Simultaneous charging and discharging of multi-tube heat storage systems using copper fins and Cu nanoparticles

In this paper, heat transfer of a multi-tube heat exchanger filled with RT82, fins, and nanoparticles is investigated using numerical modeling. There are four heat transfer fluid (HTF) tubes embedded in a shell that contains PCM. The PCM is under simultaneous charging and discharging (SCD) conditions caused by pumping two hot heat transfer fluids (HHTF) and two cold heat transfer fluids (CHTF). The arrangement of these HHTFs and CHTFs, as geometrical factors, are compared with each other. Results demonstrated that based on cold and hot tubes positioning, steady-state liquid fraction alternates between 37% and 60% as setting hot tubes at the lower half claims the maximum 60%. Fins addition results lead to the varying outcome under SCD, unlike melting cases where fin proved more practical based on liquid fraction criterion. Under SCD conditions fins show an advantage in the short time (<100 min), however, in a long time adding fins will result in less available thermal energy. Cu nanoparticles have been added into the PCM to lower the response time, however, under SCD conditions its impact is negligible. Hence, while the PCM is under SCD condition, using nanoparticles is not recommended. The results show that among different geometrical arrangements the one with inner hot tubes located at the bottom of the shell registers the most favorable outcome.