Accuracy of lumped element model for cyclic sensible thermal energy storage systems

Abstract

The sensible thermal energy storage system proposed in the present study is composed by a set of flat parallel plates and is meant to work as a thermal rectifier, continuously powered by a cyclical thermal stream in order to retrieve a conditioned output. The energy storage system is modeled by a lumped element model, but its accurateness needed to be ascertained. Computational fluid dynamic is used as a reference modeling to assess the lumped model deviations following a Design of Experiments planning, performed by the Box–Behnken method. Nine controlled and independent parameters are identified to operate the energy storage system, equally representative of the heat storage material, the plate geometry and the working fluid. The temporal evolution of the fluid temperature at the system discharge is used to observe the amplitude and phase deviations in respect to reference modeling. Amplitude deviations are found to be below 6% and phase deviations below 4% for 130 simulated cases assigned by the Box–Behnken method. Heat conduction along the plate axial direction is prevailing in respect to the transversal transfer, meaning that significant deviations from the lumped model to the reference one are only noticed when the storage system combines high values for the number of transfer units and the plate thermal conductivity. The present study shows that thermal energy storage systems like the one proposed in this paper can be simulated with lumped element models.