Melting and solidification within an energy storage unit with triangular fin and CuO nano particles

•CuO nanoparticles were dispersed in paraffin to improve thermal feature.•Solidification and melting of RT35 have been simulated.•Impose of triangular fins can enhance solidification rate about 40.75%.•Temperature augments about 5.81% as time increases from 1 to 5 min for melting case. In this attempt, the heat stored and released units with combination of copper oxide (CuO) nanoparticles and triangular fin on the process of charging and discharging in the triplex pipe has been scrutinized. The middle tube is full of RT35 and CuO was dispersed to enhance its conductivity. Water flows via the outer and inner tube. Impacts of combining nanoparticles and fin on the period of various times of the Phase Change Material (PCM) solidification and melting process were scrutinized. The outputs depicts that the existence of nanoparticles reduces the discharging process as well as melting phenomena. The results indicate that impose of triangular fins can enhance solidification rate about 40.75% and with inclusion of nanoparticles, solidification time declines about 44.88%. Temperature of PCM at end of discharging declines about 13.34% when φ = 0.02. As fraction of nanofluid augments, melting time declines from 5.616 min to 5.4 min. Temperature of PCM augments about 5.81% as time increases from 1 to 5 min for melting case. Stored energy is an increasing function of time during melting while augments of φ leads to reduction of this factor.