This research uesd to compute the flow field variables of natural convection air flow based on
finite difference computational fluid dynamic methods. The problem considered deals with a twodimensional
internal, laminer , isothermal flow over a vertical rectangular duct. In this work,
governing equations were solved using finite different forward explicit technique. The flow
characterstics are evaluated for Prandtl number at 0.7 and dimensionless inlet velocity equals to
0.005. The results explain that the heat transfer rate is a strong function of flow velocity also the
hydrodynamic properties such as pressure, temperature and velocity are increased when the flow
moves upward the duct.The results showed a good agreement with other published results.