Thermo-hydraulic performance of a biological nanofluid containing graphene nanoplatelets within a tube enhanced with rotating twisted tape

In this study, thermo-hydraulic performance of an ecofriendly nanofluid containing graphene nanoplatelets is examined within a tube enhanced with rotating twisted tape. The variable parameters consist of rotational speed, twisted ratio (lambda), and nanoparticle weight fraction, which their influences are evaluated. It is found that the convective heat transfer coefficient and pumping power augment by increasing the rotational speed and weight fraction, while decrease by increasing the twisted ratio. Moreover, Figure of Merit (FoM), which indicates merit of using the rotating twisted tape, has values higher than 1 at all cases under study. The maximum value of FoM (i.e., 1.6) occurs at lambda = 2.5, weight fraction of 0% and rotational speed of 900 rpm. Based on the obtained results, equipping the tube with the rotating twisted tape is greatly recommended, especially at high rotational speeds because it generates severe swirl flows, intensely disrupts the thermal boundary layer and significantly improves the cooling performance with reasonable pumping power increment. In addition, employing the graphene sheets based nanofluid is suggested as the working fluid since the rotating twisted tape along with the nanofluid is more effective than that together with the base fluid, which is due to the excellent thermal conductivity of graphene sheets. (C) 2019 Elsevier B.V. All rights reserved.