A numerical study was undertaken for investigating the heat transfer enhancement in a tube with triangular cross sectioned ribs. The spacing between the ribs were kept constant as a distance of tube diameter, D. Three different rib thicknesses were considered for numerical analyses. Uniform heat flux was applied to the external surface of the tube and air was selected as working fluid. Numerical calculations were performed with FLUENT 6.1.22 code, in the range of Reynolds number 8000-36000. The results obtained from a smooth tube and rib inserted tube were compared with those from the experimental studies in literature in order to validate the numerical method. The variation of Nusselt number, friction factor and overall enhancement ratios for the tube with triangular cross sectioned ribs were presented. Consequently, a maximum gain of 1.34 on overall enhancement ratio is obtained for S/D = 0.75.