Heat Transfer Enhancement of Nanofluid Flow in a Tube Equipped with Rotating Twisted Tape Inserts: A Two-Phase Approach

Abstract

Al2O3–water nanofluids along with stationary and rotating twisted tape inserts are used to increase the rate of heat transfer in a plain tube. The simulations are conducted through varying the design parameters including angular velocity of twisted tape, Reynolds number and nanofluid volume concentration. It is found that inserting a twisted tape inside a tube substantially increases the heat transfer coefficient and friction factor compared to the plain tube. Compared to the stationary twisted tape, the rotating twisted tape exhibits a great potential to modify the average Nusselt number by about 32.8–39.6% at Reynolds number of 250, depending on the angular velocity. This is attributed to the formation of conical tornado-shape structures in the flow pattern, causing more effective mixing in the flow. By increasing the Reynolds number, the enhancement in the average Nusselt number increases in stationary and decreases in rotating configurations compared with the plain tube. To assess the tradeoff between heat transfer enhancement and pressure loss penalty, the performance evaluation criterion (PEC) is calculated. The results suggest that the highest PEC is obtained at Reynolds number of 250, nanofluid volume concentration of 3% and the highest studied angular velocity.