Heat transfer assessment of turbulent nanofluid flow in a circular pipe fitted with elliptical-cut twisted tape inserts

Abstract

In the present work, a numerical study is conducted to improve the thermal performance of a circular pipe fitted with the elliptical-cut twisted tape (ECT) inserts in presence of a nanofluid as the working fluid. A comparison between the pipe with and without ECTs in different cases is implemented. This investigation is accomplished for a 3D periodically turbulent flow with constant heat flux on the walls. The effect of inserting the ECTs with different parameters, namely the ratio of short diameter to twisted tape width (WA = a/W = 0.7, 0.8, 0.9) as well as the ratio of long diameter to short diameter of the twisted tape (BA = b/a = 2, 2.5, 3) is examined. In the case of WA = 0.7 and BA = 2 for Reynolds number of 7000, the Nusselt number and thermal efficiency factor (TEF) are maximum with the values about 117.25 and 1.392, which show 6.18% and 6.6% improvement compared to the case with the square-cut twisted tape. Moreover, the Cupric Oxide nanoparticles-enhanced fluid with the nanoparticle concentration ranging from 1 to 4% is used to study the effects of the nanofluid on the heat transfer performance of the different configurations. Based on the results, the highest Nusselt number and TEF occur at the concentration of 4%, which are equal to 177.81 and 1.7637, respectively. Moreover, the TEF for the case with the elliptical-cut twisted tape and nanofluid is 21% higher than the same geometry with water as the working fluid, and 26% higher than the square-cut twisted tape in the presence of water.