This experimental study addresses the entropy generation in a circular tube with coiled-wire inserts. The wire inserts were manufactured with an equilateral triangular cross-section and were coiled using a method so that an edge of the triangle was oriented to face the flow direction. The triangle side length of 4, 5 and 6 mm were chosen for the experiment. The coiled-wire inserts were installed with 1, 1.5 and 2 mm separations from the inner tube wall and coiled with three different pitch-to-diameter ratios: P/D = 1, P/D = 2 and P/D = 3. A uniform heat flux was applied to the outer surface of the tube. Experiments were performed for a range of Reynolds numbers from 2731 to 27,732. The effect of several conditions on entropy generation were studied. The experimental results revealed that entropy generation number increases with increasing of Reynolds number and decreases with increasing pitch ratio. The thinner wire configuration's entropy generation numbers were lower than the other models. The entropy generation number was quite closer to each other in terms of separation between inner wall of the tube and the wire inserts. The minimum entropy generation was obtained for the tube-and-insert combination with s = 2 mm, e = 4 mm and P/D = 3. (C) 2017 Elsevier Ltd. All rights reserved.