Study of the effect of tilting lateral surface angle and operating parameters on the performance of a vertical shell-and-tube latent heat energy storage system

In this paper, a comprehensive mathematical model is developed to study the thermal energy storage performance in vertical shell-and-tube latent heat thermal energy storage (LHTES) systems with different tilting lateral surface angles. This model integrates heat transfer in heat transfer fluid (HTF), HTF tube and phase change materials (PCM). It is validated using experimental data and then applied to investigate effects of tilting lateral surface angles on the enhancement of natural convection in the LHTES system. The results show that increasing the tilting lateral surface angle largely enhances heat transfer in the melting process whilst it has negative effects on the solidification process. The total melting time reduces by 45% as the tilting angle increases from 0° to 7°. An optimal tilting angle of 4° is identified based on the trade-off between melting and solidification processes. Furthermore, the effect of HTF operating parameters on the performance of the LHTES system is evaluated. It shows that the melting and solidification time of the LHTES system with a tilting angle 4° reduces by 22% and 8.5%, respectively, as the HTF flow Reynolds number increases in laminar and transition flow regions. However, increasing the HTF flow Reynolds number does not show significants effect under turbulent flow regions. The variation of the HTF outlet temperature is also investigated. The temperature difference between the HTF inlet and outlet is found small at all studied HTF flow rates, which indicates that assumption of the constant HTF surface temperature boundary in simulations in the literature is reasonable.