2. Natural Convective Heat Transfer from Horizontal Isothermal Circular, Square, Two-Dimensional, and Rectangular Shaped Surfaces

In this chapter, consideration is given to natural convective heat transfer from horizontal heated plane surfaces of relatively simple shape that are imbedded in a surrounding adiabatic surface, the heated and adiabatic surfaces being in the same horizontal plane. Attention is limited to surfaces that have a uniform surface temperature, i.e., which are isothermal, and to cases where, if there is a heated surface, it is facing upward and if there is a cooled surface, it is facing downward. Natural convective heat transfer from heated surfaces having circular, square, and rectangular shapes is considered. In addition, consideration is also given to the natural convective heat transfer from a plane two-dimensional surface. The results for the rectangular surface for the various aspect ratio values considered have been expressed in terms of Nusselt and Rayleigh numbers based on the characteristic length and the variations obtained for all aspect ratios considered are shown to be effectively the same in the laminar and fully turbulent flow regions.