Experimental investigation of heat transfer and pressure drop inside elliptic tube with inserted helical coils

The paper deals with an experimental study of the influence of varying helical coil cross section diameter and pitches of helical coil on heat transfer and friction characteristics in an elliptical tube. The present work studies the effects of copper helical coils of circular cross section formed with different diameters of 2 and 6 mm at varying pitches (20, 45, 135 and 225 mm) inside elliptic tube. In the experiments, cold air at ambient condition is passed through the uniform heat flux circular tube for Reynolds numbers in a range of 11000 to 37500. The experimental results demonstrate that the use of helical coil inserts in elliptic tube leads to a higher heat transfer rate than that of the plain surface tube. Also, increasing helical coil cross section diameter and decreasing pitches of the helical yield a better heat transfer than the plain tube. The enhancement efficiencies of the helical coil cross section 6 mm over wire cross section 2 mm diameter at a pitch of 20 mm is 2.3% at Re=11000. The results are also correlated in the form of Nusselt number, friction factor and enhance efficiency as a function of Reynolds number, pitches and diameter of helical coil