In the current study, the numerical analysis of the turbulent flow field and heat transfer in a flat rectangular channel having roughness elements on its bottom surface is conducted. Two dimensional, steady, incompressible and turbulent flow simulations are carried out using the Finite Volume Method (FVM). In this regard, the structured non-uniform quadrilateral mesh is chosen, where the pressure term is discretized using the standard scheme while all other governing equations are discretized by using second order upwind scheme. The SIMPLE scheme is used for coupling the pressure velocity field. The effect of important parameters such as Reynolds number (5400 < Re < 23000), ratio of roughness height to channel height (0.06 < e/H < 0.26) and ratio of roughness thickness to pitch (0.25 < t/P < 1.0) on average Nusselt number, friction factor and thermal performance improvement factor has been investigated. It is found that increase in Reynolds number increases the heat transfer rate but decreases the thermal performance factor. Moreover, increase in ratio of thickness to pitch and decrease in ratio of height to channel improves the thermal performance. The RNG k ε turbulence model shows better prediction compared to the experimental data.