The present work details a numerical simulation of forced convective laminar flow in a channel with a heated obstacle attached to one wall. The second law analysis is employed to investigate the distribution of entropy generation in the flow domain to demonstrate the rate of irreversibilities in thermal system. The conjugate problem including the convection heat transfer in the fluid flow and conduction one inside the obstacle is solved numerically to obtain the velocity and temperature fields in both gas and solid phases. To reach this goal, the set of governing equations including momentum and energy equations for the gas phase and conduction equation for the obstacle are solved by CFD technique to determine the hydrodynamic and thermal behaviors of the fluid flow around the obstacle and the temperature distribution in the solid element. An attempt is made to detail the local Nusselt number distribution and mean Nusselt number and also the local entropy generation distribution for the individual exposed obstacle faces. A good consistency is found between the present numerical results with experiment.