Design of thermal energy storage unit for Compressed Air Energy Storage system

The aim of this paper is to present a new concept of a high-temperature thermal energy storage (TES) for the application in the compressed air energy storage (CAES) systems. The proposed storage unit combines the advantages of pressurized containers with packed beds, e.g. of rocks, with the strengths of non-pressurized systems such as those encountered in CSP plants. Designed TES unit consists of the heat exchanger located inside a high-temperature thermocline-type vessel with molten HITEC (R) salt used as a heat storing material. In terms of the geometry of the designed heat exchanger, a tube-in-tube helical coil type was chosen due to its higher convective heat transfer coefficients in comparison with straight tubes. To find the most suitable case, four helical coils with different dimensions (diameter, pitch) were considered. Heat transfer and pressure drop analysis for each configuration were conducted. In particular, convective and overall heat transfer coefficients as well as friction factors were computed based on the empirical correlations. To verify the obtained results, the analysis based on numerical approach has been carried out with the use of ANSYS Fluent software for the most suitable case.