An experimental investigation on turbulent natural convection boundary layers has been conducted with water on a vertical plate of constant heat flux. Local heat transfer data are presented for laminar, transition, and turbulent natural convection, with the emphasis on the turbulent regime. The data extend to a modified Rayleigh number of 1016 for a threefold range in Prandtl number. The results indicate that natural transition occurs in the range 1012 < Ra* < 1014; i.e., fully developed turbulent flow occurs by Ra* = 104. This latter value can be as low as 2 × 1013 with the use of a trip rod. The physical structure of the turbulent boundary-layer flow was studied using the combined time-streak marker hydrogen bubble method. Temperature data and temperature corrected velocity data obtained by hot-film sensors are presented for Ra* values between 8.7 × 1013 and 7.1 × 1014. For the range of variables investigated, the major conclusions are (a) the local heat transfer coefficient exhibits a slight decrease with length, (b) confirmation that the vortex street layer in the transition region decays into a longitudinal-vortex-type structure, and (c) the outer portion of the thermal and velocity fields can be approximated by power profiles that fit almost all the data available to date.

The emission of thermal radiation from a microscopically roughened dielectric surface is treated using a laminar-inhomogeneous layered model for a representation of the effective spatial variation in refractive index associated with a roughened surface layer. The Riccati equation is used to calculate the modification to the spectral angular transmittance of the surface due to the presence of this inhomogeneous surface layer. A consideration of the emission of radiant energy from the bulk dielectric through the surface layer permits the angular emittance to be determined. Total emittance values are obtained using the spectral angular emittance data.

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