Application of a novel conical strip insert to improve the efficacy of water-Ag nanofluid for utilization in thermal systems: A two-phase simulation

In this research, hydrothermal characteristics and energy efficiency of the water-Ag nanofluid in a circular tube equipped with twisted conical strip inserts are investigated through the two-phase Eulerian-Lagrangian approach. The novel inserts under study are a combination of twisted tape inserts and conical strip inserts. Both staggered and non-staggered alignments for the strip inserts are examined. The effects of different forces including drag force, thermophoretic force, Brownian force and lift force are considered. Application of the strip inserts intensifies flow mixing and disturbance in boundary layer and therefore, increases Nusselt number and friction factor compared with the plain tube. The non-staggered alignment disturbs the boundary layer with a greater intensity than the staggered alignment, such that a completely swirling flow is developed for this configuration. The results show that heat transfer for the non-staggered alignment is higher than that for the staggered alignment, while the merit characteristic is greater for the staggered alignment. Moreover, the temperature and velocity distributions are more uniform for the non-staggered alignment. Additionally, Nusselt number augments by increasing either concentration or Reynolds number, whereas friction factor decreases with Reynolds number increment and intensifies by increasing the concentration. The nanofluid has a greater merit than pure water for utilization in this geometry. Meanwhile, the non-staggered alignment causes a more intense nanoparticle migration compared with the staggered alignment.