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.