Advanced passive heat transfer enhancement: numerical analysis of TiO₂-water nanofluid flow

The primary objective of this study is to investigate the heat transfer enhancement, friction factor, and thermal performance factor of a plain tube with single and double twisted tapes, combined with a semicircular cut with and without dimples, a perforated V-cut, and conical rings, using a TiO2-water nanofluid. Numerical simulations of tube flow and heat transfer were conducted. The nanofluid used in the simulations contains TiO₂ nanoparticles at concentrations of 0.5% and 1.5% by volume. The nanofluid inlet temperature was set at 300 K, and boundary conditions were applied. The maximum heat transfer coefficient increases from plain tube to 88.2% and 71.42% at double twisted tape with perforated V-cut and semi-circular cut, respectively, with dimples in 0.5% and 1.5% TiO₂ concentrations. The maximum Nusselt number increased by 115.53% and 100.9% at double twisted tape with perforated v-cut and semi-circular cut with dimples compared to the plain tube in 0.5% and 1.5% TiO₂ concentrations, respectively. The simple tube with a perforated V-cut and a conical ring insert exhibits a 94.44% higher friction factor at a 1.5% TiO₂ concentration. The maximum thermal performance factor was found to be 2.04 for double twisted tapes at a 0.5% TiO₂ concentration. Additionally, this study presents contour plots of the velocity distribution, pressure distribution, temperature distribution, and turbulent kinetic energy.