The effect of the rib-angle orientation on heat transfer distribution was experimentally studied inside twopass variable cross-section channels.The heat transfer distributions for ribbed channels were compared with channels without ribs.Ribs with rectangular crosssection were arranged symmetrically on two opposite walls.Analysis of the experimental results may lead to the following conclusions:the heat transfer effect of the channel with ribs is 50% higher than that of the channel without ribs.The 60° ribs were not necessarily the optimum option as published in the literature.Tests show that 90° ribs produce a higher heat transfer for the relative roughness height of 0.092.