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 threedimensional 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 (lambda and gamma) 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 lambda or gamma Also, for a given Ri(1) or Ri(o), the inner and outer wall convective heat transfer coefficient does not increase permanently with increase in lambda or gamma