3. Natural Convective Heat Transfer from Upward Facing Horizontal Plane Surfaces of Complex Shape

Natural convective heat transfer rates from horizontal heated isothermal surfaces of more complex shape are considered in this chapter. The surfaces considered are imbedded in a surrounding plane horizontal adiabatic surface, the heated and adiabatic surfaces being in the same horizontal plane. The surface shapes considered are (a) a circular heated surface with an adiabatic inner circular section, (b) a square-heated surface with an adiabatic inner square section, (c) a square-heated surface with an adiabatic inner rectangular section, (d) an I-shaped heated surface, and (e) a +-shaped (plus-shaped) heated surface. The results for these surface shapes show that if the variations of Nusselt number with Rayleigh number for the various shapes are expressed in terms of Nusselt numbers and Rayleigh numbers based on the characteristic length, then the variations of Nusselt number and Rayleigh number for all the surface shapes are essentially the same in the laminar and the fully turbulent flow regions.