The relationship between absolute vorticity flux along the main flow and convection heat transfer in a tube inserting a twisted tape

As passive enhancement devices, twisted tape insert has been used for almost a century, the most dominant heat transfer enhancement mechanism of circular tube fitted with twisted tape is the secondary flow generated by the tape. There is a parameter to specify the intensity of secondary flow, but this parameter cannot be applied to more general cases. Here cross-averaged absolute vorticity flux in the main flow direction is used to specify the intensity of secondary flow produced by twisted tape inserted in a tube. The relationship between the intensity of secondary flow and the intensity of laminar convective heat transfer is studied using a numerical method. The results reveal that the cross-averaged absolute vorticity flux in the main flow direction can reflect the intensity of secondary flow and a significant relationship between this cross-averaged absolute vorticity flux and Nusselt number exists for studied cases. The presented results validate that the cross-averaged absolute vorticity flux in the main flow direction is a general specifying of the intensity of secondary flow and can be used in other cases.