Experimental Study of Heat Transfer Augmentation Characteristics of a Tube Affected by Geometric Parameters of Coiled Spring Inserts

Abstract

In the present study, the heat transfer and flow friction characteristics of a circular tube with coiled spring inserts are experimentally reported for a fully developed turbulent flow regime. Experimental investigations were performed in a circular concentric tube in a tube heat exchanger in the Reynolds number (Re) range of 8000–32,000 with water as a working fluid. The average Nusselt number ratio (Nua/Nup) and average friction factor ratio (fa/fp) with and without inserts are reported to be in the range of 1.79–2.79 and 2.44–4.17, respectively, for the tested six geometries of the inserts. The Nusselt number ratio (Nua/Nuc) based on equal pumping power criteria is also reported and found to be in the range of 0.94–1.24. The effects of varying pitch to length of insert ratio (p/l) and diameter of insert to the inner diameter of tube ratio (dc/Di) on heat transfer and pressure drop are reported, and empirical correlation is given for Nusselt number in terms of Reynolds number (Re), pitch to length of insert ratio (p/l), insert diameter to inner diameter of tube ratio (dc/Di), and Prandtl number (Pr).

Keywords

• passive insert
• average performance ratio
• turbulent flow