Thermal behaviour of latent thermal energy storage unit during charging and discharging processes: effects of HTF inlet velocity

In order to study the transient thermal behaviour of a shell-and-tube latent thermal energy storage (LTES) unit using phase change material (PCM) under variable heat transfer fluid (HTF) inlet velocities, a mathematical model based on the enthalpy formulation was developed and numerically investigated using a computational fluid dynamic. The effects of HTF inlet velocity on the transient thermal behaviour of the unit in term of PCM temperature and melting fraction evolution, as well as the unsteady total energy stored evolution are determined. The results show that charging and discharging processes have three periods for the change of temperature regarding to time in PCM: rapidly changing period, no changing period and slowly changing period. The whole LTES process during the two cycles can be divided into three periods for the change of melting fraction regarding to time in PCM: the first is sensible heat charging/discharging period; the second is latent heat charging / discharging period and the third is sensible heat charging / discharging period again. Increasing the HTF inlet velocity slowly increases the temperature and melting fraction evolution. The total energy stored gradually increase from minimum value to maximum value defined the end of the process; the amount of total energy stored under different HTF inlet velocities is the same, except the time needed for completing charging or discharging processes