Civil and Environmental Engineering Publications

Vorticity and convective heat transfer downstream of a vortex generator

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Vorticity generation has been identified, since the 80's, as an efficient means for enhancing heat transfer; the mean radial velocity component due to the induced flow pattern contributes to the heat removal. In the present work, momentum and heat transfer are studied in a test section designed to mimic the industrial HEV (High-Efficiency Vorticity) mixer. It consists of a basic configuration with a unique vorticity generator inserted on the bottom wall of a heated straight channel. The aim of this work is to analyze to which extend the convective heat transfer is correlated to the vorticity, as it is presumed to cause the intensification. In this case, the driving vorticity is the streamwise vorticity flux Omega, and the heat transfer is characterized by the Nusselt number Nu, both quantities being spanwise averaged. The study is mainly numerical; we have used the previous PIV measurements and DNS data from the open literature to validate the numerical simulations. It is shown that there exists a strong correlation between the vorticity flux and Nusselt number close to the vortex generator. However, the axial variation diverges for these quantities when moving downstream. The Nusselt number presents a sharp peak over the VG and decreases nearly to its basic level just behind the VG, while the vortex persists far downstream from the tab and relaxes very slowly. Heat transfer intensification at the Nusselt peak is about 100%, and reduces to about 6% downstream of the VG, the intensity of the vorticity momentum being decreased only to about 50% of its peak value at the test section outlet.

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