An investigation of heat transfer characteristics of swirling flow in a 180° circular section bend with uniform heat flux

An experiment was performed to obtain the local heat transfer coefficient and Nusselt number in a circular duct with a 180degrees bend for Re=6 X 10(4), 8 X 10(4) and I X 10(5) under swirling flow and non-swirling flow conditions. The test tube with a circular section was made from stainless steel having a curvature ration of 9.4. Current beat flux of 5.11 kW/m(2) was applied to the test tube by electrical power and the swirling motion of air was produced by a tangential inlet to the pipe axis at 180degrees. Measurements of local wall temperatures and the bulk mean temperatures of air were made at four circumferential positions at 16 stations. The wall temperatures showed a reduced distribution curve at the bend for the non-swirling flow, but this effect did not appear for the swirling flow. The Nusselt number distributions for the swirling flow, which was calculated from the measured wall and the bulk temperatures, were higher than that of the non-swirling flow. The average Nusselt number of the swirling flow increased by about 90-100%, compared to that of the non-swirling flow. The Nu/Nu(DB) values at the 90degrees station for non-swirling flow and swirling flow were approximately 2.5 and 4.8 at Re=6 X 10(4) respectively. The values agree well with Said's results for non-swirling flow.