Efficacy of a new graphene-platinum nanofluid in tubes fitted with single and twin twisted tapes regarding counter and co-swirling flows for efficient use of energy

Hydrothermal attributes and energy efficiency of a new graphene-platinum nanofluid in tubes fitted with different twisted tapes are numerically investigated. The configurations under study include single twisted tape (ST), twin co-twisted tapes (CoTs) and twin counter twisted tapes (CTs) causing counter or co-swirling flows. The twin tapes generate two strong swirl flows, while the single tape creates only one swirl flow. With the concentration increment, pumping power and heat transfer augment in all configurations. Heat transfer rate of tube fitted with CTs is considerably higher than that of other configurations. Besides, the tube fitted with CoTs demonstrates highest pumping power because of greater residence time. At lower twisted ratios, swirl flows and turbulence kinetic energy are more significant and consequently, pressure drop and heat transfer rate are more intense. It is shown that particles path is longer at lower twisted ratios. Figure of merit, which shows ratio of heat transfer enhancement to pressure drop increment, is higher than unity for CTs and CoTs, and lower than unity for ST. Moreover, the twin tapes demonstrate greater merit at higher twisted ratios. Finally, it is recommended to use the CTs with higher twisted ratios to improve the heat transfer with minimum energy consumption.