The turbulent single-phase forced convection heat transfer and pressure drop characteristics of circular ducts containing swirl-row inducers or pall rings

The heat transfer and pressure drop characteristics of tubes containing either Pall rings, or helical (180°) strips of metal, were studied experimentally. Tests were performed with water in the Reynolds number range of 11000 to 104000, approximately. Rotameters were used to measure the volumetric flowrate of the water. The effect of fluid temperature on this measurement was determined. The insertion of a continuous length of Pall rings into a tube increases the Nusselt number and pressure drop by factors of 1.5 and 15. (These factors are relative to the empty tube over the same flow range). Smaller increases were obtained while using rings that were equidistantly spaced along the tube. [Continues.]