Enhancing the thermal performance of a micro finned tube with TiO₂–water nanofluids using twisted tape inserts

This paper investigates the heat transfer characteristics and friction factor of finned microtube fitted with twisted tape inserts. Results show that the performance of the finned microtube with nanofluid depends on concentration of nanoparticles, pitch ratio, and the type of the pitch used. With increase in the concentration of nanoparticle with the base fluid the viscosity of the nanofluid increased by 30% compared to the fluid with concentration of 0.05%. The increase in the concentration of nanoparticles leads to increased pressure drop and pumping power. For the Reynolds number Re = 2000, the maximum performance ratio is found to be 1.5, 2.05, 2.1, and 2 for 0, 0.05, 0.1, and 0.2% concentration ratio, respectively. Similarly, with increase in the Reynolds number from 2000 to 10,000 the performance ratio decreases. Moreover, the results of performance ratio revealed that the use of a nanofluid have performance more than unity. Similarly, the performance of finned microtube heat exchanger is higher in the case of twist ratio (LR-Y = 6) and concentration ratio (φ = 0.2%), as the turbulence inside the tube is greatly influenced by the boundary layer separation by the inserts for enhanced friction ratio (f/f_p) and Nusselt number ratio (Nu/Nu_p) compared to a smooth plain tube.