Several numerical and experimental studies of natural convective heat transfer from two-sided heated horizontal plates are available. In the numerical studies it has usually been assumed that the plate is thin, effectively having no thickness, whereas plates of finite thickness have been used in the experimental studies. The main aim of the present study is to determine whether the plate thickness has a significant influence on the heat transfer rates from the plate surfaces. The effect of the vertical side surface thermal boundary condition and the effect of the plate shape on the heat transfer rates have been also studied. Heat transfer results have, therefore, been numerically obtained for circular and square plates having various thicknesses. The upper and lower plate surfaces have been assumed to be isothermal and at the same temperature. Both the cases where the vertical side surface of the plate is isothermal and at the same temperature as the upper and lower plate surfaces and the case where this vertical side surface is adiabatic have been considered. The solution has been obtained using ANSYS FLUENT©. Variations of the mean Nusselt number with Rayleigh number for various dimensionless plate thicknesses for the two vertical side surface conditions have been obtained for both plates. To validate the numerical results, a limited range of experiments has been undertaken for both shapes. Mean heat transfer rates have been obtained using the lumped capacity method. Results have only been obtained for the case where the plates are exposed to air.
