Investigating the mixed convection heat transfer of a nanofluid in a square chamber with a rotating blade

Mixed convection heat transfer of water-alumina nanofluid in a square chamber with a rotating blade in its center is studied numerically. The governing equations are discretized by using a finite-difference method and solved simultaneously using the SIMPLE algorithm. The blade thickness is assumed to be negligible, the vertical walls of the chamber are at constant temperature of Tc and Th, and the horizontal walls are insulated. The effects of Rayleigh number (10(3) <= Ra <= 10(6)) and Richardson (0.1 <= Ri <= 100) number, the dimensionless length of the blade (0.6 <= a <= 0.8) and the volumetric percentage of nanoparticles (0 <= phi <= 0.03) on flow and thermal fields are investigated. The results show that an increase in Rayleigh number, volumetric percentage of nanofluid and blade length leads to heat transfer increasing in most cases, but an increase in Richardson number results in a reduction in heat transfer. It is revealed that the maximum blade rotation occurs at small Richardson numbers.