Numerical modeling of heat transfer in the fixed-matrix regenerator working in the Electric Thermal Storage heating system

The study presents the concept of Electric Thermal Storage (ETS) central heating system. Thermal Energy Storage (TES) is carried out in the fixed-matrix regenerator. The energy conservation equations, determined for the discharge period of the regenerator operation, are implemented in MATLAB numerical procedures based on the Finite Volume Method (FVM). In the model pressure drops within the system are calculated, both for the airflow through the inner tubes, and between the tubes. The flow distribution calculations show that the assumption of even air flow distribution would not be justified. Subsequently, the values of heat transfer coefficients are determined for the four distinct heat transfer surfaces, for the variable axial coordinate z and during the time of the system operation. The use of two different criterion equations is considered, for determining the mean Nusselt number Num for fluid flow through the concentric annular duct, as well as for the local Nusselt number Nuz calculated for the fluid flow through a circular or non-circular ducts. The most appropriate approach is selected by comparing the calculation results with experimental data. Taking into account the relative error, RMSE, and MAPE values calculated, it may be concluded that the Taler correlation – for non-circular ducts – gives results closer to the experimental data obtained