Heat transfer and friction factor of multi-walled carbon nanotubes-Fe3O4 nanocomposite nanofluids flow in a tube with/without longitudinal strip inserts

The heat transfer and friction factor characteristics of multi-walled carbon nanotubes-Fe3O4 (MWCNT-Fe3O4) nanocomposite nanofluids flow in a tube with longitudinal strip inserts were studied experimentally. The MWCNT-Fe3O4 nanocomposite was synthesized by in-situ growth and chemical co-precipitation method and characterized by various techniques; after that stable nanofluids were prepared by dispersing MWCNT-Fe3O4 in distilled water. The heat transfer and friction factor experiments were conducted for nanofluids in the Reynolds number from 3000 to 22,000, volume concentrations from 0% to 0.3%, and longitudinal strip inserts of aspect ratios 1, 2, 4 and 12. The maximum Nusselt number and friction factor enhancements were observed for 0.3% nanofluid flow in a tube with longitudinal strip insert of aspect ratio 1. From the results, the Nusselt number enhancement for 0.3% nanofluid flow in a tube without inserts is 32.72% and with inserts of aspect ratio 1 is 50.99% at a Reynolds number of 22,000. Similarly, friction factor enhancement for 0.3% nanofluid flow in a tube without inserts is 1.15-times and with inserts of aspect ratio 1 is 1.26-times for a Reynolds numbers of 22,000 compared to base fluid. A new Nusselt number and friction factor regression equations were proposed based on the experimental data.