Second law analysis of a hybrid nanofluid in tubes equipped with double twisted tape inserts

Abstract

Entropy generation rates for flow of a novel hybrid nanofluid containing graphene–platinum nanoparticles in tubes equipped with double twisted tapes, which can develop diverse swirling flows, are analyzed based on the second law of thermodynamics. The twisted tapes under study include double co-twisted tapes and double counter twisted tapes with various twisted ratios. Based on the obtained results, using the double counter twisted tapes is recommended since they demonstrate the lower entropy generation rate (i.e. smaller overall irreversibility) compared with the double co-twisted tapes. The double counter twisted tapes are able to create more intense swirl flows, disturb boundary layer and reduce total entropy generation rate more than double co-twisted tapes. Smaller irreversibility for the double counter twisted tapes is a pleasant outcome based on the second law of thermodynamics. Furthermore, using lower twisted ratios is suggested since although with the twisted ratio reduction, the frictional entropy generation augments, the thermal entropy generation reduces and due to dominance of thermal entropy generation, total entropy generation decreases. In the case of double counter twisted tape, the global thermal entropy generation rate reduces around 10% with decreasing the twisted ratio from 3.5 to 2.5 at concentration of 0.06%. Moreover, the results reveal that using the nanofluid instead of the base fluid decreases total entropy generation and consequently overall irreversibility. Indeed, adding the graphene–platinum nanoparticles, even in low concentrations, profoundly reduces the thermal entropy generation while the frictional entropy generation increases slightly. Thereby, in the case of double co-twisted tapes with twisted ratio of 3, increasing the concentration from 0% to 0.1% causes 14% decrement in the global thermal entropy generation.