Numerical investigation on consecutive charging and discharging of PCM with Modified longitudinal fins in shell and tube thermal energy storage

• Six elementary modified longitudinal fins are compared for consecutive charging and discharging conditions. • The performance of the modified designs is compared against that of the traditional rectangular longitudinal fin case. • Two-dimensional enthalpy-porosity computational model with natural convection melting and solidification transient simulations. • Herringbone wavy shape is recommended for showing better performance with its non-linear shape. • Convex shape and inverse tapering shape showed a decrease in performance compared to the base case. This study proposes six modified longitudinal fins in a shell and tube heat exchanger unit to see how the modification affects the charging and discharging of PCM. The proposed cases are modifications to the traditional rectangular shape (Case 1), employing a tapering shape (Case 2), inverse tapering shape (Case 3), herringbone wavy shape (Case 4), convex shape (Case 5), and constricted shape (Case 6). A two-dimensional computational model is applied by applying the enthalpy-porosity method. Transient simulations are conducted with the inclusion of the natural convection effect for melting and solidification. The influence of the proposed designs on the solid-liquid interface is evaluated by observing liquid fraction and temperature distribution. The cases are compared by the total time for phase transition and time savings percentage. It is found that Case 4 (herringbone wavy shape) stands out over all the cases in terms of total phase transition time, melting time and solidification time, showing a better performance by 10.93 %, 8.48 % and 12.31 % improvement respectively, compared to the traditional rectangular case (Case 1). On the other hand, the convex shape (Case 5) performed the worst, even decrease in percentage by 3.55 %, 5.88 % and 5.04 %, in terms of full cycle completion time, melting time and solidification time, against the base case.