Augmentation of Heat Transfer in the Axial Ducts of Electrical Machines with Tape Generated Swirl Flow

Experiments have been carried out in the range of 10X103<80X103 with wall heat flux 1.5X103 W/m2 to 10X103 W/m2 for forced convective flow through a 900 mm long duct formed by clamping together 0.35 mm electrical sheet steel stampings of 80 mm outer diameter and 26 mm inner diameter with and without a full length twisted tape insert. The twisted tape insert which serves as a turbu lent promoter to augment the convective heat transfer from the duct walls indicate nearly 30% increase in the Nuav for the same pumping power and wall heat flux. Experiments have also been carried out with 175.5 mm diamneter 380 m long assembled rotor having 12 axial ducts of 16 mm diameter, with and without full length swirl tape inserts. These investigations indicate substantial reduction in the temperature rise of the winding copper with the tape insertion in the ducts. As the situation of the ducts investigated represents heat transport boundaries of axial cooled electrical machines, this enhancement of heat transfer can be equated to an appropriate increase in the machine output for the same temperature rise. Such an increase in the output for a given frame size reduces the consumption of active materials like copper, electrical sheet steel and insulation and hence the weight per KW output of the machine.