Experimental study of heat transfer enhancement in a drag-reducing two-dimensional channel flow

In this paper, drag reduction and heat transfer enhancement were studied in a fully developed two-dimensional water channel flow. Surfactant solutions at different concentrations, namely 30, 70, 80 and 90 ppm, were used to examine the influence of surfactant additives on the skin friction drag and heat transfer coefficient. The magnitudes of the maximum achievable drag reduction at the above four different surfactant concentrations are about 7%, 30%, 50% and 55%, respectively. The present results show that there is no heat transfer reduction when 30 ppm of surfactant is added to the flow. With the increase of surfactant concentration to 90 ppm, heat transfer rate was reduced by about 55%. The critical Reynolds number for loss of heat transfer reduction increases with the increase of surfactant concentration. The effect of the low-profile vortex generators on heat transfer rate was examined for the surfactant concentration of 90 ppm. The results show that the averaged Nusselt number is enhanced by 180%, 160% and 150% for the Reynolds numbers of 7000, 12,000 and 16,200, respectively, as compared with that obtained in the surfactant solution without the use of vortex generators and yet the pressure drop penalty for heat transfer enhancement is rather small.