Abstract Measurements were carried out to investigate the enhancement in the heat transfer and the influence of the flow friction in a rectangular channel using periodic zigzag (multiple V-shaped) ribs affixed, in tandem, on the bottom surface of the channel, which was heated with a uniform heat flux. A horizontal rectangular channel with an aspect ratio, (height/width), of 1:4 was examined. The ribs were arranged in an in-line arrangement such that repeated V-shaped secondary flow cells were established. The present experiments were conducted for a range of Reynolds number from 15,000 to 75,000, rib height-to-pitch (e/p) ratio between 0.0375 and 0.15, and for three rib angles (α) of 30, 45 and 60 deg, respectively. An efficiency index of about 0.6 was observed for rib angles of 45 and 60 deg. at the lowest rib height to pitch ratio. New correlations were obtained for the influence of rib height-to-pitch ratio, rib angle, and Reynolds number on both Nusselt number enhancement ratio and flow friction factor ratio.