Experimental study of passive heat transfer enhancement in a drag-reducing flow

Drag and heat transfer reduction were examined in a fully developed two-dimensional drag-reducing flow with different concentrations of surfactant additives. A row of low-profile mixers was used to enhance heat transfer in the flow. The effect of the low-profile mixers on heat transfer enhancement was examined in terms of the local Nusselt number for the surfactant concentration of 90 ppm. A comparison of the cases with and without low- profile mixers show that the average Nusselt number is enhanced by about 170% for Reynolds numbers of 7000, 12000, and 16200 with only a small pressure drop penalty. This increase in heat transfer performance might be related to the longitudinal vortices generated by the low-profile mixers, resulting in the enhancement of the bulk exchange of fluid between the main flow and the near-wall region. It was found that the enhancement of the low- profile mixers to the heat transfer rate starts to deteriorate in the streamwise direction at a certain location downstream of the mixers. The location of the onset of the deterioration shifts downstream with an increase in the Reynolds number.