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

Abstract

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.