Heat Transfer And Flow Resistance Characteristics Of Drag Reducing Nanofluids In The Tubes

Drag reducing nanofluids can reduce flow resistance and enhance fluid convective heat transfer. 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 graphite, multi-walled carbon nanotubes, A12O3, Cu, Al, Fe2O3, and Zn 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. Graphite and Cu nanoparticles have a better overall performance in terms of enhancing convective heat transfer and reducing flow resistance in a number of nanoparticles. 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 10 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 graphite nanofluids in a horizontal tube as well as drag reducing Cu nanofluids in the same horizontal tube and built-in twisted belt tubes were compared with final results showing the calculated and experimental values to be in good agreement. But also the error of experimental data is less than 15%, so heat transfer and flow resistance correlations have been established to further verify the reliability of experimental data.When the mass fraction of graphite and Cu nanoparticle is 0.4%, drag reducing nanofluids that they formed have the best heat transfer and drag reducing characteristics in the horizontal tube. Their overall K factor performance that is the combined effect of enhancing convective heat transfer and reducing flow resistance to drag reducing nanofluids are 5 times and 14 times larger than deionized water’s, respectively. So drag reducing Cu nanofluid has better investigation and application prospects. Then apply it into the built-in twisted belt tubes whose reverse ratio are 2.5 and 4.5, it can be found that the best mass fraction is 0.5%, at which time the effect of convective heat transfer and drag reduction reach their best performance i.e. the overall K factor performance reache maximum and they are approximately 3 times and 2 times with deionized water. Finally, in both heat transfer tubes the overall K factor performance of drag reducing Cu nanofluids 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. Meanwhile they also have a certain characteristics of reducing flow resistance.