In this model, a numerical study of two dimensional steady natural convection is performed for a uniform
heat source applied on the inner circular cylinder in a square air (Pr=0.7) filled enclosure in which all
boundaries are assumed to be isothermal (at a constant low temperature). The developed mathematical
model is governed by the coupled equations of continuity, momentum and energy and is solved by finite
volume method. The effects of vertical cylinder locations and Rayleigh numbers on fluid flow and heat
transfer performance are investigated. Rayleigh number is varied from 103 to 106 and the location of the
inner cylinder is changed vertically along the centerline of the enclosure from ?0.25 L to 0.25 L upward and
downward, respectively. It is found that at small Rayleigh numbers does not have much influence on the flow
field while at high Rayleigh numbers have considerable effect on the flow pattern. In addition, the numerical
solutions yield a two cellular flow field between the inner cylinder and the enclosure. Also, the total average
Nusselt number behaves nonlinearly as a function of locations. Results are presented in terms of the
streamlines, isotherms, local and average Nusselt numbers. Detailed results of the numerical has been
compared with literature ones, and it gives a reliable agreement.