The effect of surface shape on laminar natural convective heat transfer from vertical isothermal hexagonal and octagonal flat plates embedded in a plane adiabatic surface, the adiabatic surface being in the same plane as the surface of the heated plate, has been numerically investigated. Results for the hexagonal and octagonal surface shapes with different aspect ratios have been obtained. It has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces, this having been treated using the Boussinesq approach. The solution has been obtained by numerically solving the full threedimensional form of governing equations, these equations being written in dimensionless form. The solution was obtained using the commercial finite volume method based cfd code, FLUENT C⃝ 14.5. The solution has the surface shape, the Rayleigh number, the dimensionless plate width and the Prandtl number as parameters. Results have only been obtained for a Prandtl number of 0.7 for Rayleigh numbers between 10 3 and 10 8 for various surface shapes with width-to-height ratios between 0 and 0.6. The effect of these parameters on the mean Nusselt number has been studied and empirical correlation equations for the mean heat transfer rate have been derived. C⃝ 2016 Wiley Periodicals, Inc. Heat Trans Asian Res, 00(0): 1-22, 2016; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj).

Natural convective heat transfer from the exposed top surface of an inclined isothermal cylinder, with a circular cross-section, mounted on a flat adiabatic base plate has been numerically investigated. The cylinder is mounted normal to the flat adiabatic base plate. The numerical solution has been obtained by solving the dimensionless governing equations, subject to boundary conditions, using the commercial finite volume method based code FLUENT. The flow has been assumed to be symmetrical about the vertical center-plane through the cylinder. Results have only been obtained for Prandtl number of 0.7, this being the value existing in the application that originally motivated this study. The simulations consider Rayleigh numbers between 10 3 and 10 7 , inclination angles between 0 o and 180 o , and dimensionless cylinder diameters between 0.25 and 1.The effects of dimensionless diameter, Rayleigh numbers, and inclination angles on the mean Nusselt number for the top exposed surface of the cylinder have been studied.Empirical correlations for the heat transfer rates from the top exposed surface of the cylinder have been derived.