Thermo-hydraulic Performance of a Circular Tube with Perforated and Slotted Conical Ring Inserts

The present work deals with the investigation of heat transfer and friction in a circular tube fitted with solid conical ring inserts, perforated conical ring inserts and slotted conical ring inserts. The experiments have been carried out with different types of conical inserts having twist ratio of 2, 4, 6 and 8 by varying the Reynolds number between 4,000 and 12,000 using water as a working fluid. The experimental data have been collected in terms of outlet temperature, inlet temperature, wall temperature, volume flow rates and pressure drop across the test section. The maximum enhancements in Nusselt number and friction factor for solid conical ring inserts, perforated conical ring inserts, and slotted conical ring inserts are respectively 4.17 and 6.95, 3.86 and 5.48, 3.01 and 3.52 times that of a plain tube. The Nusselt number and friction factor increase with the decrease in pitch ratio, however, an increase in a number of holes as well as slots mitigates the friction factor at all the values of Reynolds number. The maximum value of thermo-hydraulic performance is found to be 2.18 for solid conical ring inserts.