In this study, heat-transfer and pressure-drop characteristics of a decaying swirl flow in a horizontal pipe are investigated experimentally. The decaying swirl flow is produced by the insertion of swirl generators with propeller-type geometry, a kind of passive heat enhancement tools. Three different positions of the swirl generator in the axial direction are examined: at the inlet (x = 0), x = L/4 and x = L/2. For each position, the effects of the vane angle about the core of the insert device and the number of vanes attached circumferentially to the device on heat transfer and pressure drop are studied. Experiments are conducted at Reynolds numbers ranging from 5000 to 30,000. The optimum geometry is determined according to the exergy analysis and the performance evaluation method used.