Flow and heat transfer are simulated numerically in a 3-dimensional square duct supplied with circular turbulators for different values of the turbulator height to the duct height (Blocking ratio BR). The investigated blocking ratios of these circular obstacles are 0.1, 0.15 and 0.2. Reynolds number for all cases is fixed at 5477. Top and bottom faces of the duct in the test region are subjected to 200 W/m2 heat flux. Turbulators number effect is examined in a range of (1-2-5-7). The fixing angle is taken of range (0, 30, and 45). The influence of these parameters on both heat transfer and fluid flow are examined. Ansys-Fluent 18 is implemented to perform the numerical simulation. The simulation of fluid flow is performed using realizable k-ε turbulence model. It was found that the presence of these turbulators has a significant effect on the heat transfer. Further that the heat transfer rate directly proportional to the blocking ratio, number of turbulators, and fixing angle. In general, the enhancement ratio of heat transfer could reach 30%.