Interaction effects between surface radiation and turbulent natural convection in square and rectangular enclosures

The interaction effects of surface radiation with turbulent natural convect ion of a transparent medium in rectangular enclosures have been numerically analyzed,covering a wide range of Rayleigh number from 10(9) to 10(12) and aspect ratio from 1 to 200. The vertical walls of the enclosure are isothe rmal and maintained at different temperatures. The adiabatic top and bottom walls of the enclosure have been modelled for the limiting cases of neglig ible or perfect conduction along their lengths. The interaction with surfac e radiation results in larger velocity magnitudes and turbulence levels in the vertical as well as horizontal boundary layers, leading to an increase in the convective heat transfer ky similar to 25 percent. Due to the asymme trical coupling of radiation, the augmentation of convective Nusselt number of the cold wall is larger than that of the hot wall. In tall enclosures, the convective Nusselt number exhibits three distinct regimes with respect to aspect ratio, viz. the slow growth regime, the accelerated growth regime and the invariant (or saturated) regime. The augmentation of convective Nu sselt number for perfectly conducting horizontal walls is found to be of si milar nature to that in the case with radiation interaction.