Numerical simulation of convective heat transfer of non-Newtonian carbon-based nanofluids in U-bend tubes using Buongiorno’s model

Abstract

The laminar forced convective heat transfer of multi-walled carbon nanotubes (MWCNTs)/water nanofluids with shear-thinning rheological behavior inside curved tubes is addressed in the present study. The four-equation model was selected to model the fluid flow and heat transfer of the nanofluid accounting for the Brownian diffusion and thermophoresis forces, and the viscosity variation of the carbon-based nanofluid was approximated by the well-known power-law viscosity function. The governing equations were discretized using the finite volume method and solved in the OpenFOAM CFD package. The developed CFD code was validated against proper experimental data. A comprehensive parametric study was carried out to investigate the effect of pertinent parameters on the problem, including Reynolds and Dean numbers, bend radius and the concentration of the carbon nanotubes. It is shown that even for low Reynolds numbers, thermal performance factors up to 1.27 can be obtained in curved pipes using carbon-based nanofluids. Moreover, MWCNT/water nanofluids demonstrate superior thermal performance in comparison with metal oxide nanofluids inside curved flow passages (e.g., 14% heat transfer enhancement at Re = 900). Finally, an accurate numerical correlation is presented for the non-Newtonian nanofluid forced convective heat transfer inside curved tubes.