Heat transfer enhancement through sudden expansion pipe airflow using swirl generator with different angles

This investigation is aimed to study the heat transfer and pressure drop characteristics for turbulent airflow in a sudden expansion pipe (d/D = 0.72) equipped with propeller swirl generator with different blade angles. The investigation is performed for the Reynolds number ranging from 10,000 to 40,000 under a uniform heat flux condition. Three propeller fans of five blades with swirl angles theta = 15 degrees, 30 degrees, 45 degrees for upstream flow and one propeller fan with swirl angle 45 degrees for downstream flow are inserted separately inside the test section. The swirl propeller fan is located at different locations inside the tested pipe, where S = 10H, 20H and 40H for both upstream and downstream flows. The experimental results indicate that inserting the propeller upstream of the tube provides considerable improvement of the heat transfer rate up to 190% for all swirler angles with higher values obtained at theta = 45 degrees. Inserting the propeller downstream of the tube provides more improvement in heat transfer rate than inserting the propeller upstream of the tube at swirl angle of theta = 45 degrees, the heat transfer rate increased up to 225%. The maximum enhancement factor (eta) for the downstream swirler is about 326% while it is about 213% for the upstream one. Correlations for relative mean Nusselt number and enhancement factor are presented for different fan locations, swirl angles and Reynolds numbers. (c) 2012 Elsevier Inc. All rights reserved.