Richardson Number Ratio Effect on Laminar Mixed Convection of a Nanofluid Flow in an Annulus

The effect of Richardson number ratio of the walls on the laminar mixed convection of a nanofluid flowing in an annulus which was heated uniformly is studied numerically. The finite volume technique is utilized to discretize and to solve a set of three-dimensional elliptic governing equations. The secondary flows and contour of the dimensionless axial velocity and dimensionless temperature are presented and discussed. For a given inner or outer wall Ri, the convective heat transfer coefficient of the walls changes differently with Richardson number ratio ( and γ) while inner, outer, and area average friction coefficients do not significantly change. The dimensionless axial velocity profiles shift toward the wall whose Richardson number has a fixed value at the upper vertical plane. The most effect on the axial velocity occurs at the upper vertical plane with respect to or γ. Also, for a given Rii or Rio, the inner and outer wall convective heat transfer coefficient does not increase permanently with increase in or γ.