The current investigation aims to study the second law features of an innovative nanofluid having hybrid nanoparticles of graphene nanoplatelets–Pt through a ribbed triple-tube heat exchanger (RTTHX). The hot nanofluid passes inside the ribbed annulus side, the cold water enters inside the inner tube side, and the normal water moves through the outer annulus side. The effects of nanoparticle weight fraction as well as geometrical parameters including the pitch and height of the ribs are evaluated. The total entropy generation rate of heat exchanger reduces by the weight fraction increase, which demonstrates the great advantage of employing the nanofluid. Both increasing the rib height and rib pitch decrement reduce total entropy production of the nanofluid, whereas increase the total entropy production of RTTHX. Moreover, the total exergy destruction of whole heat exchanger decreases by increase of the weight fraction, such that it reduces about 23% with increasing the weight fraction from 0 to 0.1% at rib pitch of 150 mm and rib height of 3 mm. Furthermore, the second law efficiency enhances with the weight fraction increment, while reduces with the rib pitch decrement and increasing rib height. The second law efficiency has great values in all conditions under study.
