LTES systems. While these formulations offer valuable insights, they are mostly validated using experimental or theoretical studies conducted on reduced versions of the full-size storage systems. In an attempt to build on existing literature, this paper proposes an analytical model to simulate the thermal behavior of an industrial-scale PCM-based Shell-and-Tube Heat Exchanger (STHE). In this configuration, compressed air flowing in the shell exchanges heat with a medium- or high-temperature PCM stored in the tubes. The analytical model was validated using a series of Ansys® Fluent® Computational Fluid Dynamics (CFD) simulations conducted on a full-scale model using a variety of PCM's. It was demonstrated that the analytical model, which is based on the Kern method, can successfully predict the PCM phase change fraction evolution with a Root Mean Square Error (RMSE) of less than 0.05, and the compressed air outlet temperature with a Mean Absolute Percentage Error (MAPE) of less than 3%, for PCM Stefan numbers less than 2, at a speed 864 times faster than CFD simulations. Hence, the proposed model can serve as a quick remedy for resource-intensive CFD simulations and costly experiments, which further promotes the integration of PCM-based LTES systems into A-CAES systems.