Computational Analysis of Heat Transfer Enhancement in a Circular Tube Fitted with Different Inserts

Abstract

Heat transfer enhancement of air flow using wire coiled of an isosceles triangular cross-section and twisted tape inserted in a tube have been investigated under turbulent flow regime. A simulation technique is employed to simulate the swirling flow with three different pitch ratios (P/D = 1,2, and 3). The isosceles triangle side length to tube diameter is (a/D = 0.2 and 0.4) and (a/D=0.93) of the twisted tape at a distance (s) of 2 mm from the tube wall for the both in the range of Reynolds number from 4000 to 20,000. The heat transfer enhancement represented by a Nusselt number (Nu) and friction factor (f) in turbulent flow regime is numerically investigated using CFD package (Ansys FLUENT) to investigate the physical behavior of the thermal and fluid flows under uniform heat-flux. The results show that the use of twisted tape and isosceles coiled wire lead to a considerable increase in heat transfer and pressure drop in comparison with the plane tube. The Nusselt number increases with the increase of triangle side length and twist width and with the decrease of pitch ratio. The highest overall enhancement efficiency of 126% and 150% are achieved for the isosceles triangle wire coil with a/D = 0.4 and twisted tape, respectively at P/D = 1 and Reynolds number of 20000.