Abstract
The thermal performance of high-Prandtl-number Fe3O4–vacuum pump oil (VPO) nanofluid with wire coil (WC) inserts is experimentally studied under laminar flow conditions. The volume concentrations of the nanoparticles considered are 0.05, 0.2, and 0.5%. The study also investigates different values of the ratio of the pitch to diameter (p/di) of the WC inserts; those include 1.79, 2.54, and 3.24. Mass flow rates of the base fluid and the nanofluids considered in the experimental tests are 0.0416, 0.083, 0.12, 0.166, and 0.208 kg/s, and their corresponding Reynolds numbers are 63.3, 126.6, 189.9, 253.2, and 316.5. The results show that heat transfer enhancement is increased as the particle volume concentration increases. Also the results show that the heat transfer process can be improved with the use of WC inserts, and this improvement becomes higher at smaller p/d ratio values. For instance, when 0.5 vol.% of nanofluid flows in a tube with a WC insert of p/d=1.74, the Nusselt number increases by 20.52% over that of a plain tube. It was also found that the presence of nanoparticles and the use of the WC insert increase the pressure drop, causing the friction factor to increase. The study found that the combined effect switches in favor of using the WC inserts and Fe3O4–VPO nanofluid because the resulted heat transfer enhancement outweighs the increase in the friction factor.