Improved heat transfer and flow resistance achieved with drag reducing Cu nanofluids in the horizontal tube and built-in twisted belt tubes

Experimental studies were performed to investigate drag reducing nanofluids' convective heat transfer coefficient and flow resistance coefficient at Reynolds numbers ranging from 2000 to 18000. Added 0-0.5% mass fraction of Cu nanoparticles into a concentration of 100-400 mg.kg(-1) cetyl trimethyl ammonium chloride (CTAC), which is a drag reducing fluid. The ratio of two kinds of fluids was explored to find a suitable composition and preparation to define their overall convective heat transfer and flow characteristics. Results indicated that the addition of sodium salicylate (Nasal) in CTAC with deionized water creates an improved drag reducing fluid with stability. When the drag reducing fluid concentration reached 200 mg.kg(-1), it reached its optimum drag reducing performance in horizontal tube experiments. Experiments with built-in twisted belt tubes resulted in a much improved convective heat transfer characteristic. Results showed using drag reducing Cu nanofluids the heat transfer coefficient will be approximately twice as large as that found in a horizontal tube and the flow resistance coefficient is approximately ten times greater. However, even though built-in twisted belt tubes can enhance heat transfer, they also increase flow resistance. Heat transfer and flow resistance correlations of the drag reducing Cu nanofluids in a horizontal tube and built-in twisted belt tubes were compared with final results showing the calculated and experimental values to be in good agreement. When Cu nanoparticle mass fraction is 0.4%, drag reducing Cu nanofluid has the best heat transfer and drag reducing characteristics. Finally, the overall K factor performance were greater than 1 at different concentrations, which indicated their convective heat transfer enhancing effect was stronger than the reducing flow resistance effect so that they can be used to solve the problem of heat transfer deterioration for drag reducing fluids. (C) 2015 Elsevier Ltd. All rights reserved.