Thermal performance and pressure drop analysis of nanofluids in turbulent forced convective flows

Abstract

In this research the enhancement of nanofluids convective heat transfer through a circular tube with a constant heat flux condition in the turbulent flow regime is numerically studied. All of the nanofluid properties depend on temperature and nanoparticle volume concentration. The incompressible and steady-state forms of continuity, Navier–Stokes and energy equations have been solved using finite volume approach with the SIMPLER algorithm. In order to demonstrate the validity and precision of the numerical procedure, calculated friction factors and Nusselt numbers have been compared with the experimental data and the well-known correlations. To attain the best prediction, the different turbulence models are examined and it has been observed that the best model to predict the near wall treatment is based on enhanced wall function in the κ–ɛ turbulence model. The effects of nanoparticle concentration (1–10% Al2O3) in EG/water mixture, Reynolds and Prandtl numbers on the heat transfer rate have been investigated. A dimensionless effectiveness quantity has been defined to measure the thermal performance of nanofluid in comparison with the base fluid with the same Reynolds number. But for a fixed pumping power, due to more increase of viscosity, the nanofluids heat transfer coefficient has been decreased by adding nanoparticle concentration. From the results, it can be deduced that for a fixed Reynolds number, increasing the particle concentration enhances convective heat transfer rate considerably. Moreover, there is a large pressure drop and pumping power when using nanofluids instead of base fluid with the same Reynolds number. Thus using nanofluids may be not a good candidate for the practical applications in turbulence region, in which an increase in pumping power is an important problem.