Heat transfer and pressure drop characteristics of angled spiraling tape inserts in a heat exchanger annulus

Heat transfer augmentation in heat exchangers has received much attention in recent years, mainly due to energy efficiency and environmental considerations. Many active and passive techniques are currently being employed in heat exchangers, with twisted tape inserts providing a cost-effective and efficient means of augmenting heat transfer. This article describes how the single-phase heat transfer and pressure drop characteristics were determined for an angled spiraling tape that was inserted into the annulus of a tube-in-tube heat exchanger. Four sets of experimental measurements were taken: a normal tube-in-tube heat exchanger that was used as a reference and three heat exchangers with different angled spiraling tape inserts. Semiempirical heat transfer and pressure drop correlations were derived that predict the experimental data to within 4.3%. The angled spiraling tape inserts resulted in an increase in the heat transfer coefficients and pressure drop penalties, which varied with tape pitch and the direction of flow relative to the tape curvature. The smallest pich (25 mm) produced the greatest heat transfer enhancement (206%) and pressure drop penalty (203%). The heat exchanger with the largest pitch (100 mm) produced the lowest heat transfer enhancement (70%) and a corresponding low pressure drop penalty (58%).