Numerical study of natural-convection from horizontal cylinder at eccentric positions with change in aspect ratio of a cooled square enclosure

This numerical study reports the change in natural-convection heat transfer characteristics from a stationary 2D horizontal cylinder with the change in the aspect ratio (ratio of cylinder radius to enclosure length, R/L) of a cooled square outer enclosure and position of the cylinder for Rayleigh number (Ra-D) of 1.114 x 10(4) and 1.114 x 10(5). The cylinder position is varied between concentric to eccentric positions along the horizontal and vertical median and diagonal of the enclosure for R/L in the range from 0.1 to 0.225. The simulations are performed under non-Boussinesq conditions and Immersed Boundary Method to model the cylinder surface. The combination of thermal stratification effects, optimized convection flow and the effect of heat conduction between cylinder periphery and the enclosure wall is found to determine the net heat transfer behavior. For eccentricity along the vertical median of the enclosure, the position near the bottom wall and the position near the top wall results in heat transfer enhancement at the lower R/L values and higher R/L values respectively. The concentric position of the cylinder results in maximum heat transfer at R/L = 0.15 for Ra-D =1.114 x 10(4) and at R/L = 0.175 for Ra-D = 1.114 x 10(5). For eccentricity along the diagonal, the position near the top wall results in maximum heat transfer enhancement at R/L = 0.175 and higher for Ra-D = 1.114 x 10(4) and at R/L = 0.2 and higher for Ra-D = 1.114 x 10(5). The intensity of the chimney effect depending on the Rayleigh number is found to be the driving parameter at lower R/L values which determines the optimum cylinder position along the horizontal median. The effect of heat conduction with the vertical wall results in heat transfer enhancement for the position nearest to the vertical wall at R/L values higher than 0.175.