Natural convection heat transfer from a vertical, 3.02 m high by 2.95 m long, electrically heat surface in air was studied. The air was at the ambient temperature and the atmospheric pressure, and the surface temperature was varied from 60 C to 520 C. These conditions resulted in Grashof numbers up to 2 × 1012 and surface-to-ambient temperature ratios up to 2.7. Convective heat transfer coefficients were measured at 105 locations on the surface by an energy balance. Boundary layer mean temperature profiles were measured with a thermocouple. Results show that: (1) the turbulent natural convection heat transfer data are correlated by the expression  
Nuy=0.098Gry1/3TwT0.14
when all properties are evaluated at T; (2) variable properties do not have a significant effect on laminar natural convection heat transfer; (3) the transition Grashof number decreases with increasing temperature; and (4) the boundary layer mean temperaturue profiles for turbulent natural convection can be represented by a “universal” temperature profile.
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