Thermohydraulics of TiO 2 /Water Nanofluid in a Round Tube with Twisted Tape Inserts

The influence of TiO 2 nanoparticles with different volume concentrations in water on heat transfer, friction and thermal performance is explored, and finite volume method is used to clarify the heat transfer in a tube inserted with twisted tape (TT). In the experiment, swirling tubes are generated by TT insert with the twisted ratio (y/w) of 3.0 in the range of Reynolds number between 5400 and 15,200. The mathematical modeling which involves the prediction of flow behaviors in a tube is also conducted. The concentration of nanofluid (ϕ) was varied from 0.07 % to 0.21 % by volume. The results revealed that TiO 2 nanoparticles suspended in water enhanced thermal conductivity, and movement of TiO 2 nanoparticles delivered energy exchange. Although an increase of TiO 2 concentration led to an increase in friction due to small particles suspending in fluid, the heat transfer and thermal performance could enhance significantly. As compared to pure water, the presence of TT with TiO 2 nanoparticles at ϕ = 0.07 %, ϕ = 0.14 % and ϕ = 0.21 % indicated a 0.7 %, 1.7 % and 3.1 % higher thermal performance, respectively. With a higher Reynolds number, the thermal performance would be less pronounced due to high flow friction. From the experimental results, the understanding in relation to the effects of TiO 2 concentration and Reynolds number on Nusselt number (Nu), friction factor (f) and thermal performance factor (η) is presented for a wide range of thermophysics and heat transfer application.