Numerical validation of experimental heat transfer coefficient with SiO2 nanofluid flowing in a tube with twisted tape inserts

• Experiments are undertaken with SiO2 nanofluid up to 4% volume concentration.
• Numerical model is developed for nanofluid flow with twisted tape insert for a wide range of Reynolds number.
• SiO2 nanofluid gives maximum heat transfer coefficient of 94.1% at 3.0% concentration at a twist ratio 5.
• Coefficient of eddy diffusivity and Prandtl index is obtained as a function of Re, concentration and twist ratio.
• Numerical results are in good agreement with exp data with SiO2, Al2O3 and Fe3O4 nanofluids.

A numerical model has been developed for turbulent flow of nanofluids in a tube with twisted tape inserts. The model is based on the assumption that van Driest eddy diffusivity equation can be applied by considering the coefficient and the Prandtl index in momentum and heat respectively as a variable. The results from the numerical analysis are compared with experiments undertaken with SiO2/water nanofluid for a wide range of Reynolds number, Re. Generalized equation for the estimation of nanofluid friction factor and Nusselt number is proposed with the experimental data for twisted tapes. The coefficient and the Prandtl index in the eddy diffusivity equation of momentum and heat is obtained from the numerical values as a function of Reynolds number, concentration and twist ratio. An enhancement of 94.1% in heat transfer coefficient and 160% higher friction factor at Re = 19,046 is observed at a twist ratio of five with 3.0% volumetric concentration when compared to flow of water in a tube. A good agreement with the limited experimental data of other investigators is observed with Al2O3 and Fe3O4 nanofluids indicating the validity of the numerical model for use with twisted tape inserts.