Influences of fin shape, operational temperatures, and loading of spheroidal graphene nanoplatelets on the cyclic performance of the latent heat storage system

Adopting a multi-factor enhancement technique is currently one of the most efficient ways to improve the cyclic performance of a latent heat thermal energy storage system. This paper explores the effects of the fin configuration, charging operating temperature, and loading of graphene nanoplatelets with the discharge temperature on energy storage and discharge performance improvement. The preliminary investigation explores the impacts of fin configuration and charging temperature on cyclic performance. The study examines three distinct fin shapes, namely straight, single cross, and double cross, and four inlet charge temperatures of 75, 80, 85, and 90 °C. Afterward, the effects of adding graphene nanoplatelets to the pure phase change material (PCM) (up to 3 vol%) and varying the discharge water temperature on the system's performance improvement are studied. The enthalpy-porosity methodology is adopted to establish a 3D computational model for studying the effects of these parameters on the melting and solidification dynamics of paraffin wax that is used as a PCM. The results indicate that the double cross fin exhibits the most rapid melting and solidification rates, along with superior daily performance. This configuration demonstrates a reduction in melting, solidification, and overall cyclic times by 35.9 %, 35.2 %, and 35.6 %, respectively, compared to the longitudinal fin. In contrast, the single cross fin unit realizes reductions of 22.8 %, 21.9 %, and 22.4 % in these times, respectively, when compared to the longitudinal fin. The single and double cross fin units improve the daily charging capacity by (23.3 % and 45.9 %), charging rate by (23.5 % and 46.5 %), daily discharging capacity by (20.5 % and 39.7 %), discharging rate by (19.7 % and 38.6 %), charging effectiveness by (16.9 % and 31.7 %), and discharging effectiveness by (23.9 % and 46.1 %), respectively, compared to the longitudinal fin. The highest inlet charge temperature lowers the total cyclic time by 32.8 %, improves the daily charging and discharging capacity by 32.6 %, improves charging effectiveness by 3.8 %, and increases the number of complete cycles by 18.8 %. Adding graphene nanoplatelets up to 3 vol% and lowering the discharge temperature to 16 °C reduces the total cyclic time by 44.5 %, improves the daily charging and discharging capacities by 101.6 % and 83.3 %, and improves the average effectiveness by 43.4 % for charging and by 63.8 % for discharging. The results obtained provide valuable insights for the design and development of thermal energy storage systems utilized in solar heating applications.