Numerical investigation of natural convection of Al2O3 nanofluid in vertical annuli

This paper presents the numerical study of internal free convection of Al2O3 water nanofluid in vertical annuli. Vertical walls are maintained at constant temperatures and horizontal walls are adiabatic. Results are validated by experimental data. Effect of nanofluids on natural convection is investigated as a function of geometrical and physical parameters and particle fractions for aspect ratio of 1 a parts per thousand currency sign H/L a parts per thousand currency sign 5, Grashof number of 10(3) a parts per thousand currency sign Gr a parts per thousand currency sign 10(5) and concentration of 0 a parts per thousand currency sign I center dot a parts per thousand currency sign 0.06. More than 330 different numerical cases are investigated to develop a new correlation for the Nusselt number. This correlation is presented as a function of Nusselt number of base fluid and particle fraction which is a linear decreasing function of particle fraction. The developed correlation for annuli is also valid for the natural convection of Al2O3 water nanofluid in a square cavity. Furthermore, the effect of the viscosity and conductivity models on the Nusselt number of nanofluids in cylindrical cavities are discussed.