This investigation is aimed at studying the heat transfer characteristics and pressure drop for turbulent
airflow in a sudden expansion pipe equipped with propeller type swirl generator or spiral spring with
several pitch ratios. The investigation is performed for the Reynolds number ranging from 7500 to
18,500 under a uniform heat flux condition. The experiments are also undertaken for three locations
for the propeller fan (N = 15 blades and blade angle of 65) and three pitch ratios for the spiral spring
(P/D = 10, 15 and 20). The influences of using the propeller rotating freely and inserted spiral spring on
heat transfer enhancement and pressure drop are reported. In the experiments, the swirl generator
and spiral spring are used to create a swirl in the tube flow. Mean and relative mean Nusselt numbers
are determined and compared with those obtained from other similar cases. The experimental results
indicate that the tube with the propeller inserts provides considerable improvement of the heat transfer
rate over the plain tube around 1.69 times for X/H = 5. While for the tube with the spiral spring inserts, an
improvement of the heat transfer rate over the plain tube around 1.37 times for P/d = 20.