Numerical evaluation of the effect of using twisted tapes as turbulator with various geometries in both sides of a double-pipe heat exchanger

In this study, the effect of using twisted tapes with various geometries in both tubes of a double-pipe heat exchanger is numerically investigated. The twisted tapes are inserted in both sides of double-pipe heat exchanger to improve the heat transfer where the fluid is water in both sides. The influence of geometrical parameters including the number of twisted tape and creating hollow on twisted tape with different aspect ratios is investigated numerically. The obtained results are analyzed by calculating the outlet temperature of both sides, pressure drop, Nusselt number, and coefficient of performance. Numerical simulations are performed by a commercial CFD code, ANSYS FLUENT 18.2. The results indicate that increasing the number of twisted tape from one-fin to four-fin leads to an increase in the Nusselt number 3.1%, pressure drop 64%, and coefficient of performance 63.9%. Eventually, based on outcomes, four-fin twisted tapes provided better coefficient of performance. In the second part of the study, the effect of creating hollow on the four-fin twisted tape with different aspect ratios (AR = W/H) is studied. Three different aspect ratios including 2.25, 1, and 0.44 are considered. The results show that creating the hollows with AR = 1 on the twisted tape leads to better coefficient of performance.