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

In the present work, CFD study was performed for a computational domain of a 3 x 3 square array of vertical heat generating cylinders with a pitch to diameter ratio (P/D) equal to 2. The assembly was enclosed in a 127 mm diameter pipe. Each rod had a diameter of 12.7 mm and a heating length of 570 mm. The fluid entered and left the computational domain radially. Constant heat flux boundary conditions were employed for different heat flux values. Due to the radial entrance of fluid, swirls are formed at both inlet and outlet which resulted in turbulence. K-Omega model was used to include the effects of turbulence. Surface temperature for different positions of several cylinders was calculated and compared with experimental results. A good agreement was found between experimental data and computational results. The heat transfer coefficient, modified Rayleigh number and Nusselt number can also be calculated. After developing the method, temperature and velocity profile for different values of heat flux, heating rods arrangements and dimensions of the assembly can be predicted for design purposes. Correlations based on simulations results can be proposed for natural convection calculations in assembly of vertical heating rods.