Nanofluids forced convection heat transfer inside circular tubes

摘要

Two-dimensional turbulent convective heat transfer behaviour of alumina (Al_2O_3) nanoparticle dispersion in water flow in a horizontal circular pipe at constant wall temperature is investigated numerically. The computational procedure is based on the finite-volume technique. Three stream velocities corresponding to 5,000 < Re < 4 × 10~6 and five different concentrations of nanoparticle (0%, 1%, 2%, 4% and 6%) are studied. The full range of flow at the entrance length and the fully developed are considered. The shear stress are observed to increase at any x station along the pipe as the concentration of nanoparticle increase and it attains its higher value at the beginning of the pipe at the entrance region and then drops to an asymptotic value at the fully developed region. However, the case is reversed for Nusselt numbers along the pipe wall where they decrease as the concentration increase at each specific velocity value and in general as the velocity increases both Nusselt number and the shear stress increase. Different envelopes are obtained for Nusselt numbers and the shear stress in terms of Reynolds number. Finally, Reynolds number is observed to decrease as the concentration increase at fixed inlet velocity.