Flow and heat transfer characteristics of nanofluids containing rod-like particles in a turbulent pipe flow

Numerical simulations of water-based ZnO nanofluids containing rod-like nanoparticles in a turbulent pipe flow are performed by solving the modified equations of Reynolds averaged Navier-Stokes, turbulence kinetic energy and turbulence dissipation rate with rod-like nanoparticle term, the general dynamic equation for rod-like nanoparticles and the equation describing the probability density functions for the rod-like nanoparticle orientation. Some results are validated by comparing with the available experimental or numerical results. The results show that the friction factor of nanofluids, being larger than that of the pure water, decreases with increasing Reynolds number and particle aspect ratio, and decreases when particle volume concentration Φ is changed from 0.4 v% to 0.93 v% and then increases when Φ is changed from 0.93 v% to 1.3 v%. The heat transfer of nanofluids is higher than that of the pure water. The ratios of Nusselt number for the nanofluid and pure water increase with increasing Reynolds number, particle aspect ratio and volume concentration. The ratios of energy performance evaluation criterion (PEC) for the nanofluids and pure water, PECnf/PECf, are less and larger than unity when Re < 10,000 and Re > 10,000, respectively. The values of PECnf/PECf increase with increasing the particle aspect ratio, and are not monotonously dependent on the particle volume concentration. It is more effective to use nanofluids containing rod-like nanoparticles with larger aspect ratio, at higher Reynolds number and at a suitable particle volume concentration. Finally the expressions of PECnf/PECf as a function of Reynolds number, particle volume concentration and particle aspect ratio are derived based on the numerical data.