Latent thermal energy storage performance enhancement through optimization of geometry parameters

In the paper, thermal performance of vertically oriented shell-and-tube type latent thermal energy storage (LTES), which uses water as the heat transfer fluid (HTF) and RT 25 paraffin as the phase change material (PCM), has been optimized by obtaining the most favorable values of three analyzed geometry parameters; fin number, LTES unit aspect ratio and fin thickness. Optimization procedure has been performed according to two objective functions; maximization of the average latent heat flux and maximization of the LTES thermal effectiveness. Optimization of the selected set of analyzed geometry parameters for selected objectives, as well as providing optimum values of analyzed parameters for charging, discharging and the overall cycle of charging and discharging, represent the novelty of the current work since they have all been insufficiently covered in the literature. Optimization procedure has been performed using response surface methodology and the Box-Behnken design of experiment. Using the experimentally validated mathematical model and numerical procedure, the responses were obtained numerically. For each objective, responses were approximated with a regression polynomial function and the fitness of each function was assessed with the coefficient of determination R2. Optimized LTES configurations' thermal performance enhancement was evaluated through comparison with the experimental LTES thermal performance. For the LTES configuration optimized with the objective of maximizing the average latent heat flux considering the overall charging and discharging cycle, the average latent heat flux was enhanced by 32.4% during charging and by 45% during discharging. For the LTES configuration optimized with the objective of maximizing the LTES thermal effectiveness considering the overall charging and discharging cycle, the LTES thermal effectiveness was enhanced by 8.6% during charging and by 11.8% during discharging. Optimized configurations have been additionally compared with the experimental LTES configuration in terms of selected performance indicators and significant decrease in melting/solidification times have been observed. Optimization results can be used in designing more efficient LTES tanks and provide guidelines for further optimization procedures.