experimental study of heat transfer augmentation characteristics of a tube affected by geometric parameters of coiled spring inserts

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).