Evaluation of the energy transfer process in a thermal storage device with a high-temperature working fluid during its discharge

Thermal energy storage technologies can improve the stability of production and consumption of traditional and renewable energy. The article presents the design of a thermal energy storage device, which is proposed for integration into a distributed energy system as a tool for regulating fluctuations in electricity production and consumption. The principle of its operation and scope of application are described. The aim of the work is to study the process of energy transfer in a thermal storage device during its discharge. A method for evaluating the discharge of a thermal energy storage device with a high-temperature working fluid has been developed. The developed calculation algorithm is presented, which allows calculating the geometric dimensions of the energy storage and the time of its discharge. The assessment of the discharge of the thermal energy storage is implemented by calculating and comparing several stationary operating modes of the thermal energy storage, characterized by different temperatures of the heat accumulator, which for each subsequent mode is reduced by a set step 100 °C. Analysis of the results showed that at high temperatures, the dominant mechanism of heat transfer is radiant emission, the proportion of which gradually decreases with the decrease in temperature of the insulation layers. With the decrease in temperature, the share of convective losses increases, estimated through an equivalent thermal conductivity coefficient. Exponential expressions have been obtained to describe the decrease in the temperature of the outer wall and the proportion of the residual charge of the thermal energy storage over the time of its operation. Comparing different stationary modes has allowed an estimation that over 72 hours, the thermal energy storage discharges up to 26.7 % (the temperature of the accumulator drops from 2000 to 700 °C).