Heat Transfer and Pressure Drop Characteristics of Turbulent Flow In a Tube Fitted With Conical Ring and Twisted Tape Inserts

The present work shows the results obtained from experimental investigations of the augmentation of turbulent flow heat transfer in a horizontal tube fitted with combined conical-ring turbulators and a twisted-tape swirl generator. The air is the working fluid for Reynolds number range of 5000-23000 under constant wall heat flux thermal boundary condition. In this study, two enhancement heat transfer devices are used. One is the conical-ring used as a turbulator and placed in the tested tube with constant diameter ratio (d/D=0.538) and the other is the twistedtape swirl generator placed at the core of the conical-rings. Three twisted-tapes of different twist ratios, Y=2, 3, and 6, are introduced in each run. The experimental data obtained are compared with those obtained from the plain tube and from the literature to ensure the validation of experimental results. Correlations for Nusselt number, friction factor, and enhancement efficiency are developed. It is observed that the heat transfer process enhances by using combined conical-ring and twisted-tape inserts or each one alone when compared to plain tube at the same mass flow rate, and this enhancement increases as twist ratio decreases for the case of combined insertion.