EXPERIMENTAL STUDY ON HEAT TRANSFER AND FRICTION OF TURBULENT SWIRLING AIR FLOW THROUGH ABRUPT EXPANSION

Abstract

Heat transfer and pressure drop characteristics of turbulent swirling air flow through a sudden expansion pipe with different swirl angles and different sudden expansion ratios were investigated experimentally. The effect of the sudden expansion ratio, Reynolds number, vane angle and swirl generator location on the heat transfer and pressure drop were examined. The test pipe is uniformly heated and the Reynolds number ranges from 9,000 to 41,000. It was found that inserting a swirl generator inside sudden expansion pipe causes an increase in both the relative mean Nusselt number and the enhancement efficiency of the tested pipe. The enhancement efficiency increases with Reynolds number decreasing while it increases with the increase in sudden expansion ratio and vane angle. A maximum efficiency up to 405% could be achieved. Correlations for Nusselt number and friction factor for the swirl flow are obtained and the performance evaluation criterion to access the real benefits in using the swirl generators of the enhanced tube is discussed.