Enhancement of natural convection heat transfer from a horizontal cylinder due to vertical shrouding surfaces

A comprehensive experimental study has been performed to determine the natural convection heat transfer characteristics of a heated horizontal cylinder situated in a vertical channel in air. Fifteen different channel configurations were employed, encompassing a wide range of channel heights and of spacings between the channel walls. Shroud walls having various thermal characteristics (highly conducting, highly conducting/rear insulated, and insulating) were used to form the channel. For each configuration, the cylinder Rayleigh number ranged from 1.5 × 10⁴ to 2 × 10⁵. It was found that a cylinder situated in a channel experiences enhanced natural convection heat transfer compared with a cylinder situated in unbounded space. Enhancements of up to 40 percent were encountered for the parameter ranges of the experiments. The enhancement is accentuated as the interwall spacing is decreased and as the channel height is increased. There is no enhancement for interwall spacings of 10 diameters or more. It was also found that the Nusselt number was quite insensitive to the various types of shroud walls employed. Measured temperature distributions along the shroud walls displayed different degrees of uniformity depending on whether the wall was conducting or insulating.