A numerical and experimental study is performed to analyze the steady-state turbulent flow and heat transfer for spatially periodic flows past an array of ribs aligned along the channel axis. The data includes mean velocities profiles, turbulence intensities, friction loss, and heat transfer characteristics. The effects of rib height-to-channel height ratio, rib pitch-to-rib height ratio, and flow Reynolds number are examined. The rib height-to-channel height ratios are 0.12, 0.18, and 0.24; the rib pitch-to-rib height ratios are 10, 15, and 20; and the Reynolds number is varied from 15000 to 50000. The time-averaged conservation equations of mass, momentum, and energy are solved together using a finite analytic numerical solution using a nonlinear k model. The computed data are shown to be in satisfactory agreement with the experimental data. The results indicate that both friction factor and heat transfer coefficient values for ribbed ducts increasing with increasing in the value of rib height-to-channel height ratio and with decreasing in the value of the rib pitch-to-rib height. In addition, the results show that the average Nusselt number enhancement ratios for the channel flows with ribs aligned along channel axis are lower than those of the attached rib case of Hwang and Liou (1994). Also, new empirical correlations for average Nusselt number enhancement ratio and friction factor ratio are obtained in terms of rib and flow parameters. The thermal performance at a constant pumping power improvement as high as 13% relative to a smooth channel, can be achieved at lower Reynolds number.