Experimental, Variable Properties Natural Convection From a Large, Vertical, Flat Surface

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 60C to 520 C. These conditions resulted in Grashof numbers up to 2 x 10/sup 12/ 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 a a Nu/sub y/ = 0.098Gr/sub y//sup 1/3/(T/sub w//T/sub infinity/)/sup -0.14/ =(when all properties are evaluated at =(T-italic/sub infinity/; (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 temperature profiles for turbulent natural convection can be represented by a ''universal'' temperature profile.