The objective of this paper is to introduce the subject of hear transfer augmentation by inserting a propeller type swirl generator in a circular pipe. The propeller type swirl generator creates a flow pattern which is like a decaying swirl flow. This flow pattern is observed for laminar flow. The main advantage of this type of swirl generator is that it is easy to install the device into a circular pipe. Average and local Nusselt numbers were calculated by the method explained in detail in the main text. Comparison of the local Nusselt numbers for swirl flow considered in this study and local Nusselt numbers for flow in a smooth pipe revealed that the local Nusselt number increases substantially when the swirl generator is used. The swirl related heat transfer enhancement becomes stronger as Reynolds number increases. (C) 1999 Elsevier Science Ltd.