The heat transfer enhancement of the converging-diverging tube in the latent heat thermal energy storage unit: Melting performance and evaluation

Latent heat thermal energy storage (LHTES) has emerged as a promising approach to settle the intermittent and fluctuant of renewable energy but heat transfer enhancement is necessary due to the low thermal conductivity of the phase change material (PCM). This study numerically investigated the heat transfer enhancement effect of the typically converging-diverging tubes (CDTs) inside a shell-and-tube LHTES unit. The evolution of melting behavior was analyzed to describe the heat transfer enhancement mechanism of the CDT. Based on the enhancement effect and pump power consumption associated with the CDT, a modified performance evaluation criterion (PEC) was established to evaluate the feasibility of current designs. The arrangement of CDTs was found to significantly improve the heat transfer performance of LHTES. The triangle CDT exhibited the maximum melting time reduction of 20.77%. The heat transfer enhancement effect of CDT was attributed to the enhanced natural convection of PCM and forced convection of heat transfer fluid. The analysis of the evaluation ensures the feasibility of the new criterion and its specific application field. Moreover, it was worth to note that the triangle CDT achieved the best cost performance of 0.363 ω, where ω represented the return factor. •Converging-diverging tubes (CDTs) significantly enhance heat transfer in LHTES.•A modified performance evaluation criterion (PEC) is established for the evaluation.•CDTs improve both natural and forced convection in LHTES.•The optimal arrangement triangle CDT reduces the melting time by 20.77%.•The triangle CDT exhibits the best cost performance among studied configurations.