Experimental invesitgation of free convection on a vertical rod bundle.

Free convection in a vertical, enclosed rod bundle was experimentally investigated for a wide range of Rayleigh numbers. A uniform power dissipation per unit length is supplied to each rod, and the enclosing outer cylinder is maintained at constant temperature. Nusselt number for each rod, as well as an overall value for the bundle have been obtained as a function of Rayleigh number. Comparison of the results for air and water indicate that, for a fixed Rayleigh number, an increase in the Prandtl number produces a reduction in the Nusselt number. This is contrary to what has been reported for vertical cavities, and is attributed to curvature effects. Furthermore, the data reveals the interesting fact that it is quite possible for the individual rods in the array, at a given Rayleigh number, to exchange energy with the working fluid via different but coexisting flow regimes. This is especially evident at the end of the conduction regime for the rod bundle as a whole. (A)