A thermal hydraulic study of convective heat transfer in 3 3 square array of heated vertical cylinders is carried out using computational fluid dynamics (CFD). Two different CFD approaches were used, i.e., full structural details (FSD) and porous media modeling (PMM). The computational requirement in PMM declined significantly due the porous media approximation. The PMM only gives the overall flow and temperature field. In the FSD model all the geometry details are presented without any approximation. The PMM and FSD results are compared to experimental data. In general, the prediction of temperature profiles from both PMM and FSD agreed well with the experimental data.