An interferometric investigation of the effect of separation distance and temperature imbalance on natural convection for two horizontal cylinders at moderate Rayleigh numbers

An experimental investigation has been carried out to study the natural convection interaction between a pair of horizontal cylinders located directly one above the other. It is found that the presence of the upper cylinder has negligible effect on the heat transfer rate from the lower cylinder, thus attention has been given on the heat transfer characteristics from the upper cylinder The ratio S/D of the center-to-center separation distance was varied from three to six by a step of one. The temperature imbalance ΔT₁/ΔT₂ was also varied independently. The experiments were conducted with Rayleigh numbers varying from 6300 to 13000. It was found that maximum enhancement of the heat transfer from the upper cylinder for a given ratio S/D depends primarily from the temperature imbalance ΔT₁/ΔT₂ and weakly from the Rayleigh number. The experimental results for the maximum enhancement, can be presented fairly well by the empirical formula (ΔT₁/ΔT₂)_op=0.136(S/D)^0.75 for 2≦S/D≦6, 1000≦Ra≦200000. The findings of this investigation agree closely with those previously reported in the literature.