The heat transfer and friction characteristics of a decaying swirl flow were investigated experimentally. The swirling motion of the air was produced by a radial guide vane swirl generator. The vanes of the swirl generator were designed to be adjustable to obtain different swirl intensities. Different guide vane angles (15, 30, 45, 60 and 75 degrees) were used for the swirling flow experiments. The results were correlated in the form of Nusselt number as a function of Reynolds number, Prandtl number and the vane angle as Nu = 0.133Re(0.65)Pr(0.4)(1 + tan 0)(0.406). An augmentation of up to 98% in Nusselt number was obtained in the decaying swirl flow depending upon the Reynolds number and the vane angle. It was found that the performance of swirling flow is higher than corresponding axial flow with high vane angles and relatively low Reynolds numbers. (C) 1999 Elsevier Science Ltd. All rights reserved.