Experimental study of natural convection in a horizontal cylinder with different end temperatures

The phenomenon of natural convection in a horizontal pipe with different end temperature was studied experimentally in a cylindrical cavity with the ratio (diameter) (length) = 0.112 . The Rayleigh number based on diameter was in the range 108 < Ra < 1010. It was concluded that in this range the natural convection mechanism departs considerably from the pattern known in the limit Ra → 0. Specifically, the end-to-end heat transfer is effected via two thin horizontal jets, the upper (warm) jet proceeding along the top of the cylinder toward the cold end and the lower (cold) jet advancing along the bottom in the opposite direction. The region sandwiched between the two jets is filled with nearly stagnant fluid. In this region the temperature varies linearly with depth. In each vertical cross-section, the top-bottom temperature difference is of the same order of magnitude as the end-to-end temperature difference. The Nusselt number for end-to-end heat transfer was shown to vary weakly with the Rayleigh number.