In this study, decaying turbulent swirl flow in a cylindrical tube is investigated experimentally. The swirl is generated with an innovative helical swirl flow generator. The tube surface is maintained at a constant temperature using a constant temperature water bath. Air is used as the working fluid. Experiments are conducted in a Reynolds number range between 20,000 and 56,000. Effects of the helical swirl generator length (h = 15, 20, 25 and 30 mm) and the tube length to diameter ratio (L/D = 10, 20, 30 and 40) on the heat transfer and pressure drop are determined. It is disclosed that introducing swirl results in considerable enhancements in heat transfer, e.g. 348% for a specific test case. Effects of Re, h and L/D are found to be critically interdependent. (C) 2014 Elsevier Ltd. All rights reserved.