Abstract
This numerical study investigates the steady state natural convection of light and heavy water entering a vessel from the left and leaving on the right. The cavity consists of a matrix of cylindrical heated rods as in light and heavy water reactors. The aim of the study is to describe the effects of water inlet velocity on the flow and thermal fields in presence of such heated obstacle. The investigations are conducted for different values of rods temperatures. From the numerical results, it is evident that the flow pattern and temperature fields are significantly dependent on the water inlet velocity and rods temperature