On heat transfer enhancement in swirl pipe flows

We propose theoretical model of the heat transfer in the axisymmetric swirl pipe flows. The model is used to study influences of the type of vortex symmetry and of the vorticity distribution in the vortex core on the heat transfer enhancement. The study shows that traditional empirical correlations for swirl flows are, in general, insufficient. Indeed, two types of vortex structures can exist in the swirl flows with the same integral characteristics: vortices with left-handed and right-handed helical symmetry. Left-handed helical vortexes generate wake-like swirl flows and increase heat transfer in comparison with the axial flow. Right-handed vortex structures generate jet-like swirl flows and can diminish heat transfer. Two major factors of the heat transfer enhancement have been identified: (i) formation of the swirl flow with left-handed helical vortex; (ii) modification of the near wall velocity profile of the inviscid flow due to the different vorticity distribution in the vortex core.