Experimental investigation on heat transfer and friction characteristics of ribbed rectangular channels using steam as coolant

Heat transfer and friction characteristics of steam flow in ten different rectangular channels with ribs on two opposite walls have been investigated experimentally in this article. To simulate the actual geometry and heat transfer structure of gas turbine blade/vane internal cooling passage, each of the test channels was made by welding four stainless steel plates. The aspect ratio of these steam-cooled channels was 1/4, 1/2, 1, 2 and 4. The rib angle-of-attack was 30°, 45°, 60° and 90°. The Reynolds number range was 10,000-80,000. The pitch-to-rib height ratio (p/e) was kept at 10. The rib height to hydraulic diameter ratios (e/D) were 0.078 for W/H=0.25 and 0.047 for W/H=2, 1 and 0.5. The results show that the highest heat transfer accompanied by the highest friction factor occurred at the rib angle α=60°. The effect of rib angle on the f/f₀ and the Nu/Nu₀ values is reduced gradually with the channel aspect ratio ranging from 4 to 1/4. When the aspect ratio varies from 0.25 to 4, the Nu values increase 35% and the f/f₀ values increase 4.7 times. Semi-empirical correlations of heat transfer and friction are developed to account for channel aspect ratio, rib angle and Reynolds number.