Experimental study on heat transfer enhancement characteristics of tube with cross hollow twisted tape inserts

This study experimentally investigates the heat transfer and friction factor (f) characteristics of a tube fitted with cross hollow twisted tape inserts of hollow widths of 6, 8 and 10 mm under uniform heat flux. Experimental data of a plain tube are compared to the standard correlations for validation. Results show that the Nusselt number (Nu) and f decrease and then increase as the hollow width increases from 6 mm to 10 mm. Nu and f for the 6 mm hollow width increase by 93%-120% and 883%-1042%, respectively, in comparison with those of the plain tube. The performance evaluation criterion (PEC) varies from 0.87 to 0.98 under a Reynolds number of 5600-18,000. Correlations based on the experimental data are established to predict Nu and f under turbulent flow. These parameters match the experimental data well within 3.6% (Nu) and 2.3% (f).