Abstract
An investigation is presented of free convection in horizontal concentric annuli of varying with inner shape where the inner and outer surfaces are kept at a constant temperature. The simulation is categorized into four groups based on the shape of the inner entity, which is either cylindrical, elliptical, square, or triangular. Flow and thermal fields are exhibited by means of streamlines and isotherms. Overall heat transfer correlations incorporating thermal radiation are established and presented in terms of the Nusselt number. It is observed that the surface radiation and presence of corners and larger top space enhances the heat transfer rate. As the reference temperature increases, surface radiation plays a more prominent role in the overall heat transfer performance.