Twisted tape variable wavelength effect on nanofluid flow and heat transfer inside elliptical shape tube

In this investigation, fluid flow and heat transfer in a tube having circular and elliptical shapes are studied numerically. Using twisted tapes with constant and variable wavelengths along the flow on the flow field and heat transfer is investigated. The governing equations are solved with the finite volume method. The accuracy of numerical results in the turbulent flow simulation is assessed by validating and comparing the numerical results with the available experimental data. MWCNT/water nanofluid was used to enhance the heat transfer. The influence of volume fraction of nanoparticles on flow behavior and heat transfer in the presence of the twisted tape was studied. The tube shape (circular and elliptical shape with aspect ratios of 0.6 and 0.8), Reynolds number (from 4000 to 16,000), twisted tape wavelength (0.1 and 0.2), and the nanoparticles volume fraction (from 0.005 to 0.03%) are the independent parameters. The obtained numerical results showed that modifying the tube’s shape to elliptical and increasing the number of tape twists increase the heat transfer and friction coefficient. According to the results, in the flow with the maximum Reynolds number (16,000) and minimum tape wavelength, heat transfer was enhanced by 21%, while the pressure drop was augmented by 1.4 times. Investigation of the thermo-fluidic performance of the nanofluid revealed that for flows inside tubes with elliptical shape, the use of nanofluid is more desirable than pure water, and nanofluid is recommended when there is a twisted tape in the flow path. Streamlines at Reynolds number of 16,000 inside elliptical shape for λ2-3 = 0.1–0.2 m with variable wavelength