Performance enhancement of cylindrical latent heat storage units in hot water tanks via wavy design

Cylindrical latent heat storage units (CLHSUs) are attractive for the improvement of hot water tanks' thermal performances. However, their successful application is limited by the low conductivity of phase change materials (PCMs). In this study, a novel CLHSU geometry with a wavy side wall was proposed, with the goal of enhancing the PCM's heat transfer by effectively utilizing both close-contact melting and natural convection. Its thermal performances were evaluated based on an unconstrained melting model, and the effects of the wavelengths (Lw) and wave amplitude (aw) were analyzed. The results showed that the charging and discharging rate of the proposed CLHSU was 2.42 and 1.47 times that of the conventional CLHSU, respectively. A pure decrease in Lw would not necessarily result in the decrease in the charging time, and the shortest time would be obtained when Lw reached a threshold value for a specified aw. With the increase in aw, the average heat transfer coefficient and the total heating wall surface area increased and the charging time decreased. In the discharging process, Lw and aw exerted a negligible effect on the heat transfer coefficient, and the total surface area played an essential role in the variation of the discharging time.