Thermal performance of 4-lobe swirl generator under different twisted angles and β-transition using GOCuO/water and SiO2/water nanofluids

Heat transfer enhancement has been the target outcome of many researchers in the thermal engineering application. A lobed swirl generator has been applied in the application of fluid flow due to its ability to produce a high swirl intensity and reduce the pressure drop when placed before a smooth channel. It is worth mentioning that no study has been reported to have performed the enhancement by combining both the lobed swirl generator and its transition parts with hybrid and single nanofluids in a thermal application. A lot of studies have proved that swirl flow techniques come with an increase in the penalty pressure drop. Therefore, the phenomena of lobed swirl generators in reducing the pressure loss have to be considered in order to identify unique methods to increase heat transfer with an acceptable level of pressure drop as a crucial factor in determining the pumping power and eventual cost. In addition, exploring the thermal characteristics of this device for more understanding is the motivation behind this study. In the present work, the thermal performance of a four- lobed swirl generator was investigated numerically and experimentally under different parameters such as twisted angles (ranging from 90o to 450o), transition multiplier values (ranging from n = 0.25 to 0.75 mm), and variable helix dimensions (t = 0.5 to 1.5 mm). The working fluids adopted are water, different nanofluids, including SiO2, Al2O3, and CuO, with volume concentrations ranging from 1% to 5% in water and hybrid nanofluid GO-CuO/water with volume fractions varying from 0.15% to 0.75% under different Reynolds numbers (ranging from 15,000 to 55,000). The turbulence swirling flow is modelled using the shear-stress transport (SST) k-ω model. According to the obtained results, the lobed swirl generator at (θ =360) and beta transition of (n = 0.5 mm) and (t =1 mm), the heat transfer and pressure loss increase compared with plain tube by 28.78 % and 17.35 %, respectively; and by reducing the value to (n = 0.25 mm), a slight increase in heat transfer and pressure loss in the percentage by 40.32 % and 17.89 %, respectively are observed. A maximum heat transfer and pressure drop of 49-59% and 33-45% were obtained with SiO2/water with a volume concentration of 5% and a Reynolds number of 15,000. The heat transfer and pressure drop experimental results showed a maximum improvement of 65-78.57% and 36- 47%, respectively, at Reynolds number 15,000 and a volume fraction of 0.75%. Finally, the study proposed a novel empirical correlation related to the thermal conductivity experimental data of GO-CuO/hybrid nanofluid.

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