Several authors have established single-tank packed-bed storage as a promising alternative that can be coupled with renewable thermal energy sources. The use of such systems can ensure a cost reduction of approximately 33%, compared to two-tank systems, which represents the dominating solution for high-temperature storage. Herein, an overview of the modeling approaches for assessing the yield and efficiency of packed-bed energy storage systems is presented. Additionally, the validation approaches used as well as the conventional materials and structures employed in such systems are described. One of the critical issues that affect the simulation models' performance in packed-bed energy storage systems is the treatment of the radiation exchange among particles. The impacts of the radiation phenomena on the overall performance and internal temperature distribution of the tank, which facilitate the identification of the operating conditions within the influence of radiation and are significant for analytical purposes are discussed herein. Through parametric analysis, it is demonstrated that the radiation heat transfer coefficient could be as high as 32% of the magnitude of the convection coefficient; thus, it should not be underestimated when analyzing operation temperatures above 750 degrees C.

The present study describes a CFD based methodology for the analysis of temperature stratification in an air thermocline tank using a three-dimensional model developed in ANSYS CFX. This particular case considers copper slags as filler material, allowing to simulate its behavior as a coupled solid-fluid interface system. The charging and standby phases are simulated using a coupled CFD model to capture the heat transfer mechanisms between the solid-fluid region to assess the effect of including a copper slag rock bed inside the tank. The transient temperature profile along the tank height is obtained for charging and standby process in order to analyze the thermal behavior of the rock bed during different stages in every process.

To satisfy the needs of space heating and domestic hot water, the use of renewable energies and particularly solar energy stands out for its technical feasibility and competitiveness. However, in order to mitigate the variations on the availability of the resource and fully meet the thermal loads, storage systems are commonly used. In those systems, water is usually used as heat transfer fluid, due to its low cost and thermophysical parameters that facilitate the stratification. Aiming to further this phenomenon, different geometries of inlet diffuser were proposed and assessed through computational simulations of the charging and discharging process. CFD simulations were carried out using ANSYS Fluent, aiming to compare the temperature profiles, and considering the stratification efficiency as a figure of merit. The results of the CFD simulations show that the use of the diffusers and the inlet flow through the upper zone of the tank generate the best stratification efficiencies, reducing unexpected mixing in the storage tank.