Experimental study of natural convection heat transfer from an enclosed assembly of thin vertical cylinders

Steady state heat transfer by natural convection was investigated experimentally from an enclosed assembly of thin vertical cylinders at high Rayleigh numbers. The published literature lacks any information regarding such a study in the turbulent boundary layer regime. All the available literature is for the laminar region for an enclosed assembly. The enclosed assembly consisted of a 3 × 3 array of vertical cylinders immersed in a large volume tank of water. All the cylinders were electrically heated. Uniform heat fluxes at various power levels were applied to each cylinder and the surface temperature at different positions along the cylinders were recorded. The experimental results show that the surface temperature distribution increases axially up to a certain length, then decreases due to mixing which increases the heat transfer. The heat transfer coefficient, Nusselt number and modified Rayleigh number have also been presented for the experimental data. Empirical correlations between overall Nusselt number and average modified Rayleigh number have been developed for an assembly of cylinders. This empirical correlation for an assembly is valid for 1.28 × 1012 ≤ RaL∗¯≤ 1.18 × 1013. The maximum natural convection at central cylinder and Chimney effects in an assembly are observed during these experiments.

Research Highlights
► The empirical correlations for an assembly is valid for 1.28 × 1012 ≤ RaL∗¯≤ 1.18 × 1013.
► Temperature increases axially up to a certain length of cylinder, then decreases due to mixing.
► Overall Nusselt number for the assembly of vertical cylinders is about 30% higher than single cylinder.
► Ratio of Nusselt number for assembly to single cylinder is well above unity.