The process of combined turbulent natural convection and radiation in a bottom-heated, horizontal layer of an optically thick fluid medium, confined between two rigid, parallel, and conducting plates at high temperatures, is studied analytically based upon a simple eddy diffusivity model. The model is developed by a phenomenological approach with special emphasis on the mean temperature structure in the intermediate wall region. It is demonstrated that, when radiation is present in the layer in addition to convection, the temperature field ceases to be symmetric with respect to the center plane. In particular, the upper and the lower thermal boundary layers are shown to be quite different in thickness while the turbulent core temperature is shown to deviate significantly from the value for purely turbulent convection. Calculation of the radiation-enhanced heat flux is made and is found to be in good qualitative agreement with those obtained in related studies.
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