Influence of rib height on the local heat transfer distribution and pressure drop in a square channel with 90° continuous and 60° V-broken ribs

Internal channel cooling is employed in advanced gas turbines blade to allow high inlet temperatures so as to achieve high thrust/weight ratios and low specific fuel consumption. The objective of the present work is to study the effect of rib height to the hydraulic diameter ratio on the local heat transfer distributions in a double wall ribbed square channel with 90 degrees continuous attached and 60 degrees V-broken ribs. The effect of detachment of the rib in case of broken ribs on the heat transfer characteristics is also presented. Reynolds number based on duct hydraulic diameter is ranging from 10,000 to 30,000. A thin stainless steel foil of 0.05 mm thickness is used as heater and infrared thermography technique is used to obtain the local temperature distribution on the surface. The images are captured in the periodically fully developed region of the channel. It is observed that the heat transfer augmentations in the channel with 90 degrees continuous attached ribs increase with increase in the rib height to hydraulic diameter ratio (e/D) but only at the cost of the pressure drop across the test section. The enhancements caused by 60 degrees V-broken ribs are higher than those of 90 degrees continuous attached ribs and also result in lower pressure drops. But, with an increase in the rib height, the enhancements are found to decrease in channel with broken ribs. The effect of detachment incase of broken ribs is not distinctly observed. The heat transfer characteristics degraded with increase in the rib height in both attached and detached broken ribbed cases. (C) 2008 Elsevier Ltd. All rights reserved.