Optimizing diverse triplex-tube heat storage systems with composite phase change materials in simultaneous charging and discharging environment

In this study, the thermal performance of triplex-tube heat storage system consisting of RT55 phase change material and Cu metal foam composite was investigated to find out the most efficient configuration among 17 distinct models (M1-M17) categorized into 4 distinct classes. Under simultaneous charging and discharging conditions, the melt fraction and latent heat storage capacity were calculated and finally an enhancement parameter was formulated. Additionally, the multi-criteria decision-making methods such as Analytical Hierarchy Process (AHP) and Technique for Order Performance by Similarity to Ideal Solution (TOPSIS) were employed to obtain preference-based optimized designs. The findings revealed that model M7 has the highest steady melt fraction of lambda ss = 0.81 with 107% enhancement among the models having equal volumes of PCM and composite PCM, i.e., M3-M8. The fin-type model M13 and rhombus-type model M14 provide the larger space for enhanced convection that leads to a high steady-state melt fraction values of lambda ss = 0.71 and 0.75, respectively. In addition, both AHP and TOPSIS techniques predict model M13 as the optimized choice among all models upon considering the equal weightage criteria for the steady-state melt fraction (lambda ss), steady-state time (tss), and rate of steady latent heat stored per unit cost (L*).