Mehdi Bahiraei

The current paper attempts to numerically examine the hydrothermal characteristics and energy performance of a hybrid nanofluid containing graphene nanoplatelet–platinum composite powder in a triple-tube heat exchanger equipped with inserted ribs. The nanofluid flows in the inner annulus side, whereas the cold water and normal water flow in the tube side and outer annulus side, respectively. The ribs are installed on the outer surface of the inner tube. The overall heat transfer coefficient, effectiveness and heat transfer rate of the heat exchanger are enhanced by increasing the nanoparticle concentration and rib height and by decreasing the rib pitch. The pressure drop is more intense in the cases of smaller rib pitch and higher rib height because the particles pass longer routes under these conditions. Based on the heat transfer enhancement, the case with greater rib height and smaller rib pitch at the highest concentration is suggested, because demonstrates the greatest thermal performance for the heat exchanger. Whereas, in the view of the energy efficiency, the heat exchanger with the smaller rib height and lower rib pitch with the highest nanoparticle concentration is recommended since the performance index of this case is greater than that of the other cases.