Local heat transfer distribution in a square channel with 90° continuous, 90° saw tooth profiled and 60° 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 study is to measure the local heat transfer distributions in a double wall ribbed square channel with 90° continuous, 90° saw tooth profiled and 60° V-broken ribs. Comparison is made between the 90° continuous ribs (P/e = 7 and 10 for a e/D = 0.15) and 90° saw tooth profiled rib configurations (P/e = 7 for an e/D = 0.15) for the same rib height to the hydraulic diameter ratio (e/D). The effect of pitch to rib height ratio (P/e = 7.5,10 and 12) of 60° V-broken ribbed channel with a constant rib height to hydraulic diameter ratio (e/D) of 0.0625 on the local heat transfer distribution is studied. The 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° saw tooth profiled ribs are comparable with those of 90° continuous ribs. The enhancements caused by 60° V-broken ribs are higher than those of 90° continuous ribs. The effect of pitch to the rib height ratio (P/e) is not significant for channel with 60° V-broken ribs for a given rib height to hydraulic diameter ratio (e/D = 0.0625).